# title: Create a Message url: https://platform.claude.com/docs/en/api/beta/messages/create

# Create a Message

POST /v1/messages

Send a structured list of input messages with text and/or image content, and the model will generate the next message in the conversation.

The Messages API can be used for either single queries or stateless multi-turn conversations.

Learn more about the Messages API in our user guide

# Headers

• "anthropic-beta": optional array of AnthropicBeta

  Optional header to specify the beta version(s) you want to use.

  • string

  • "message-batches-2024-09-24" or "prompt-caching-2024-07-31" or "computer-use-2024-10-22" or 43 more

    • "message-batches-2024-09-24"

    • "prompt-caching-2024-07-31"

    • "computer-use-2024-10-22"

    • "computer-use-2025-01-24"

    • "pdfs-2024-09-25"

    • "token-counting-2024-11-01"

    • "token-efficient-tools-2025-02-19"

    • "output-128k-2025-02-19"

    • "files-api-2025-04-14"

    • "mcp-client-2025-04-04"

    • "mcp-client-2025-11-20"

    • "dev-full-thinking-2025-05-14"

    • "interleaved-thinking-2025-05-14"

    • "code-execution-2025-05-22"

    • "extended-cache-ttl-2025-04-11"

    • "context-1m-2025-08-07"

    • "context-management-2025-06-27"

    • "model-context-window-exceeded-2025-08-26"

    • "skills-2025-10-02"

    • "fast-mode-2026-02-01"

    • "output-300k-2026-03-24"

    • "user-profiles-2026-03-24"

    • "user-profiles-2026-08-18"

    • "user-profiles-2026-09-04"

    • "advisor-tool-2026-03-01"

    • "managed-agents-2026-04-01"

    • "cache-diagnosis-2026-04-07"

    • "dreaming-2026-04-21"

    • "thinking-token-count-2026-05-13"

    • "server-side-fallback-2026-06-01"

    • "server-side-fallback-2026-07-01"

    • "fallback-credit-2026-06-01"

    • "fallback-credit-2026-07-01"

    • "agent-memory-2026-07-22"

    • "mid-conversation-tool-changes-2026-07-01"

    • "compact-2026-01-12"

    • "computer-use-2025-11-24"

    • "mcp-tunnels-2026-06-22"

    • "structured-outputs-2025-11-13"

    • "task-budgets-2026-03-13"

    • "thinking-display-updates-2026-08-18"

    • "ce-user-management-2026-07-13"

    • "mid-conversation-output-config-2026-07-01"

    • "thinking-binding-controls-2026-08-01"

    • "mid-conversation-system-clear-at-2026-08-21"

    • "compact-2026-09-04"

• "anthropic-user-profile-id": optional string

  The user profile ID to attribute this request to. Use when acting on behalf of a party other than your organization. Requires the user-profiles beta header.

• "anthropic-workspace-id": optional string

# Body parameters

• max_tokens: number

  The maximum number of tokens to generate before stopping.

  Note that our models may stop before reaching this maximum. This parameter only specifies the absolute maximum number of tokens to generate.

  Set to 0 to populate the prompt cache without generating a response.

  Different models have different maximum values for this parameter. See models for details.

  minimum: 0

• messages: array of BetaMessageParam

  Input messages.

  Our models are trained to operate on alternating user and assistant conversational turns. When creating a new Message, you specify the prior conversational turns with the messages parameter, and the model then generates the next Message in the conversation. Consecutive user or assistant turns in your request will be combined into a single turn.

  Each input message must be an object with a role and content. You can specify a single user-role message, or you can include multiple user and assistant messages.

  If the final message uses the assistant role, the response content will continue immediately from the content in that message. This can be used to constrain part of the model's response.

  Example with a single user message:

  jsonCopy

  [{"role": "user", "content": "Hello, Claude"}]

  Example with multiple conversational turns:

  jsonCopy

  [
    {"role": "user", "content": "Hello there."},
    {"role": "assistant", "content": "Hi, I'm Claude. How can I help you?"},
    {"role": "user", "content": "Can you explain LLMs in plain English?"},
  ]

  Example with a partially-filled response from Claude:

  jsonCopy

  [
    {"role": "user", "content": "What's the Greek name for Sun? (A) Sol (B) Helios (C) Sun"},
    {"role": "assistant", "content": "The best answer is ("},
  ]

  Each input message content may be either a single string or an array of content blocks, where each block has a specific type. Using a string for content is shorthand for an array of one content block of type "text". The following input messages are equivalent:

  jsonCopy

  {"role": "user", "content": "Hello, Claude"}

  jsonCopy

  {"role": "user", "content": [{"type": "text", "text": "Hello, Claude"}]}

  See input examples.

  Note that if you want to include a system prompt, you can use the top-level system parameter — there is no "system" role for input messages in the Messages API.

  There is a limit of 100,000 messages in a single request.

  • content: string or array of BetaContentBlockParam

    • string

    • array of BetaContentBlockParam

      • BetaTextBlockParam object

        • type: "text"

        • text: string

          minLength: 1

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

          • type: "ephemeral"

          • ttl: optional "5m" or "1h"

            The time-to-live for the cache control breakpoint.

            This may be one the following values:

            • 5m: 5 minutes
            • 1h: 1 hour

            Defaults to 5m. See prompt caching pricing for details.

            • "5m"

            • "1h"

        • citations: optional array of BetaTextCitationParam or null

          • BetaCitationCharLocationParam object

            • type: "char_location"

            • cited_text: string

            • document_index: number

              minimum: 0

            • document_title: string or null

              maxLength: 500, minLength: 1

            • end_char_index: number

            • start_char_index: number

              minimum: 0

          • BetaCitationPageLocationParam object

            • type: "page_location"

            • cited_text: string

            • document_index: number

              minimum: 0

            • document_title: string or null

              maxLength: 500, minLength: 1

            • end_page_number: number

            • start_page_number: number

              minimum: 1

          • BetaCitationContentBlockLocationParam object

            • type: "content_block_location"

            • cited_text: string

              The full text of the cited block range, concatenated.

              Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

            • document_index: number

              minimum: 0

            • document_title: string or null

              maxLength: 500, minLength: 1

            • end_block_index: number

              Exclusive 0-based end index of the cited block range in the source's content array.

              Always greater than start_block_index; a single-block citation has end_block_index = start_block_index + 1.

            • start_block_index: number

              0-based index of the first cited block in the source's content array.

              minimum: 0

          • BetaCitationWebSearchResultLocationParam object

            • type: "web_search_result_location"

            • cited_text: string

            • encrypted_index: string

            • title: string or null

              maxLength: 512, minLength: 1

            • url: string

              minLength: 1

          • BetaCitationSearchResultLocationParam object

            • type: "search_result_location"

            • cited_text: string

              The full text of the cited block range, concatenated.

              Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

            • end_block_index: number

              Exclusive 0-based end index of the cited block range in the source's content array.

              Always greater than start_block_index; a single-block citation has end_block_index = start_block_index + 1.

            • search_result_index: number

              0-based index of the cited search result among all search_result content blocks in the request, in the order they appear across messages and tool results.

              Counted separately from document_index; server-side web search results are not included in this count.

              minimum: 0

            • source: string

            • start_block_index: number

              0-based index of the first cited block in the source's content array.

              minimum: 0

            • title: string or null

      • BetaImageBlockParam object

        • type: "image"

        • source: BetaBase64ImageSource or BetaURLImageSource or BetaFileImageSource

          • BetaBase64ImageSource object

            • type: "base64"

            • data: string

              format: byte

            • media_type: "image/jpeg" or "image/png" or "image/gif" or "image/webp"

              • "image/jpeg"

              • "image/png"

              • "image/gif"

              • "image/webp"

          • BetaURLImageSource object

            • type: "url"

            • url: string

          • BetaFileImageSource object

            • type: "file"

            • file_id: string

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • transformations: optional BetaImageTransformationsParam or null

          Configures the transformations the server applies to this image before the model observes it. Each key names a condition the server transforms images for; its value selects the transformation applied. Omitted keys keep their default behavior, and an empty object is equivalent to omitting the field.

          • oversized_image: optional "downsize" or "error"

            What the server does when this image exceeds the model's maximum image size. "downsize" (the default) scales the image down to fit, which changes the dimensions the model observes without telling you. "error" instead rejects the request with a 400 error naming the image's dimensions and the largest dimensions that fit, so you can scale the image deliberately — your image is never silently scaled down.

            • "downsize"

            • "error"

      • BetaRequestDocumentBlock object

        • type: "document"

        • source: BetaBase64PDFSource or BetaPlainTextSource or BetaContentBlockSource or 2 more

          • BetaBase64PDFSource object

            • type: "base64"

            • data: string

              format: byte

            • media_type: "application/pdf"

          • BetaPlainTextSource object

            • type: "text"

            • data: string

            • media_type: "text/plain"

          • BetaContentBlockSource object

            • type: "content"

            • content: string or array of BetaContentBlockSourceContent

              • string

              • BetaContentBlockSourceContent = array of BetaContentBlockSourceContent

                • BetaTextBlockParam object

                • BetaImageBlockParam object

          • BetaURLPDFSource object

            • type: "url"

            • url: string

          • BetaFileDocumentSource object

            • type: "file"

            • file_id: string

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • citations: optional BetaCitationsConfigParam or null

          • enabled: optional boolean

        • context: optional string or null

          minLength: 1

        • title: optional string or null

          maxLength: 500, minLength: 1

      • BetaSearchResultBlockParam object

        • type: "search_result"

        • content: array of BetaTextBlockParam

          • type: "text"

          • text: string

            minLength: 1

          • cache_control: optional BetaCacheControlEphemeral or null

            Create a cache control breakpoint at this content block.

          • citations: optional array of BetaTextCitationParam or null

        • source: string

        • title: string

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • citations: optional BetaCitationsConfigParam

      • BetaThinkingBlockParam object

        • type: "thinking"

        • signature: string

          The signature value of this thinking block, exactly as returned by the API in a previous response. Used to verify that the block was generated by Claude.

          Thinking blocks must be passed back unmodified and in their original order; a modified block results in a 400 invalid_request_error.

        • thinking: string

          The thinking text of this block as returned by the API.

      • BetaRedactedThinkingBlockParam object

        • type: "redacted_thinking"

        • data: string

          The data value of this redacted thinking block, exactly as returned by the API in a previous response. Opaque and encrypted; pass it back unchanged.

      • BetaToolUseBlockParam object

        • type: "tool_use"

        • id: string

          pattern: ^[1]+$

        • input: map[unknown]

        • name: string

          maxLength: 200, minLength: 1

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          • BetaDirectCaller object

            Tool invocation directly from the model.

            • type: "direct"

          • BetaServerToolCaller object

            Tool invocation generated by a server-side tool.

            • type: "code_execution_20250825"

            • tool_id: string

              pattern: ^srvtoolu_[a-zA-Z0-9_]+$

          • BetaServerToolCaller20260120 object

            • type: "code_execution_20260120"

            • tool_id: string

              pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • toolset_name: optional string or null

          For a toolset member tool_use, the toolset family this member belongs to.

          maxLength: 64, minLength: 1, pattern: ^[2]+$

      • BetaToolResultBlockParam object

        • type: "tool_result"

        • tool_use_id: string

          pattern: ^[3]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • content: optional string or array of BetaTextBlockParam or BetaImageBlockParam or BetaSearchResultBlockParam or 3 more

          • string

          • array of BetaTextBlockParam or BetaImageBlockParam or BetaSearchResultBlockParam or 3 more

            • BetaTextBlockParam object

            • BetaImageBlockParam object

            • BetaSearchResultBlockParam object

            • BetaRequestDocumentBlock object

            • BetaToolReferenceBlockParam object

              Tool reference block that can be included in tool_result content.

              • type: "tool_reference"

              • tool_name: string

                maxLength: 256, minLength: 1, pattern: ^[4]{1,256}$

              • cache_control: optional BetaCacheControlEphemeral or null

                Create a cache control breakpoint at this content block.

            • BetaBrowserStateBlockParam object

              The caller's browser state after a browser toolset member call — the full inventory of open tabs, which tab is active, and any side effects (tabs opened, download state changes) the call produced.

              At most one per tool_result, only on a non-error result answering a browser toolset member tool_use. The server renders the model-visible text from it; the model never sees the raw fields.

              • type: "browser_state"

              • tabs: array of BetaBrowserStateTabEntry

                All tabs open in the browser after this call — the full inventory, not a delta. May be empty. Whenever non-empty, exactly one entry carries active: true.

                maxItems: 100

                • tab_id: string

                  The caller-assigned identifier for this tab, unique within the inventory.

                  maxLength: 4096, minLength: 1, pattern: ^[5]*$

                • title: string

                  The title of the page the tab is showing. May be empty.

                  maxLength: 4096, pattern: ^[6]*$

                • url: string

                  The URL of the page the tab is showing. May be empty.

                  maxLength: 4096, pattern: ^[7]*$

                • active: optional boolean

                  Whether this tab is the active tab after this call. Whenever tabs is non-empty, exactly one entry is marked active: true.

              • cache_control: optional BetaCacheControlEphemeral or null

                Create a cache control breakpoint at this content block.

              • state_changes: optional array of BetaBrowserStateChange or null

                Tabs opened and download state changes during this call. "Nothing to report" is expressed by omitting the field, never by an empty list.

                maxItems: 200, minItems: 1

                • BetaBrowserStateChangeTabOpened object

                  A tab this call's execution opened that remains open at its end — the creation delta of the tabs inventory, not an event log.

                  Carries only the tab_id; the tab's title and url live on its tabs entry, which must include the same tab_id. A tab opened during a failed call gets no deferred tab_opened; it simply appears in the next result's tabs inventory.

                  • type: "tab_opened"

                  • tab_id: string

                    The tab_id of the opened tab, present in tabs.

                    maxLength: 4096, minLength: 1, pattern: ^[8]*$

                • BetaBrowserStateChangeDownloadStarted object

                  A file download that started during this call.

                  • type: "download_started"

                  • download_id: string

                    The caller-assigned identifier for this download, stable across the state changes reporting it.

                    maxLength: 4096, minLength: 1, pattern: ^[9]*$

                  • url: string

                    The final post-redirect URL the download was served from.

                    maxLength: 4096, pattern: ^[10]*$

                • BetaBrowserStateChangeDownloadCompleted object

                  A file download that finished during this call, reported with the same download_id as its download_started — or without a prior download_started, when the download finished during the call that started it (at most one state change per download_id per result).

                  • type: "download_completed"

                  • download_id: string

                    The caller-assigned identifier for this download, stable across the state changes reporting it.

                    maxLength: 4096, minLength: 1, pattern: ^[11]*$

                  • url: string

                    The final post-redirect URL the download was served from.

                    maxLength: 4096, pattern: ^[12]*$

                  • path: optional string or null

                    Where the executor saved the file, on the executor's filesystem. Only included when another tool in the same environment can read the file at that path.

                    pattern: ^[13]*$, maxLength: 4096

                  • size_bytes: optional number or null

                    The completed download's size.

                    minimum: 0

                • BetaBrowserStateChangeDownloadFailed object

                  A file download that failed — or was cancelled — during this call.

                  • type: "download_failed"

                  • download_id: string

                    The caller-assigned identifier for this download, stable across the state changes reporting it.

                    maxLength: 4096, minLength: 1, pattern: ^[14]*$

                  • url: string

                    The final post-redirect URL the download was served from.

                    maxLength: 4096, pattern: ^[15]*$

                  • error: optional string or null

                    The failure or cancellation detail, when known.

                    pattern: ^[16]*$, maxLength: 4096

        • is_error: optional boolean

        • toolset_name: optional string or null

          For a toolset member tool_result, the toolset family of the paired tool_use.

          maxLength: 64, minLength: 1, pattern: ^[17]+$

      • BetaServerToolUseBlockParam object

        • type: "server_tool_use"

        • id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • input: map[unknown]

        • name: "advisor" or "web_search" or "web_fetch" or 5 more

          • "advisor"

          • "web_search"

          • "web_fetch"

          • "code_execution"

          • "bash_code_execution"

          • "text_editor_code_execution"

          • "tool_search_tool_regex"

          • "tool_search_tool_bm25"

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          • BetaDirectCaller object

            Tool invocation directly from the model.

          • BetaServerToolCaller object

            Tool invocation generated by a server-side tool.

          • BetaServerToolCaller20260120 object

      • BetaWebSearchToolResultBlockParam object

        • type: "web_search_tool_result"

        • content: BetaWebSearchToolResultBlockParamContent

          • ResultBlock = array of BetaWebSearchResultBlockParam

            • type: "web_search_result"

            • encrypted_content: string

            • title: string

            • url: string

            • page_age: optional string or null

          • BetaWebSearchToolRequestError object

            • type: "web_search_tool_result_error"

            • error_code: BetaWebSearchToolResultErrorCode

              • "invalid_tool_input"

              • "unavailable"

              • "max_uses_exceeded"

              • "too_many_requests"

              • "query_too_long"

              • "request_too_large"

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          • BetaDirectCaller object

            Tool invocation directly from the model.

          • BetaServerToolCaller object

            Tool invocation generated by a server-side tool.

          • BetaServerToolCaller20260120 object

      • BetaWebFetchToolResultBlockParam object

        • type: "web_fetch_tool_result"

        • content: BetaWebFetchToolResultErrorBlockParam or BetaWebFetchBlockParam

          • BetaWebFetchToolResultErrorBlockParam object

            • type: "web_fetch_tool_result_error"

            • error_code: BetaWebFetchToolResultErrorCode

              • "invalid_tool_input"

              • "url_too_long"

              • "url_not_allowed"

              • "url_not_in_prior_context"

              • "url_not_accessible"

              • "unsupported_content_type"

              • "too_many_requests"

              • "max_uses_exceeded"

              • "unavailable"

              • "content_too_large"

          • BetaWebFetchBlockParam object

            • type: "web_fetch_result"

            • content: BetaRequestDocumentBlock

            • url: string

              Fetched content URL

            • retrieved_at: optional string or null

              ISO 8601 timestamp when the content was retrieved

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

          • BetaDirectCaller object

            Tool invocation directly from the model.

          • BetaServerToolCaller object

            Tool invocation generated by a server-side tool.

          • BetaServerToolCaller20260120 object

      • BetaAdvisorToolResultBlockParam object

        • type: "advisor_tool_result"

        • content: BetaAdvisorToolResultErrorParam or BetaAdvisorResultBlockParam or BetaAdvisorRedactedResultBlockParam

          • BetaAdvisorToolResultErrorParam object

            • type: "advisor_tool_result_error"

            • error_code: "max_uses_exceeded" or "prompt_too_long" or "too_many_requests" or 4 more

              • "max_uses_exceeded"

              • "prompt_too_long"

              • "too_many_requests"

              • "overloaded"

              • "unavailable"

              • "execution_time_exceeded"

              • "model_not_found"

          • BetaAdvisorResultBlockParam object

            • type: "advisor_result"

            • text: string

            • stop_reason: optional string or null

          • BetaAdvisorRedactedResultBlockParam object

            • type: "advisor_redacted_result"

            • encrypted_content: string

              Opaque blob produced by a prior response; must be round-tripped verbatim.

            • stop_reason: optional string or null

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaCodeExecutionToolResultBlockParam object

        • type: "code_execution_tool_result"

        • content: BetaCodeExecutionToolResultBlockParamContent

          • BetaCodeExecutionToolResultErrorParam object

            • type: "code_execution_tool_result_error"

            • error_code: BetaCodeExecutionToolResultErrorCode

              • "invalid_tool_input"

              • "unavailable"

              • "too_many_requests"

              • "execution_time_exceeded"

          • BetaCodeExecutionResultBlockParam object

            • type: "code_execution_result"

            • content: array of BetaCodeExecutionOutputBlockParam

              • type: "code_execution_output"

              • file_id: string

            • return_code: number

            • stderr: string

            • stdout: string

          • BetaEncryptedCodeExecutionResultBlockParam object

            Code execution result with encrypted stdout for PFC + web_search results.

            • type: "encrypted_code_execution_result"

            • content: array of BetaCodeExecutionOutputBlockParam

              • type: "code_execution_output"

              • file_id: string

            • encrypted_stdout: string

            • return_code: number

            • stderr: string

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaBashCodeExecutionToolResultBlockParam object

        • type: "bash_code_execution_tool_result"

        • content: BetaBashCodeExecutionToolResultErrorParam or BetaBashCodeExecutionResultBlockParam

          • BetaBashCodeExecutionToolResultErrorParam object

            • type: "bash_code_execution_tool_result_error"

            • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or 2 more

              • "invalid_tool_input"

              • "unavailable"

              • "too_many_requests"

              • "execution_time_exceeded"

              • "output_file_too_large"

          • BetaBashCodeExecutionResultBlockParam object

            • type: "bash_code_execution_result"

            • content: array of BetaBashCodeExecutionOutputBlockParam

              • type: "bash_code_execution_output"

              • file_id: string

            • return_code: number

            • stderr: string

            • stdout: string

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaTextEditorCodeExecutionToolResultBlockParam object

        • type: "text_editor_code_execution_tool_result"

        • content: BetaTextEditorCodeExecutionToolResultErrorParam or BetaTextEditorCodeExecutionViewResultBlockParam or BetaTextEditorCodeExecutionCreateResultBlockParam or BetaTextEditorCodeExecutionStrReplaceResultBlockParam

          • BetaTextEditorCodeExecutionToolResultErrorParam object

            • type: "text_editor_code_execution_tool_result_error"

            • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or 2 more

              • "invalid_tool_input"

              • "unavailable"

              • "too_many_requests"

              • "execution_time_exceeded"

              • "file_not_found"

            • error_message: optional string or null

          • BetaTextEditorCodeExecutionViewResultBlockParam object

            • type: "text_editor_code_execution_view_result"

            • content: string

            • file_type: "text" or "image" or "pdf"

              • "text"

              • "image"

              • "pdf"

            • num_lines: optional number or null

            • start_line: optional number or null

            • total_lines: optional number or null

          • BetaTextEditorCodeExecutionCreateResultBlockParam object

            • type: "text_editor_code_execution_create_result"

            • is_file_update: boolean

          • BetaTextEditorCodeExecutionStrReplaceResultBlockParam object

            • type: "text_editor_code_execution_str_replace_result"

            • lines: optional array of string or null

            • new_lines: optional number or null

            • new_start: optional number or null

            • old_lines: optional number or null

            • old_start: optional number or null

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaToolSearchToolResultBlockParam object

        • type: "tool_search_tool_result"

        • content: BetaToolSearchToolResultErrorParam or BetaToolSearchToolSearchResultBlockParam

          • BetaToolSearchToolResultErrorParam object

            • type: "tool_search_tool_result_error"

            • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or "execution_time_exceeded"

              • "invalid_tool_input"

              • "unavailable"

              • "too_many_requests"

              • "execution_time_exceeded"

            • error_message: optional string or null

          • BetaToolSearchToolSearchResultBlockParam object

            • type: "tool_search_tool_search_result"

            • tool_references: array of BetaToolReferenceBlockParam

              • type: "tool_reference"

              • tool_name: string

                maxLength: 256, minLength: 1, pattern: ^[18]{1,256}$

              • cache_control: optional BetaCacheControlEphemeral or null

                Create a cache control breakpoint at this content block.

        • tool_use_id: string

          pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaMCPToolUseBlockParam object

        • type: "mcp_tool_use"

        • id: string

          pattern: ^[19]+$

        • input: map[unknown]

        • name: string

        • server_name: string

          The name of the MCP server

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaRequestMCPToolResultBlockParam object

        • type: "mcp_tool_result"

        • tool_use_id: string

          pattern: ^[20]+$

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • content: optional string or array of BetaTextBlockParam

          • string

          • BetaMCPToolResultBlockParamContent = array of BetaTextBlockParam

            • type: "text"

            • text: string

              minLength: 1

            • cache_control: optional BetaCacheControlEphemeral or null

              Create a cache control breakpoint at this content block.

            • citations: optional array of BetaTextCitationParam or null

        • is_error: optional boolean

      • BetaContainerUploadBlockParam object

        A content block that represents a file to be uploaded to the container Files uploaded via this block will be available in the container's input directory.

        • type: "container_upload"

        • file_id: string

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaCompactionBlockParam object

        A compaction block containing summary of previous context.

        Users should round-trip these blocks from responses to subsequent requests to maintain context across compaction boundaries.

        When content is None, the block represents a failed compaction. The server treats these as no-ops. Empty string content is not allowed.

        • type: "compaction"

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

        • content: optional string or null

          Summary of previously compacted content, or null if compaction failed

        • encrypted_content: optional string or null

          Opaque metadata from prior compaction, to be round-tripped verbatim

        • signature: optional string or null

          The block's signature as returned, to be sent back verbatim

      • BetaRequestToolAdditionBlock object

        Mid-conversation directive to surface a declared tool.

        tool references a tool (or MCP toolset) by name from the request's tools; it is offered to the model from this point in the conversation onward.

        • type: "tool_addition"

        • tool: BetaToolChangeToolReference or BetaToolChangeMCPToolReference or BetaToolChangeMCPToolsetReference

          • BetaToolChangeToolReference object

            Reference to a single tool the caller declared directly in tools[]. Does not accept the composed {server}_{name} form the server assigns to MCP-resolved tools — use mcp_tool_reference or mcp_toolset_reference for those.

            • type: "tool_reference"

            • name: string

              pattern: ^[21]{1,128}$

          • BetaToolChangeMCPToolReference object

            Reference to a single MCP tool by its server and remote name; the same server_name/name pair mcp_tool_use carries.

            • type: "mcp_tool_reference"

            • name: string

            • server_name: string

          • BetaToolChangeMCPToolsetReference object

            Reference to every tool in the named MCP server's toolset.

            • type: "mcp_toolset_reference"

            • server_name: string

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaRequestToolRemovalBlock object

        Mid-conversation directive to withdraw a tool.

        tool references a tool (or MCP toolset) by name from the request's tools; it is no longer offered to the model from this point in the conversation onward.

        • type: "tool_removal"

        • tool: BetaToolChangeToolReference or BetaToolChangeMCPToolReference or BetaToolChangeMCPToolsetReference

          • BetaToolChangeToolReference object

            Reference to a single tool the caller declared directly in tools[]. Does not accept the composed {server}_{name} form the server assigns to MCP-resolved tools — use mcp_tool_reference or mcp_toolset_reference for those.

          • BetaToolChangeMCPToolReference object

            Reference to a single MCP tool by its server and remote name; the same server_name/name pair mcp_tool_use carries.

          • BetaToolChangeMCPToolsetReference object

            Reference to every tool in the named MCP server's toolset.

        • cache_control: optional BetaCacheControlEphemeral or null

          Create a cache control breakpoint at this content block.

      • BetaFallbackBlockParam object

        A fallback block echoed back from a prior response.

        Accepted in messages[].content and not rendered into the prompt; not validated against the request's fallbacks chain or top-level model.

        Echo the assistant turn back verbatim, including this block in its original position. The block marks the boundary between content produced before and after a fallback hop, and the server relies on that boundary to validate the turn: when thinking runs flank the boundary, omitting the block merges them into one span the server cannot validate (the request is rejected), and moving it into the middle of a single run is likewise rejected; between non-thinking blocks the block's placement has no validation effect.

        • type: "fallback"

        • from: BetaFallbackInfoParam

          Identifies one hop of a fallback transition.

          • model: Model

            The model that will complete your prompt.

            See models for additional details and options.

            • "claude-fable-5-1" or "claude-mythos-5-1" or "claude-sonnet-5" or 14 more

              The model that will complete your prompt.

              See models for additional details and options.

              • "claude-fable-5-1"

                Frontier intelligence for ambitious tasks across coding, scientific discovery, and enterprise workflows

              • "claude-mythos-5-1"

                Our most capable model for cybersecurity and biology research, available through trusted access programs

              • "claude-sonnet-5"

                High-performance model for coding and agents

              • "claude-fable-5"

                Next generation of intelligence for the hardest knowledge work and coding problems

              • "claude-mythos-5"

                Most capable model for cybersecurity and biology research

              • "claude-opus-5"

                Powerful intelligence for long-running agents and coding

              • "claude-opus-4-8"

                Powerful intelligence for long-running agents and coding

              • "claude-opus-4-7"

                Powerful intelligence for long-running agents and coding

              • "claude-mythos-preview"

                New class of intelligence, strongest in coding and cybersecurity

              • "claude-opus-4-6"

                Powerful intelligence for long-running agents and coding

              • "claude-sonnet-4-6"

                Best combination of speed and intelligence

              • "claude-haiku-4-5"

                Fastest model with near-frontier intelligence

              • "claude-haiku-4-5-20251001"

                Fastest model with near-frontier intelligence

              • "claude-opus-4-5"

                Powerful intelligence for long-running agents and coding

              • "claude-opus-4-5-20251101"

                Powerful intelligence for long-running agents and coding

              • "claude-sonnet-4-5"

                High-performance model for agents and coding

              • "claude-sonnet-4-5-20250929"

                High-performance model for agents and coding

            • string

        • to: BetaFallbackInfoParam

          Identifies one hop of a fallback transition.

        • trigger: optional unknown

          The response block's trigger, echoed verbatim. Accepted and ignored by the server; any object or null is allowed.

  • role: "user" or "assistant" or "system"

    • "user"

    • "assistant"

    • "system"

  • clear_at: optional "next_user_message" or "never" or null

    How long this system message's text stays in front of the model. "never" (the default) renders it on every request that includes it. "next_user_message" renders it only for the user turn it follows: once a later role: "user" message exists in messages the message stays in the array (send it unchanged) but is no longer shown to the model. Only permitted on role: "system" messages.

    • "next_user_message"

    • "never"

  • output_config: optional BetaSystemMessageOutputConfig or null

    Per-message output configuration on a role:"system" input message.

    Fields here apply per-turn; format remains top-level only. An empty {} is accepted on a message that carries content; a message with neither content nor output_config fields is rejected.

    • effort: optional "low" or "medium" or "high" or 2 more or null

      All possible effort levels.

      • "low"

      • "medium"

      • "high"

      • "xhigh"

      • "max"

• model: Model

  The model that will complete your prompt.

  See models for additional details and options.

• cache_control: optional BetaCacheControlEphemeral or null

  Top-level cache control automatically applies a cache_control marker to the last cacheable block in the request.

• compaction: optional BetaCompactionConfig or null

  Compact the whole conversation and return a signed compaction block, alone, that a later request sends back first in messages, in place of the messages it summarizes. There is no trigger and no pause flag: sending the parameter compacts, and nothing is sampled after the block.

  The summarization prompt is the server's own unless instructions are given, which then replace it for this request; a value that is empty or only whitespace counts as absent.

  • type: "summarize"

  • instructions: optional string or null

    Replaces the server's default summarization prompt for this request. An empty or whitespace-only value counts as absent.

    maxLength: 16384

• container: optional BetaContainerParams or string or null

  Container identifier for reuse across requests.

  • BetaContainerParams object

    Container parameters with skills to be loaded.

    • id: optional string or null

      Container id

    • skills: optional array of BetaSkillParams or null

      List of skills to load in the container

      maxItems: 20

      • type: "anthropic" or "custom"

        Type of skill - either 'anthropic' (built-in) or 'custom' (user-defined)

        • "anthropic"

        • "custom"

      • skill_id: string

        Skill ID

        maxLength: 64, minLength: 1

      • version: optional string

        Skill version or 'latest' for most recent version

        maxLength: 64, minLength: 1

  • string

• context_management: optional BetaContextManagementConfig or null

  Context management configuration.

  This allows you to control how Claude manages context across multiple requests, such as whether to clear function results or not.

  • edits: optional array of BetaClearToolUses20250919Edit or BetaClearThinking20251015Edit or BetaCompact20260112Edit

    List of context management edits to apply

    minItems: 0

    • BetaClearToolUses20250919Edit object

      • type: "clear_tool_uses_20250919"

      • clear_at_least: optional BetaInputTokensClearAtLeast or null

        Minimum number of tokens that must be cleared when triggered. Context will only be modified if at least this many tokens can be removed.

        • type: "input_tokens"

        • value: number

          minimum: 0

      • clear_tool_inputs: optional boolean or array of string or null

        Whether to clear all tool inputs (bool) or specific tool inputs to clear (list)

        • boolean

        • array of string

      • exclude_tools: optional array of string or null

        Tool names whose uses are preserved from clearing

      • keep: optional BetaToolUsesKeep

        Number of tool uses to retain in the conversation

        • type: "tool_uses"

        • value: number

          minimum: 0

      • trigger: optional BetaInputTokensTrigger or BetaToolUsesTrigger

        Condition that triggers the context management strategy

        • BetaInputTokensTrigger object

          • type: "input_tokens"

          • value: number

            minimum: 1

        • BetaToolUsesTrigger object

          • type: "tool_uses"

          • value: number

            minimum: 1

    • BetaClearThinking20251015Edit object

      • type: "clear_thinking_20251015"

      • keep: optional BetaThinkingTurns or BetaAllThinkingTurns or "all"

        Number of most recent assistant turns to keep thinking blocks for. Older turns will have their thinking blocks removed.

        • BetaThinkingTurns object

          • type: "thinking_turns"

          • value: number

            minimum: 1

        • BetaAllThinkingTurns object

          • type: "all"

        • "all"

    • BetaCompact20260112Edit object

      Automatically compact older context when reaching the configured trigger threshold.

      • type: "compact_20260112"

      • instructions: optional string or null

        Additional instructions for summarization.

      • pause_after_compaction: optional boolean

        Whether to pause after compaction and return the compaction block to the user.

      • trigger: optional BetaInputTokensTrigger or null

        When to trigger compaction. Defaults to 150000 input tokens.

• diagnostics: optional BetaDiagnosticsParam or null

  Request-level diagnostics. Currently carries the previous response id for prompt-cache divergence reporting.

  • previous_message_id: optional string or null

    The id (msg_...) from this client's previous /v1/messages response. The server compares that request's prompt fingerprint against this one and returns diagnostics.cache_miss_reason when the prompt-cache prefix could not be reused. Pass null on the first turn to opt in without a prior message to compare.

    maxLength: 256

• fallback_credit_token: optional string or BetaFallbackCreditTokenParam or null

  The fallback_credit_token from a prior refusal's stop_details.

  When a preceding request was refused and returned a fallback_credit_token, pass that code here on the retry to have the retry's cache-creation tokens for the prefix that was warm on the refused model billed at the cache-read rate. Must be redeemed by the same organization and workspace, with the same request body (optionally extended by one appended assistant message whose content is the partial text — with any trailing whitespace stripped from the final text block — and paired server-tool blocks streamed before the refusal; the appended-assistant form is not available for requests with output_format set or forced tool_choice), on an eligible fallback model, on the same platform, and within 5 minutes of the refusal; a mismatch is a 400. A token minted mid-server-tool-loop whose partial content was continuable may only be redeemed with the appended-assistant form — if an exact-body retry is rejected with a 400 saying the token must be redeemed by continuing the partial response, retry with the appended-assistant form instead.

  When the appended-assistant form is used on a model that otherwise disallows assistant-turn prefill, this token also authorizes that one prefill.

  • string

  • BetaFallbackCreditTokenParam object

    Object form of fallback_credit_token: the token plus a redemption mode.

    Requires anthropic-beta: fallback-credit-2026-07-01; without that header the field accepts the bare string only. The bare string and the mode-less object are equivalent (both select strict), so wrapping an existing token changes nothing by itself.

    • token: string

      The opaque fallback_credit_token from a prior refusal's stop_details — the same string the bare-string form carries.

      maxLength: 2048, minLength: 1

    • mode: optional "strict" or "best_effort"

      How a failing token affects the retry. strict (the default, and the bare-string behavior): a failing redemption is a 400 and the retry is not served. best_effort: the retry is served either way — a token-layer failure no longer rejects the request; the retry proceeds at normal price and the outcome is reported on the response's usage.fallback_credit. Two failures stay hard in both modes: a malformed token, and combining fallback_credit_token with fallbacks.

      • "strict"

      • "best_effort"

• fallbacks: optional BetaFallbacksParam or null

  Opt-in server-side retry on one or more substitute models when the requested model declines for policy reasons. Tried in order: if the first entry also declines, the second is tried, and so on. The string "default" requests the requested model's server-defined default fallback configuration.

  • array of BetaFallbackParam

    • model: Model

      The model that will complete your prompt.

      See models for additional details and options.

    • max_tokens: optional number or null

    • output_config: optional BetaOutputConfig or null

      • effort: optional "low" or "medium" or "high" or 2 more or null

        All possible effort levels.

        • "low"

        • "medium"

        • "high"

        • "xhigh"

        • "max"

      • format: optional BetaJSONOutputFormat or null

        A schema to specify Claude's output format in responses. See structured outputs

        • type: "json_schema"

        • schema: map[unknown]

          The JSON schema of the format

      • task_budget: optional BetaTokenTaskBudget or null

        User-configurable total token budget across contexts.

        • type: "tokens"

          The budget type. Currently only 'tokens' is supported.

        • total: number

          Total token budget across all contexts in the session.

          minimum: 1024

        • remaining: optional number or null

          Remaining tokens in the budget. Use this to track usage across contexts when implementing compaction client-side. Defaults to total if not provided.

          minimum: 0

    • speed: optional "standard" or "fast" or null

      Inference speed mode. fast provides significantly faster output token generation at premium pricing. Not all models support fast; invalid combinations are rejected at create time.

      • "standard"

      • "fast"

    • thinking: optional BetaThinkingConfigEnabled or BetaThinkingConfigDisabled or BetaThinkingConfigAdaptive or null

      • BetaThinkingConfigEnabled object

        • type: "enabled"

        • budget_tokens: number

          Determines how many tokens Claude can use for its internal reasoning process. Larger budgets can enable more thorough analysis for complex problems, improving response quality.

          Must be ≥1024 and less than max_tokens.

          See extended thinking for details.

          minimum: 1024

        • block_binding: optional BetaThinkingBlockBinding or null

          Controls for block binding: what happens when a thinking block this request sends back fails the conversation check. Every field is optional; an empty object means every default.

          • prefix_mismatch_behavior: optional BetaThinkingPrefixMismatchBehavior or null

            What happens when a thinking block in messages fails the conversation check: it was created in a different conversation, or the messages before it have changed since. "error" (the default) fails the request with a 400 error. "drop_block" removes the failing blocks and the request proceeds; the model no longer sees the dropped reasoning.

            • "error"

            • "drop_block"

        • display: optional "summarized" or "omitted" or "updates" or null

          Controls how thinking content appears in the response. When set to summarized, thinking is returned normally. When set to omitted, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to summarized.

          • "summarized"

          • "omitted"

          • "updates"

      • BetaThinkingConfigDisabled object

        • type: "disabled"

      • BetaThinkingConfigAdaptive object

        • type: "adaptive"

        • block_binding: optional BetaThinkingBlockBinding or null

          Controls for block binding: what happens when a thinking block this request sends back fails the conversation check. Every field is optional; an empty object means every default.

        • display: optional "summarized" or "omitted" or "updates" or null

          Controls how thinking content appears in the response. When set to summarized, thinking is returned normally. When set to omitted, thinking content is redacted but a signature is returned for multi-turn continuity. Defaults to summarized.

          • "summarized"

          • "omitted"

          • "updates"

  • Default = "default"

• inference_geo: optional string or null

  Specifies the geographic region for inference processing. If not specified, the workspace's default_inference_geo is used.

• mcp_servers: optional array of BetaRequestMCPServerURLDefinition

  MCP servers to be utilized in this request

  maxItems: 20

  • type: "url"

  • name: string

  • url: string

  • authorization_token: optional string or null

  • tool_configuration: optional BetaRequestMCPServerToolConfiguration or null

    • allowed_tools: optional array of string or null

    • enabled: optional boolean or null

• metadata: optional BetaMetadata

  An object describing metadata about the request.

  • user_id: optional string or null

    An external identifier for the user who is associated with the request.

    This should be a uuid, hash value, or other opaque identifier. Anthropic may use this id to help detect abuse. Do not include any identifying information such as name, email address, or phone number.

    maxLength: 512

• output_config: optional BetaOutputConfig

  Configuration options for the model's output, such as the output format.

• service_tier: optional "auto" or "standard_only"

  Determines whether to use priority capacity (if available) or standard capacity for this request.

  Anthropic offers different levels of service for your API requests. See service-tiers for details.

  • "auto"

  • "standard_only"

• speed: optional "standard" or "fast" or null

  Inference speed mode. fast provides significantly faster output token generation at premium pricing. Not all models support fast; invalid combinations are rejected at create time.

  • "standard"

  • "fast"

• stop_sequences: optional array of string

  Custom text sequences that will cause the model to stop generating.

  Our models will normally stop when they have naturally completed their turn, which will result in a response stop_reason of "end_turn".

  If you want the model to stop generating when it encounters custom strings of text, you can use the stop_sequences parameter. If the model encounters one of the custom sequences, the response stop_reason value will be "stop_sequence" and the response stop_sequence value will contain the matched stop sequence.

• stream: optional boolean

  Whether to incrementally stream the response using server-sent events.

  See streaming for details.

• system: optional string or array of BetaTextBlockParam

  System prompt.

  A system prompt is a way of providing context and instructions to Claude, such as specifying a particular goal or role. See our guide to system prompts.

  • string

  • array of BetaTextBlockParam

    • type: "text"

    • text: string

      minLength: 1

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • citations: optional array of BetaTextCitationParam or null

• thinking: optional BetaThinkingConfigParam

  Configuration for enabling Claude's extended thinking.

  When enabled, responses include thinking content blocks showing Claude's thinking process before the final answer. Requires a minimum budget of 1,024 tokens and counts towards your max_tokens limit.

  See extended thinking for details.

  • BetaThinkingConfigEnabled object

  • BetaThinkingConfigDisabled object

  • BetaThinkingConfigAdaptive object

• tool_choice: optional BetaToolChoice

  How the model should use the provided tools. The model can use a specific tool, any available tool, decide by itself, or not use tools at all.

  • BetaToolChoiceAuto object

    The model will automatically decide whether to use tools.

    • type: "auto"

    • disable_parallel_tool_use: optional boolean

      Whether to disable parallel tool use.

      Defaults to false. If set to true, the model will output at most one tool use.

  • BetaToolChoiceAny object

    The model will use any available tools.

    • type: "any"

    • disable_parallel_tool_use: optional boolean

      Whether to disable parallel tool use.

      Defaults to false. If set to true, the model will output exactly one tool use.

  • BetaToolChoiceTool object

    The model will use the specified tool with tool_choice.name.

    • type: "tool"

    • name: string

      The name of the tool to use.

    • disable_parallel_tool_use: optional boolean

      Whether to disable parallel tool use.

      Defaults to false. If set to true, the model will output exactly one tool use.

  • BetaToolChoiceNone object

    The model will not be allowed to use tools.

    • type: "none"

• tools: optional array of BetaToolUnion

  Definitions of tools that the model may use.

  If you include tools in your API request, the model may return tool_use content blocks that represent the model's use of those tools. You can then run those tools using the tool input generated by the model and then optionally return results back to the model using tool_result content blocks.

  There are two types of tools: client tools and server tools. The behavior described below applies to client tools. For server tools, see their individual documentation as each has its own behavior (e.g., the web search tool).

  Each tool definition includes:

  • name: Name of the tool.
  • description: Optional, but strongly-recommended description of the tool.
  • input_schema: JSON schema for the tool input shape that the model will produce in tool_use output content blocks.

  For example, if you defined tools as:

  jsonCopy

  [
    {
      "name": "get_stock_price",
      "description": "Get the current stock price for a given ticker symbol.",
      "input_schema": {
        "type": "object",
        "properties": {
          "ticker": {
            "type": "string",
            "description": "The stock ticker symbol, e.g. AAPL for Apple Inc."
          }
        },
        "required": ["ticker"]
      }
    }
  ]

  And then asked the model "What's the S&P 500 at today?", the model might produce tool_use content blocks in the response like this:

  jsonCopy

  [
    {
      "type": "tool_use",
      "id": "toolu_01D7FLrfh4GYq7yT1ULFeyMV",
      "name": "get_stock_price",
      "input": { "ticker": "^GSPC" }
    }
  ]

  You might then run your get_stock_price tool with {"ticker": "^GSPC"} as an input, and return the following back to the model in a subsequent user message:

  jsonCopy

  [
    {
      "type": "tool_result",
      "tool_use_id": "toolu_01D7FLrfh4GYq7yT1ULFeyMV",
      "content": "259.75 USD"
    }
  ]

  Tools can be used for workflows that include running client-side tools and functions, or more generally whenever you want the model to produce a particular JSON structure of output.

  See our guide for more details.

  • BetaTool object

    • type: optional "custom" or null

    • input_schema: object

      JSON schema for this tool's input.

      This defines the shape of the input that your tool accepts and that the model will produce.

      • type: "object"

      • properties: optional map[unknown] or null

      • required: optional array of string or null

    • name: string

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

      maxLength: 128, minLength: 1, pattern: ^[22]{1,128}$

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • description: optional string

      Description of what this tool does.

      Tool descriptions should be as detailed as possible. The more information that the model has about what the tool is and how to use it, the better it will perform. You can use natural language descriptions to reinforce important aspects of the tool input JSON schema.

    • eager_input_streaming: optional boolean or null

      Enable eager input streaming for this tool. When true, tool input parameters will be streamed incrementally as they are generated, and types will be inferred on-the-fly rather than buffering the full JSON output. When false, streaming is disabled for this tool even if the fine-grained-tool-streaming beta is active. When null (default), uses the default behavior based on beta headers.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolBash20241022 object

    • type: "bash_20241022"

    • name: "bash"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolBash20250124 object

    • type: "bash_20250124"

    • name: "bash"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaCodeExecutionTool20250522 object

    • type: "code_execution_20250522"

    • name: "code_execution"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaCodeExecutionTool20250825 object

    • type: "code_execution_20250825"

    • name: "code_execution"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaCodeExecutionTool20260120 object

    Code execution tool with REPL state persistence (daemon mode + gVisor checkpoint).

    • type: "code_execution_20260120"

    • name: "code_execution"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaCodeExecutionTool20260521 object

    Code execution tool with REPL state persistence.

    • type: "code_execution_20260521"

    • name: "code_execution"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaBrowserToolset20260801 object

    The browser toolset: a single tools[] entry (carrying no name) that declares the browser tool family. The model is served the family's tool with any members disabled via configs removed from its schema.

    • type: "browser_toolset_20260801"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • configs: optional BetaBrowserToolsetConfigs or null

      Per-member configuration for browser_toolset_20260801: one optional field per member tool, keyed by the member name — the same name the member's tool_use blocks carry. Every member is an accepted key, and a member's defaults apply wherever its key is absent. Unknown keys are rejected: the field set is this toolset version's complete member set.

      • type: optional BetaBrowserTypeConfig or null

        type's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • close_tab: optional BetaBrowserCloseTabConfig or null

        close_tab's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • double_click: optional BetaBrowserDoubleClickConfig or null

        double_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • file_upload: optional BetaBrowserFileUploadConfig or null

        file_upload's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • find: optional BetaBrowserFindConfig or null

        find's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • form_input: optional BetaBrowserFormInputConfig or null

        form_input's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • get_page_text: optional BetaBrowserGetPageTextConfig or null

        get_page_text's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • hold_key: optional BetaBrowserHoldKeyConfig or null

        hold_key's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • hover: optional BetaBrowserHoverConfig or null

        hover's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • javascript_exec: optional BetaBrowserJavascriptExecConfig or null

        javascript_exec's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • key: optional BetaBrowserKeyConfig or null

        key's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_click: optional BetaBrowserLeftClickConfig or null

        left_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_click_drag: optional BetaBrowserLeftClickDragConfig or null

        left_click_drag's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_mouse_down: optional BetaBrowserLeftMouseDownConfig or null

        left_mouse_down's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_mouse_up: optional BetaBrowserLeftMouseUpConfig or null

        left_mouse_up's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • list_tabs: optional BetaBrowserListTabsConfig or null

        list_tabs's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • middle_click: optional BetaBrowserMiddleClickConfig or null

        middle_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • mouse_move: optional BetaBrowserMouseMoveConfig or null

        mouse_move's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • navigate: optional BetaBrowserNavigateConfig or null

        navigate's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • new_tab: optional BetaBrowserNewTabConfig or null

        new_tab's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • read_console: optional BetaBrowserReadConsoleConfig or null

        read_console's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • read_network: optional BetaBrowserReadNetworkConfig or null

        read_network's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • read_page: optional BetaBrowserReadPageConfig or null

        read_page's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • right_click: optional BetaBrowserRightClickConfig or null

        right_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • screenshot: optional BetaBrowserScreenshotConfig or null

        screenshot's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • scroll: optional BetaBrowserScrollConfig or null

        scroll's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • scroll_to: optional BetaBrowserScrollToConfig or null

        scroll_to's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • switch_tab: optional BetaBrowserSwitchTabConfig or null

        switch_tab's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • triple_click: optional BetaBrowserTripleClickConfig or null

        triple_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • wait: optional BetaBrowserWaitConfig or null

        wait's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • zoom: optional BetaBrowserZoomConfig or null

        zoom's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

  • BetaToolComputerUse20241022 object

    • type: "computer_20241022"

    • display_height_px: number

      The height of the display in pixels.

      minimum: 1

    • display_width_px: number

      The width of the display in pixels.

      minimum: 1

    • name: "computer"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • display_number: optional number or null

      The X11 display number (e.g. 0, 1) for the display.

      minimum: 0

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaMemoryTool20250818 object

    • type: "memory_20250818"

    • name: "memory"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolComputerUse20250124 object

    • type: "computer_20250124"

    • display_height_px: number

      The height of the display in pixels.

      minimum: 1

    • display_width_px: number

      The width of the display in pixels.

      minimum: 1

    • name: "computer"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • display_number: optional number or null

      The X11 display number (e.g. 0, 1) for the display.

      minimum: 0

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolTextEditor20241022 object

    • type: "text_editor_20241022"

    • name: "str_replace_editor"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolComputerUse20251124 object

    • type: "computer_20251124"

    • display_height_px: number

      The height of the display in pixels.

      minimum: 1

    • display_width_px: number

      The width of the display in pixels.

      minimum: 1

    • name: "computer"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • display_number: optional number or null

      The X11 display number (e.g. 0, 1) for the display.

      minimum: 0

    • enable_zoom: optional boolean

      Whether to enable an action to take a zoomed-in screenshot of the screen.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaComputerToolset20260801 object

    The computer toolset: a single tools[] entry (carrying no name) that declares the computer tool family. The model is served the family's tool with any members disabled via configs removed from its schema. Every member is enabled by default, zoom included. The single-tool options display_number and enable_zoom are not fields of a toolset entry — it carries only type, configs, and cache_control; zoom is controlled via configs.zoom.enabled.

    • type: "computer_toolset_20260801"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • configs: optional BetaComputerToolsetConfigs or null

      Per-member configuration for computer_toolset_20260801: one optional field per member tool, keyed by the member name — the same name the member's tool_use blocks carry. Every member is an accepted key, and a member's defaults apply wherever its key is absent. Unknown keys are rejected: the field set is this toolset version's complete member set.

      • type: optional BetaComputerTypeConfig or null

        type's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • cursor_position: optional BetaComputerCursorPositionConfig or null

        cursor_position's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • double_click: optional BetaComputerDoubleClickConfig or null

        double_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • hold_key: optional BetaComputerHoldKeyConfig or null

        hold_key's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • key: optional BetaComputerKeyConfig or null

        key's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_click: optional BetaComputerLeftClickConfig or null

        left_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_click_drag: optional BetaComputerLeftClickDragConfig or null

        left_click_drag's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_mouse_down: optional BetaComputerLeftMouseDownConfig or null

        left_mouse_down's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • left_mouse_up: optional BetaComputerLeftMouseUpConfig or null

        left_mouse_up's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • middle_click: optional BetaComputerMiddleClickConfig or null

        middle_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • mouse_move: optional BetaComputerMouseMoveConfig or null

        mouse_move's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • right_click: optional BetaComputerRightClickConfig or null

        right_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • screenshot: optional BetaComputerScreenshotConfig or null

        screenshot's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • scroll: optional BetaComputerScrollConfig or null

        scroll's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • triple_click: optional BetaComputerTripleClickConfig or null

        triple_click's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • wait: optional BetaComputerWaitConfig or null

        wait's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

      • zoom: optional BetaComputerZoomConfig or null

        zoom's config overrides.

        • defer_loading: optional boolean or null

          Defer loading for this member. Must resolve to the same value on every enabled member of the toolset.

        • enabled: optional boolean or null

          Whether this member is offered to the model. Default is per member, per the toolset's documentation. A member whose enabled resolves false is withheld from the served schema.

  • BetaToolTextEditor20250124 object

    • type: "text_editor_20250124"

    • name: "str_replace_editor"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolTextEditor20250429 object

    • type: "text_editor_20250429"

    • name: "str_replace_based_edit_tool"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolTextEditor20250728 object

    • type: "text_editor_20250728"

    • name: "str_replace_based_edit_tool"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • input_examples: optional array of map[unknown]

    • max_characters: optional number or null

      Maximum number of characters to display when viewing a file. If not specified, defaults to displaying the full file.

      minimum: 1

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaWebSearchTool20250305 object

    • type: "web_search_20250305"

    • name: "web_search"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      If provided, only these domains will be included in results. Cannot be used alongside blocked_domains.

    • blocked_domains: optional array of string or null

      If provided, these domains will never appear in results. Cannot be used alongside allowed_domains.

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • user_location: optional BetaUserLocation or null

      Parameters for the user's location. Used to provide more relevant search results.

      • type: "approximate"

      • city: optional string or null

        The city of the user.

        maxLength: 255, minLength: 1

      • country: optional string or null

        The two letter ISO country code of the user.

        maxLength: 2, minLength: 2

      • region: optional string or null

        The region of the user.

        maxLength: 255, minLength: 1

      • timezone: optional string or null

        The IANA timezone of the user.

        maxLength: 255, minLength: 1

  • BetaWebFetchTool20250910 object

    • type: "web_fetch_20250910"

    • name: "web_fetch"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      List of domains to allow fetching from

    • blocked_domains: optional array of string or null

      List of domains to block fetching from

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam or null

      Citations configuration for fetched documents. Citations are disabled by default.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_content_tokens: optional number or null

      Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      exclusiveMinimum: 0

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • url_sources: optional BetaWebFetchURLSources or null

      Which sources contribute to the set of URLs web fetch may fetch.

      Each key is a tagged variant: user_input is all or none; the two tool filters are all, none, only (only the named tools' results) or except (every result but the named tools'). A named tool must be declared in this request's tools[].

      • client_tool_results: optional BetaWebFetchURLSourceAll or BetaWebFetchURLSourceNone or BetaWebFetchURLSourceOnly or BetaWebFetchURLSourceExcept

        Which client tools' results contribute fetchable URLs: "all", "none", or an only or except list of client tool names from tools[].

        • BetaWebFetchURLSourceAll object

          The url_sources variant under which a source contributes in full: every result of the tool filter's source, or all user input.

          • type: "all"

        • BetaWebFetchURLSourceNone object

          The url_sources variant under which a source contributes nothing: no result of the tool filter's source, or no user input.

          • type: "none"

        • BetaWebFetchURLSourceOnly object

          The tool filter variant under which only the named tools' results contribute.

          • type: "only"

          • tools: array of BetaWebFetchURLSourceToolReference

            • type: "tool_reference"

            • name: string

        • BetaWebFetchURLSourceExcept object

          The tool filter variant under which every result but the named tools' contributes.

          • type: "except"

          • tools: array of BetaWebFetchURLSourceToolReference

            • type: "tool_reference"

            • name: string

      • server_tool_results: optional BetaWebFetchURLSourceAll or BetaWebFetchURLSourceNone or BetaWebFetchURLSourceOnly or BetaWebFetchURLSourceExcept

        Which server tools' results contribute fetchable URLs: "all", "none", or an only or except list of server tool names from tools[]; only web_search and web_fetch results ever contribute.

        • BetaWebFetchURLSourceAll object

          The url_sources variant under which a source contributes in full: every result of the tool filter's source, or all user input.

        • BetaWebFetchURLSourceNone object

          The url_sources variant under which a source contributes nothing: no result of the tool filter's source, or no user input.

        • BetaWebFetchURLSourceOnly object

          The tool filter variant under which only the named tools' results contribute.

        • BetaWebFetchURLSourceExcept object

          The tool filter variant under which every result but the named tools' contributes.

      • user_input: optional BetaWebFetchURLSourceAll or BetaWebFetchURLSourceNone

        Whether URLs in user messages are fetchable: "all" or "none".

        • BetaWebFetchURLSourceAll object

          The url_sources variant under which a source contributes in full: every result of the tool filter's source, or all user input.

        • BetaWebFetchURLSourceNone object

          The url_sources variant under which a source contributes nothing: no result of the tool filter's source, or no user input.

  • BetaWebSearchTool20260209 object

    • type: "web_search_20260209"

    • name: "web_search"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      If provided, only these domains will be included in results. Cannot be used alongside blocked_domains.

    • blocked_domains: optional array of string or null

      If provided, these domains will never appear in results. Cannot be used alongside allowed_domains.

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • user_location: optional BetaUserLocation or null

      Parameters for the user's location. Used to provide more relevant search results.

  • BetaWebFetchTool20260209 object

    • type: "web_fetch_20260209"

    • name: "web_fetch"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      List of domains to allow fetching from

    • blocked_domains: optional array of string or null

      List of domains to block fetching from

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam or null

      Citations configuration for fetched documents. Citations are disabled by default.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_content_tokens: optional number or null

      Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      exclusiveMinimum: 0

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • url_sources: optional BetaWebFetchURLSources or null

      Which sources contribute to the set of URLs web fetch may fetch.

      Each key is a tagged variant: user_input is all or none; the two tool filters are all, none, only (only the named tools' results) or except (every result but the named tools'). A named tool must be declared in this request's tools[].

  • BetaWebFetchTool20260309 object

    Web fetch tool with use_cache parameter for bypassing cached content.

    • type: "web_fetch_20260309"

    • name: "web_fetch"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      List of domains to allow fetching from

    • blocked_domains: optional array of string or null

      List of domains to block fetching from

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam or null

      Citations configuration for fetched documents. Citations are disabled by default.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_content_tokens: optional number or null

      Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      exclusiveMinimum: 0

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • url_sources: optional BetaWebFetchURLSources or null

      Which sources contribute to the set of URLs web fetch may fetch.

      Each key is a tagged variant: user_input is all or none; the two tool filters are all, none, only (only the named tools' results) or except (every result but the named tools'). A named tool must be declared in this request's tools[].

    • use_cache: optional boolean

      Whether to use cached content. Set to false to bypass the cache and fetch fresh content. Only set to false when the user explicitly requests fresh content or when fetching rapidly-changing sources.

  • BetaWebSearchTool20260318 object

    • type: "web_search_20260318"

    • name: "web_search"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      If provided, only these domains will be included in results. Cannot be used alongside blocked_domains.

    • blocked_domains: optional array of string or null

      If provided, these domains will never appear in results. Cannot be used alongside allowed_domains.

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • response_inclusion: optional "full" or "excluded"

      How this tool's result blocks appear in the API response when the result was consumed by a completed code_execution call in the same turn. 'full' returns the complete content (default). 'excluded' drops the nested server_tool_use and result block pair entirely. Results from direct calls, or from code_execution calls that paused before completing, are always returned in full so they can be sent back on the next turn.

      • "full"

      • "excluded"

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • user_location: optional BetaUserLocation or null

      Parameters for the user's location. Used to provide more relevant search results.

  • BetaWebFetchTool20260318 object

    • type: "web_fetch_20260318"

    • name: "web_fetch"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • allowed_domains: optional array of string or null

      List of domains to allow fetching from

    • blocked_domains: optional array of string or null

      List of domains to block fetching from

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • citations: optional BetaCitationsConfigParam or null

      Citations configuration for fetched documents. Citations are disabled by default.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_content_tokens: optional number or null

      Maximum number of tokens used by including web page text content in the context. The limit is approximate and does not apply to binary content such as PDFs.

      exclusiveMinimum: 0

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • response_inclusion: optional "full" or "excluded"

      How this tool's result blocks appear in the API response when the result was consumed by a completed code_execution call in the same turn. 'full' returns the complete content (default). 'excluded' drops the nested server_tool_use and result block pair entirely. Results from direct calls, or from code_execution calls that paused before completing, are always returned in full so they can be sent back on the next turn.

      • "full"

      • "excluded"

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

    • url_sources: optional BetaWebFetchURLSources or null

      Which sources contribute to the set of URLs web fetch may fetch.

      Each key is a tagged variant: user_input is all or none; the two tool filters are all, none, only (only the named tools' results) or except (every result but the named tools'). A named tool must be declared in this request's tools[].

    • use_cache: optional boolean

      Whether to use cached content. Set to false to bypass the cache and fetch fresh content. Only set to false when the user explicitly requests fresh content or when fetching rapidly-changing sources.

  • BetaAdvisorTool20260301 object

    • type: "advisor_20260301"

    • model: Model

      The model that will complete your prompt.

      See models for additional details and options.

    • name: "advisor"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • caching: optional BetaCacheControlEphemeral or null

      Caching for the advisor's own prompt. When set, each advisor call writes a cache entry at the given TTL so subsequent calls in the same conversation read the stable prefix. When omitted, the advisor prompt is not cached.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • max_tokens: optional number or null

      Bounds the advisor's total output (thinking + text) per call. When the advisor hits this cap, the returned advisor_result or advisor_redacted_result block carries stop_reason='max_tokens', and a truncation note is appended to the advice text the worker model sees (inside the encrypted blob in redacted mode). When set, the server also emits a remaining-tokens budget block in the advisor's prompt so the advisor self-shapes toward the cap. When omitted, the advisor model's default output cap applies and no budget block is emitted.

      minimum: 1024

    • max_uses: optional number or null

      Maximum number of times the tool can be used in the API request.

      exclusiveMinimum: 0

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolSearchToolBm25_20251119 object

    • type: "tool_search_tool_bm25_20251119" or "tool_search_tool_bm25"

      • "tool_search_tool_bm25_20251119"

      • "tool_search_tool_bm25"

    • name: "tool_search_tool_bm25"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaToolSearchToolRegex20251119 object

    • type: "tool_search_tool_regex_20251119" or "tool_search_tool_regex"

      • "tool_search_tool_regex_20251119"

      • "tool_search_tool_regex"

    • name: "tool_search_tool_regex"

      Name of the tool.

      This is how the tool will be called by the model and in tool_use blocks.

    • allowed_callers: optional array of "direct" or "code_execution_20250825" or "code_execution_20260120" or "code_execution_20260521"

      • "direct"

      • "code_execution_20250825"

      • "code_execution_20260120"

      • "code_execution_20260521"

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • defer_loading: optional boolean

      If true, tool will not be included in initial system prompt. Only loaded when returned via tool_reference from tool search.

    • strict: optional boolean

      When true, guarantees schema validation on tool names and inputs

  • BetaMCPToolset object

    Configuration for a group of tools from an MCP server.

    Allows configuring enabled status and defer_loading for all tools from an MCP server, with optional per-tool overrides.

    • type: "mcp_toolset"

    • mcp_server_name: string

      Name of the MCP server to configure tools for

      maxLength: 255, minLength: 1

    • cache_control: optional BetaCacheControlEphemeral or null

      Create a cache control breakpoint at this content block.

    • configs: optional map[BetaMCPToolConfig] or null

      Configuration overrides for specific tools, keyed by tool name

      • defer_loading: optional boolean

      • enabled: optional boolean

    • default_config: optional BetaMCPToolDefaultConfig

      Default configuration applied to all tools from this server

      • defer_loading: optional boolean

      • enabled: optional boolean

• output_format: optional BetaJSONOutputFormat or null

  Deprecated

  Deprecated: Use output_config.format instead. See structured outputs

  A schema to specify Claude's output format in responses. This parameter will be removed in a future release.

• temperature: optional number

  Deprecated: Deprecated. Models released after Claude Opus 4.6 do not support setting temperature. A value of 1.0 will be accepted for backwards compatibility, all other values will be rejected with a 400 error.

  Amount of randomness injected into the response.

  Defaults to 1.0. Ranges from 0.0 to 1.0. Use temperature closer to 0.0 for analytical / multiple choice, and closer to 1.0 for creative and generative tasks.

  Note that even with temperature of 0.0, the results will not be fully deterministic.

  maximum: 1, minimum: 0

• top_k: optional number

  Deprecated: Deprecated. Models released after Claude Opus 4.6 do not accept top_k; any value will be rejected with a 400 error.

  Only sample from the top K options for each subsequent token.

  Used to remove "long tail" low probability responses. Learn more technical details here.

  Recommended for advanced use cases only.

  minimum: 0

• top_p: optional number

  Deprecated: Deprecated. Models released after Claude Opus 4.6 do not support setting top_p. A value >= 0.99 will be accepted for backwards compatibility, all other values will be rejected with a 400 error.

  Use nucleus sampling.

  In nucleus sampling, we compute the cumulative distribution over all the options for each subsequent token in decreasing probability order and cut it off once it reaches a particular probability specified by top_p.

  Recommended for advanced use cases only.

  maximum: 1, minimum: 0

# Returns

• BetaMessage object

  • type: "message"

    Object type.

    For Messages, this is always "message".

    default: message

  • id: string

    Unique object identifier.

    The format and length of IDs may change over time.

  • container: BetaContainer or null

    Information about the container used in the request (for the code execution tool)

    • id: string

      Identifier for the container used in this request

    • expires_at: string

      The time at which the container will expire.

      format: date-time

    • skills: array of BetaContainerSkill or null

      Skills loaded in the container

      • type: "anthropic" or "custom"

        Type of skill - either 'anthropic' (built-in) or 'custom' (user-defined)

        • "anthropic"

        • "custom"

      • skill_id: string

        Skill ID

        maxLength: 64, minLength: 1

      • version: string

        The resolved version: a skill version ID for custom skills.

        maxLength: 64, minLength: 1

  • content: array of BetaContentBlock

    Content generated by the model.

    This is an array of content blocks, each of which has a type that determines its shape.

    Example:

    jsonCopy

    [{"type": "text", "text": "Hi, I'm Claude."}]

    If the request input messages ended with an assistant turn, then the response content will continue directly from that last turn. You can use this to constrain the model's output.

    For example, if the input messages were:

    jsonCopy

    [
      {"role": "user", "content": "What's the Greek name for Sun? (A) Sol (B) Helios (C) Sun"},
      {"role": "assistant", "content": "The best answer is ("}
    ]

    Then the response content might be:

    jsonCopy

    [{"type": "text", "text": "B)"}]

    • BetaTextBlock object

      • type: "text"

        default: text

      • citations: array of BetaTextCitation or null

        Citations supporting the text block.

        The type of citation returned will depend on the type of document being cited. Citing a PDF results in page_location, plain text results in char_location, and content document results in content_block_location.

        • BetaCitationCharLocation object

          • type: "char_location"

            default: char_location

          • cited_text: string

          • document_index: number

            minimum: 0

          • document_title: string or null

          • end_char_index: number

          • file_id: string or null

          • start_char_index: number

            minimum: 0

        • BetaCitationPageLocation object

          • type: "page_location"

            default: page_location

          • cited_text: string

          • document_index: number

            minimum: 0

          • document_title: string or null

          • end_page_number: number

          • file_id: string or null

          • start_page_number: number

            minimum: 1

        • BetaCitationContentBlockLocation object

          • type: "content_block_location"

            default: content_block_location

          • cited_text: string

            The full text of the cited block range, concatenated.

            Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

          • document_index: number

            minimum: 0

          • document_title: string or null

          • end_block_index: number

            Exclusive 0-based end index of the cited block range in the source's content array.

            Always greater than start_block_index; a single-block citation has end_block_index = start_block_index + 1.

          • file_id: string or null

          • start_block_index: number

            0-based index of the first cited block in the source's content array.

            minimum: 0

        • BetaCitationsWebSearchResultLocation object

          • type: "web_search_result_location"

            default: web_search_result_location

          • cited_text: string

          • encrypted_index: string

          • title: string or null

            maxLength: 512

          • url: string

        • BetaCitationSearchResultLocation object

          • type: "search_result_location"

            default: search_result_location

          • cited_text: string

            The full text of the cited block range, concatenated.

            Always equals the contents of content[start_block_index:end_block_index] joined together. The text block is the minimal citable unit; this field is never a substring of a single block. Not counted toward output tokens, and not counted toward input tokens when sent back in subsequent turns.

          • end_block_index: number

            Exclusive 0-based end index of the cited block range in the source's content array.

            Always greater than start_block_index; a single-block citation has end_block_index = start_block_index + 1.

          • search_result_index: number

            0-based index of the cited search result among all search_result content blocks in the request, in the order they appear across messages and tool results.

            Counted separately from document_index; server-side web search results are not included in this count.

            minimum: 0

          • source: string

          • start_block_index: number

            0-based index of the first cited block in the source's content array.

            minimum: 0

          • title: string or null

      • text: string

        minLength: 0

    • BetaThinkingBlock object

      • type: "thinking"

        default: thinking

      • signature: string

        A value used to verify that this thinking block was generated by Claude when it is passed back to the API.

        This is an opaque field and should not be interpreted or parsed. When passing thinking blocks back to the API (required when using tools with extended thinking), pass them back exactly as received, with this field intact.

        See extended thinking for details.

      • thinking: string

        The text of Claude's thinking process for this block.

    • BetaRedactedThinkingBlock object

      • type: "redacted_thinking"

        default: redacted_thinking

      • data: string

        The contents of this redacted thinking block, returned when portions of the model's thinking were safety-redacted. This field is opaque and encrypted, with no readable content.

        Pass redacted_thinking blocks back to the API unchanged when continuing a multi-turn conversation.

        See extended thinking for details.

    • BetaToolUseBlock object

      • type: "tool_use"

        default: tool_use

      • id: string

        pattern: ^[23]+$

      • input: map[unknown]

      • name: string

        minLength: 1

      • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

        • BetaDirectCaller object

          Tool invocation directly from the model.

          • type: "direct"

        • BetaServerToolCaller object

          Tool invocation generated by a server-side tool.

          • type: "code_execution_20250825"

          • tool_id: string

            pattern: ^srvtoolu_[a-zA-Z0-9_]+$

        • BetaServerToolCaller20260120 object

          • type: "code_execution_20260120"

          • tool_id: string

            pattern: ^srvtoolu_[a-zA-Z0-9_]+$

      • toolset_name: optional string or null

        For a toolset member tool_use, the toolset family.

        maxLength: 64, minLength: 1, pattern: ^[24]+$

    • BetaServerToolUseBlock object

      • type: "server_tool_use"

        default: server_tool_use

      • id: string

        pattern: ^srvtoolu_[a-zA-Z0-9_]+$

      • input: map[unknown]

      • name: "advisor" or "web_search" or "web_fetch" or 5 more

        • "advisor"

        • "web_search"

        • "web_fetch"

        • "code_execution"

        • "bash_code_execution"

        • "text_editor_code_execution"

        • "tool_search_tool_regex"

        • "tool_search_tool_bm25"

      • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

        • BetaDirectCaller object

          Tool invocation directly from the model.

        • BetaServerToolCaller object

          Tool invocation generated by a server-side tool.

        • BetaServerToolCaller20260120 object

    • BetaWebSearchToolResultBlock object

      • type: "web_search_tool_result"

        default: web_search_tool_result

      • content: BetaWebSearchToolResultBlockContent

        • BetaWebSearchToolResultError object

          • type: "web_search_tool_result_error"

            default: web_search_tool_result_error

          • error_code: BetaWebSearchToolResultErrorCode

            • "invalid_tool_input"

            • "unavailable"

            • "max_uses_exceeded"

            • "too_many_requests"

            • "query_too_long"

            • "request_too_large"

        • array of BetaWebSearchResultBlock

          • type: "web_search_result"

            default: web_search_result

          • encrypted_content: string

          • page_age: string or null

          • title: string

          • url: string

      • tool_use_id: string

        pattern: ^srvtoolu_[a-zA-Z0-9_]+$

      • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

        • BetaDirectCaller object

          Tool invocation directly from the model.

        • BetaServerToolCaller object

          Tool invocation generated by a server-side tool.

        • BetaServerToolCaller20260120 object

    • BetaWebFetchToolResultBlock object

      • type: "web_fetch_tool_result"

        default: web_fetch_tool_result

      • content: BetaWebFetchToolResultErrorBlock or BetaWebFetchBlock

        • BetaWebFetchToolResultErrorBlock object

          • type: "web_fetch_tool_result_error"

            default: web_fetch_tool_result_error

          • error_code: BetaWebFetchToolResultErrorCode

            • "invalid_tool_input"

            • "url_too_long"

            • "url_not_allowed"

            • "url_not_in_prior_context"

            • "url_not_accessible"

            • "unsupported_content_type"

            • "too_many_requests"

            • "max_uses_exceeded"

            • "unavailable"

            • "content_too_large"

        • BetaWebFetchBlock object

          • type: "web_fetch_result"

            default: web_fetch_result

          • content: BetaDocumentBlock

            • type: "document"

              default: document

            • citations: BetaCitationConfig or null

              Citation configuration for the document

              • enabled: boolean

                default: false

            • source: BetaBase64PDFSource or BetaPlainTextSource

              • BetaBase64PDFSource object

                • type: "base64"

                • data: string

                  format: byte

                • media_type: "application/pdf"

              • BetaPlainTextSource object

                • type: "text"

                • data: string

                • media_type: "text/plain"

            • title: string or null

              The title of the document

          • retrieved_at: string or null

            ISO 8601 timestamp when the content was retrieved

          • url: string

            Fetched content URL

      • tool_use_id: string

        pattern: ^srvtoolu_[a-zA-Z0-9_]+$

      • caller: optional BetaDirectCaller or BetaServerToolCaller or BetaServerToolCaller20260120

        • BetaDirectCaller object

          Tool invocation directly from the model.

        • BetaServerToolCaller object

          Tool invocation generated by a server-side tool.

        • BetaServerToolCaller20260120 object

    • BetaAdvisorToolResultBlock object

      • type: "advisor_tool_result"

        default: advisor_tool_result

      • content: BetaAdvisorToolResultError or BetaAdvisorResultBlock or BetaAdvisorRedactedResultBlock

        • BetaAdvisorToolResultError object

          • type: "advisor_tool_result_error"

            default: advisor_tool_result_error

          • error_code: "max_uses_exceeded" or "prompt_too_long" or "too_many_requests" or 4 more

            • "max_uses_exceeded"

            • "prompt_too_long"

            • "too_many_requests"

            • "overloaded"

            • "unavailable"

            • "execution_time_exceeded"

            • "model_not_found"

        • BetaAdvisorResultBlock object

          • type: "advisor_result"

            default: advisor_result

          • stop_reason: string or null

            The advisor sub-inference's stop reason (same values as the top-level message stop_reason). max_tokens indicates the advisor's output was truncated at the tool's max_tokens value or the advisor model's policy cap.

          • text: string

        • BetaAdvisorRedactedResultBlock object

          • type: "advisor_redacted_result"

            default: advisor_redacted_result

          • encrypted_content: string

            Opaque blob containing the advisor's output. Round-trip verbatim; do not inspect or modify.

          • stop_reason: string or null

            The advisor sub-inference's stop reason (same values as the top-level message stop_reason).

      • tool_use_id: string

        pattern: ^srvtoolu_[a-zA-Z0-9_]+$

    • BetaCodeExecutionToolResultBlock object

      • type: "code_execution_tool_result"

        default: code_execution_tool_result

      • content: BetaCodeExecutionToolResultBlockContent

        • BetaCodeExecutionToolResultError object

          • type: "code_execution_tool_result_error"

            default: code_execution_tool_result_error

          • error_code: BetaCodeExecutionToolResultErrorCode

            • "invalid_tool_input"

            • "unavailable"

            • "too_many_requests"

            • "execution_time_exceeded"

        • BetaCodeExecutionResultBlock object

          • type: "code_execution_result"

            default: code_execution_result

          • content: array of BetaCodeExecutionOutputBlock

            • type: "code_execution_output"

              default: code_execution_output

            • file_id: string

          • return_code: number

          • stderr: string

          • stdout: string

        • BetaEncryptedCodeExecutionResultBlock object

          Code execution result with encrypted stdout for PFC + web_search results.

          • type: "encrypted_code_execution_result"

            default: encrypted_code_execution_result

          • content: array of BetaCodeExecutionOutputBlock

            • type: "code_execution_output"

              default: code_execution_output

            • file_id: string

          • encrypted_stdout: string

          • return_code: number

          • stderr: string

      • tool_use_id: string

        pattern: ^srvtoolu_[a-zA-Z0-9_]+$

    • BetaBashCodeExecutionToolResultBlock object

      • type: "bash_code_execution_tool_result"

        default: bash_code_execution_tool_result

      • content: BetaBashCodeExecutionToolResultError or BetaBashCodeExecutionResultBlock

        • BetaBashCodeExecutionToolResultError object

          • type: "bash_code_execution_tool_result_error"

            default: bash_code_execution_tool_result_error

          • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or 2 more

            • "invalid_tool_input"

            • "unavailable"

            • "too_many_requests"

            • "execution_time_exceeded"

            • "output_file_too_large"

        • BetaBashCodeExecutionResultBlock object

          • type: "bash_code_execution_result"

            default: bash_code_execution_result

          • content: array of BetaBashCodeExecutionOutputBlock

            • type: "bash_code_execution_output"

              default: bash_code_execution_output

            • file_id: string

          • return_code: number

          • stderr: string

          • stdout: string

      • tool_use_id: string

        pattern: ^srvtoolu_[a-zA-Z0-9_]+$

    • BetaTextEditorCodeExecutionToolResultBlock object

      • type: "text_editor_code_execution_tool_result"

        default: text_editor_code_execution_tool_result

      • content: BetaTextEditorCodeExecutionToolResultError or BetaTextEditorCodeExecutionViewResultBlock or BetaTextEditorCodeExecutionCreateResultBlock or BetaTextEditorCodeExecutionStrReplaceResultBlock

        • BetaTextEditorCodeExecutionToolResultError object

          • type: "text_editor_code_execution_tool_result_error"

            default: text_editor_code_execution_tool_result_error

          • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or 2 more

            • "invalid_tool_input"

            • "unavailable"

            • "too_many_requests"

            • "execution_time_exceeded"

            • "file_not_found"

          • error_message: string or null

        • BetaTextEditorCodeExecutionViewResultBlock object

          • type: "text_editor_code_execution_view_result"

            default: text_editor_code_execution_view_result

          • content: string

          • file_type: "text" or "image" or "pdf"

            • "text"

            • "image"

            • "pdf"

          • num_lines: number or null

          • start_line: number or null

          • total_lines: number or null

        • BetaTextEditorCodeExecutionCreateResultBlock object

          • type: "text_editor_code_execution_create_result"

            default: text_editor_code_execution_create_result

          • is_file_update: boolean

        • BetaTextEditorCodeExecutionStrReplaceResultBlock object

          • type: "text_editor_code_execution_str_replace_result"

            default: text_editor_code_execution_str_replace_result

          • lines: array of string or null

          • new_lines: number or null

          • new_start: number or null

          • old_lines: number or null

          • old_start: number or null

      • tool_use_id: string

        pattern: ^srvtoolu_[a-zA-Z0-9_]+$

    • BetaToolSearchToolResultBlock object

      • type: "tool_search_tool_result"

        default: tool_search_tool_result

      • content: BetaToolSearchToolResultError or BetaToolSearchToolSearchResultBlock

        • BetaToolSearchToolResultError object

          • type: "tool_search_tool_result_error"

            default: tool_search_tool_result_error

          • error_code: "invalid_tool_input" or "unavailable" or "too_many_requests" or "execution_time_exceeded"

            • "invalid_tool_input"

            • "unavailable"

            • "too_many_requests"

            • "execution_time_exceeded"

          • error_message: string or null

        • BetaToolSearchToolSearchResultBlock object

          • type: "tool_search_tool_search_result"

            default: tool_search_tool_search_result

          • tool_references: array of BetaToolReferenceBlock

            • type: "tool_reference"

              default: tool_reference

            • tool_name: string

              maxLength: 256, minLength: 1, pattern: ^[25]{1,256}$

      • tool_use_id: string

        pattern: ^srvtoolu_[a-zA-Z0-9_]+$

    • BetaMCPToolUseBlock object

      • type: "mcp_tool_use"

        default: mcp_tool_use

      • id: string

        pattern: ^[26]+$

      • input: map[unknown]

      • name: string

        The name of the MCP tool

      • server_name: string

        The name of the MCP server

    • BetaMCPToolResultBlock object

      • type: "mcp_tool_result"

        default: mcp_tool_result

      • content: string or array of BetaTextBlock

        • string

        • BetaMCPToolResultBlockContent = array of BetaTextBlock

          • type: "text"

            default: text

          • citations: array of BetaTextCitation or null

            Citations supporting the text block.

            The type of citation returned will depend on the type of document being cited. Citing a PDF results in page_location, plain text results in char_location, and content document results in content_block_location.

          • text: string

            minLength: 0

      • is_error: boolean

        default: false

      • tool_use_id: string

        pattern: ^[27]+$

    • BetaContainerUploadBlock object

      Response model for a file uploaded to the container.

      • type: "container_upload"

        default: container_upload

      • file_id: string

    • BetaCompactionBlock object

      A compaction block returned when autocompact is triggered.

      When content is None, it indicates the compaction failed to produce a valid summary (e.g., malformed output from the model). Clients may round-trip compaction blocks with null content; the server treats them as no-ops.

      • type: "compaction"

        default: compaction

      • content: string or null

        Summary of compacted content, or null if compaction failed

      • encrypted_content: string or null

        Opaque metadata from prior compaction, to be round-tripped verbatim

      • signature: optional string or null

        Signature over the summary, to be sent back with the block verbatim

    • BetaFallbackBlock object

      Marks the point in content where one model's output gives way to the next.

      One block appears per hop where a preceding model actually ran this turn and declined. A turn where no preceding model ran and declined has no such boundary and carries no block — the signal for whether a fallback model served the response is the presence of a fallback_message entry in usage.iterations, not this block.

      The block is treated like a server-tool content block for streaming: it arrives via the standard content_block_start / content_block_stop pair and carries no deltas.

      • type: "fallback"

        default: fallback

      • from: BetaFallbackInfo

        The model whose output ends at this point — the model that declined at this hop. When the declining hop is the requested model, its model echoes the top-level model string the caller sent (alias or canonical); when the declining hop is a fallback model, its model is that model's canonical id.

        • model: Model

          The model that will complete your prompt.

          See models for additional details and options.

          • "claude-fable-5-1" or "claude-mythos-5-1" or "claude-sonnet-5" or 14 more

            The model that will complete your prompt.

            See models for additional details and options.

            • "claude-fable-5-1"

              Frontier intelligence for ambitious tasks across coding, scientific discovery, and enterprise workflows

            • "claude-mythos-5-1"

              Our most capable model for cybersecurity and biology research, available through trusted access programs

            • "claude-sonnet-5"

              High-performance model for coding and agents

            • "claude-fable-5"

              Next generation of intelligence for the hardest knowledge work and coding problems

            • "claude-mythos-5"

              Most capable model for cybersecurity and biology research

            • "claude-opus-5"

              Powerful intelligence for long-running agents and coding

            • "claude-opus-4-8"

              Powerful intelligence for long-running agents and coding

            • "claude-opus-4-7"

              Powerful intelligence for long-running agents and coding

            • "claude-mythos-preview"

              New class of intelligence, strongest in coding and cybersecurity

            • "claude-opus-4-6"

              Powerful intelligence for long-running agents and coding

            • "claude-sonnet-4-6"

              Best combination of speed and intelligence

            • "claude-haiku-4-5"

              Fastest model with near-frontier intelligence

            • "claude-haiku-4-5-20251001"

              Fastest model with near-frontier intelligence

            • "claude-opus-4-5"

              Powerful intelligence for long-running agents and coding

            • "claude-opus-4-5-20251101"

              Powerful intelligence for long-running agents and coding

            • "claude-sonnet-4-5"

              High-performance model for agents and coding

            • "claude-sonnet-4-5-20250929"

              High-performance model for agents and coding

          • string

      • to: BetaFallbackInfo

        The fallback model producing the content that follows this block. Its model is always the canonical id.

      • trigger: BetaFallbackRefusalTrigger

        What caused the from model to hand over at this hop.

        • type: "refusal"

          default: refusal

        • category: "cyber" or "bio" or "frontier_llm" or 2 more or null

          The policy category that triggered a refusal.

          • "cyber"

            The request could enable cyber harm, such as malware or exploit development. Benign cybersecurity work can also trigger this category.

          • "bio"

            The request could enable biological harm, such as dangerous lab methods. Beneficial life sciences work can also trigger this category.

          • "frontier_llm"

            The request could assist the development of competing AI models, which is restricted under Anthropic's commercial terms. Benign machine learning work can also trigger this category.

          • "reasoning_extraction"

            The request asks the model to reproduce its internal reasoning in the response text. To get reasoning in a structured form instead, use adaptive thinking.

          • "general_harms"

            The request could be related to an area that was determined as harmful. Benign work might sometimes trigger this category.

  • context_management: BetaContextManagementResponse or null

    Context management response.

    Information about context management strategies applied during the request.

    • applied_edits: array of BetaClearToolUses20250919EditResponse or BetaClearThinking20251015EditResponse

      List of context management edits that were applied.

      • BetaClearToolUses20250919EditResponse object

        • type: "clear_tool_uses_20250919"

          The type of context management edit applied.

          default: clear_tool_uses_20250919

        • cleared_input_tokens: number

          Number of input tokens cleared by this edit.

          minimum: 0

        • cleared_tool_uses: number

          Number of tool uses that were cleared.

          minimum: 0

      • BetaClearThinking20251015EditResponse object

        • type: "clear_thinking_20251015"

          The type of context management edit applied.

          default: clear_thinking_20251015

        • cleared_input_tokens: number

          Number of input tokens cleared by this edit.

          minimum: 0

        • cleared_thinking_turns: number

          Number of thinking turns that were cleared.

          minimum: 0

  • diagnostics: BetaDiagnostics or null

    Response envelope for request-level diagnostics. Present (possibly null) whenever the caller supplied diagnostics on the request.

    • cache_miss_reason: BetaCacheMissModelChanged or BetaCacheMissSystemChanged or BetaCacheMissToolsChanged or 3 more or null

      Explains why the prompt cache could not fully reuse the prefix from the request identified by diagnostics.previous_message_id. null means diagnosis is still pending — the response was serialized before the background comparison completed.

      • BetaCacheMissModelChanged object

        • type: "model_changed"

          default: model_changed

        • cache_missed_input_tokens: number

          Approximate number of input tokens that would have been read from cache had the prefix matched the previous request.

      • BetaCacheMissSystemChanged object

        • type: "system_changed"

          default: system_changed

        • cache_missed_input_tokens: number

          Approximate number of input tokens that would have been read from cache had the prefix matched the previous request.

      • BetaCacheMissToolsChanged object

        • type: "tools_changed"

          default: tools_changed

        • cache_missed_input_tokens: number

          Approximate number of input tokens that would have been read from cache had the prefix matched the previous request.

      • BetaCacheMissMessagesChanged object

        • type: "messages_changed"

          default: messages_changed

        • cache_missed_input_tokens: number

          Approximate number of input tokens that would have been read from cache had the prefix matched the previous request.

      • BetaCacheMissPreviousMessageNotFound object

        • type: "previous_message_not_found"

          default: previous_message_not_found

      • BetaCacheMissUnavailable object

        • type: "unavailable"

          default: unavailable

  • model: Model

    The model that will complete your prompt.

    See models for additional details and options.

  • role: "assistant"

    Conversational role of the generated message.

    This will always be "assistant".

    default: assistant

  • stop_details: BetaRefusalStopDetails or null

    Structured information about a refusal.

    • type: "refusal"

      default: refusal

    • category: "cyber" or "bio" or "frontier_llm" or 2 more or null

      The policy category that triggered a refusal.

      • "cyber"

        The request could enable cyber harm, such as malware or exploit development. Benign cybersecurity work can also trigger this category.

      • "bio"

        The request could enable biological harm, such as dangerous lab methods. Beneficial life sciences work can also trigger this category.

      • "frontier_llm"

        The request could assist the development of competing AI models, which is restricted under Anthropic's commercial terms. Benign machine learning work can also trigger this category.

      • "reasoning_extraction"

        The request asks the model to reproduce its internal reasoning in the response text. To get reasoning in a structured form instead, use adaptive thinking.

      • "general_harms"

        The request could be related to an area that was determined as harmful. Benign work might sometimes trigger this category.

    • explanation: string or null

      Human-readable explanation of the refusal.

      This text is not guaranteed to be stable. null when no explanation is available for the category.

    • fallback_credit_token: string or null

      Opaque code that refunds the cache-miss cost when retrying this refused request on the fallback model. Pass it as fallback_credit_token on the retry request. Expires 5 minutes after the refusal.

      The retry is sent either with the same request body (system, messages, tools, and other render-shaping fields), or with the same body plus one appended assistant message whose content is the partial text (with any trailing whitespace stripped from the final text block) and paired server-tool blocks from this refusal — which also authorizes that appended turn as an assistant-prefill continuation on models that otherwise disallow prefill. A token minted mid-server-tool-loop whose partial content was continuable may only be redeemed the second way — if a same-body retry is rejected with a 400 saying the token must be redeemed by continuing the partial response, retry the second way instead. Either way: same workspace, same platform; a mismatch is a 400. Resending a token for an already-warm prefix is permitted but yields no additional credit.

      null when the refused model isn't eligible for a fallback credit.

    • fallback_has_prefill_claim: boolean or null

      Whether the accompanying fallback_credit_token may be redeemed with the appended-assistant retry form. Only set when fallback_credit_token is present.

      true: retry by resending the same request body plus one appended assistant message whose content is this response's content with any trailing whitespace stripped from the final text block and unpaired tool_use blocks omitted (the same appended-turn shape described on fallback_credit_token), with the token attached. false: retry by resending the original request body unchanged, with the token attached — the appended-assistant form is not available for this refusal (no continuable partial content, or the request uses output_format or a tool_choice that forces tool use). One exception: when the request used output_format or a forced tool_choice and the refusal arrived after server tools (including MCP connector tools) had already executed, the token may not be redeemable by either retry form; if the exact-body retry is then rejected with a 400 saying the token must be redeemed by continuing the partial response, discard the token and retry without it.

      Advisory: if an appended-assistant retry is rejected with a 400 despite true, fall back to resending the original request body with the token.

    • recommended_model: string or null

      The server's suggested retry target for this refusal. Populated when a fallback attempt could not be made (the fallback model's rate limit was exhausted, or it was overloaded); names the fallback model the caller can retry directly. Null otherwise.

  • stop_reason: BetaStopReason or null

    The reason that we stopped.

    This may be one the following values:

    • "end_turn": the model reached a natural stopping point
    • "max_tokens": we exceeded the requested max_tokens or the model's maximum
    • "stop_sequence": one of your provided custom stop_sequences was generated
    • "tool_use": the model invoked one or more tools
    • "pause_turn": we paused a long-running turn. You may provide the response back as-is in a subsequent request to let the model continue.
    • "refusal": when streaming classifiers intervene to handle potential policy violations
    • "model_context_window_exceeded": we exceeded the model's context window

    In non-streaming mode this value is always non-null. In streaming mode, it is null in the message_start event and non-null otherwise.

    • "end_turn"

    • "max_tokens"

    • "stop_sequence"

    • "tool_use"

    • "pause_turn"

    • "compaction"

    • "refusal"

    • "model_context_window_exceeded"

  • stop_sequence: string or null

    Which custom stop sequence was generated, if any.

    This value will be a non-null string if one of your custom stop sequences was generated.

  • usage: BetaUsage

    Billing and rate-limit usage.

    Anthropic's API bills and rate-limits by token counts, as tokens represent the underlying cost to our systems.

    Under the hood, the API transforms requests into a format suitable for the model. The model's output then goes through a parsing stage before becoming an API response. As a result, the token counts in usage will not match one-to-one with the exact visible content of an API request or response.

    For example, output_tokens will be non-zero, even for an empty string response from Claude.

    Total input tokens in a request is the summation of input_tokens, cache_creation_input_tokens, and cache_read_input_tokens.

    • cache_creation: BetaCacheCreation or null

      Breakdown of cached tokens by TTL

      • ephemeral_1h_input_tokens: number

        The number of input tokens used to create the 1 hour cache entry.

        default: 0, minimum: 0

      • ephemeral_5m_input_tokens: number

        The number of input tokens used to create the 5 minute cache entry.

        default: 0, minimum: 0

    • cache_creation_input_tokens: number or null

      The number of input tokens used to create the cache entry.

      minimum: 0

    • cache_read_input_tokens: number or null

      The number of input tokens read from the cache.

      minimum: 0

    • fallback_credit: BetaFallbackCreditUsage or null

      Outcome of the fallback_credit_token presented on this request.

      • status: BetaFallbackCreditRedeemed or BetaFallbackCreditNotApplied

        Whether the fallback-credit reprice was applied to this response's billing.

        A union discriminated on type. redeemed: the retry is billed as if the conversation had been on the retry model all along — including when the resulting shift is zero because there was nothing to move. not_applied: no reprice was applied; the arm's reason says why.

        • BetaFallbackCreditRedeemed object

          The reprice was applied: the retry is billed as if the conversation had been on the retry model all along.

          • type: "redeemed"

            default: redeemed

        • BetaFallbackCreditNotApplied object

          No reprice was applied; reason says why.

          • type: "not_applied"

            default: not_applied

          • reason: "body_mismatch" or "continuation_excluded" or "continuation_only" or 9 more

            Why the reprice was not applied.

            A closed enum; additions to the redemption-check vocabulary arrive as deliberate schema updates.

            • "body_mismatch"

            • "continuation_excluded"

            • "continuation_only"

            • "expired"

            • "invalid_target_model"

            • "not_enabled"

            • "reprice_unavailable"

            • "temporarily_unavailable"

            • "variant_fields_present"

            • "wrong_organization"

            • "wrong_platform"

            • "wrong_workspace"

          • remove_to_redeem: optional array of string or null

            Request fields to remove before retrying, so the retry can redeem this token.

            Present exactly when reason is variant_fields_present — never null, never an empty array; absent otherwise. Fields are named only from your own request, and only after the sealed variant hash matched. A served best-effort retry has already been billed at normal price; nothing redeems retroactively, but a corrected re-send inside the token's five-minute window can still redeem.

    • inference_geo: string or null

      The geographic region where inference was performed for this request.

    • input_tokens: number

      The number of input tokens which were used.

      minimum: 0

    • iterations: BetaIterationsUsage or null

      Per-iteration token usage breakdown.

      Each entry represents one sampling iteration, with its own input/output token counts and cache statistics, discriminated by type. For message entries (model sampling iterations, such as the turns of a server-side tool use loop), this allows you to:

      • Determine which iterations exceeded long context thresholds (>=200k tokens)
      • Calculate the context window size from the last message entry
      • Understand token accumulation across server-side tool use loops

      A compaction entry reports the token usage of the compaction operation itself — the server-side request that summarizes the context being closed — NOT the size of the context that was compacted away, and its token counts can be much smaller than that closed context (for example, a compaction that closes a ~200k-token context can report only a few thousand tokens). Do not derive the context window size from a compaction entry, even when it is the last entry. A compaction entry's tokens are not included in the top-level usage fields. When an input-token trigger is in effect (the default — 150,000 tokens unless configured otherwise), each compaction entry closes a context that had reached at least that threshold, though the context can exceed it by the final iteration's output and tool results.

      • BetaMessageIterationUsage object

        Token usage for a sampling iteration.

        • type: "message"

          Usage for a sampling iteration

          default: message

        • cache_creation: BetaCacheCreation or null

          Breakdown of cached tokens by TTL

        • cache_creation_input_tokens: number

          The number of input tokens used to create the cache entry.

          default: 0, minimum: 0

        • cache_read_input_tokens: number

          The number of input tokens read from the cache.

          default: 0, minimum: 0

        • input_tokens: number

          The number of input tokens which were used.

          minimum: 0

        • model: Model or null

          The model that will complete your prompt.

          See models for additional details and options.

        • output_tokens: number

          The number of output tokens which were used.

          minimum: 0

      • BetaCompactionIterationUsage object

        Token usage for a compaction iteration.

        • type: "compaction"

          Usage for a compaction iteration

          default: compaction

        • cache_creation: BetaCacheCreation or null

          Breakdown of cached tokens by TTL

        • cache_creation_input_tokens: number

          The number of input tokens used to create the cache entry.

          default: 0, minimum: 0

        • cache_read_input_tokens: number

          The number of input tokens read from the cache.

          default: 0, minimum: 0

        • input_tokens: number

          The number of input tokens which were used.

          minimum: 0

        • output_tokens: number

          The number of output tokens which were used.

          minimum: 0

      • BetaAdvisorMessageIterationUsage object

        Token usage for an advisor sub-inference iteration.

        • type: "advisor_message"

          Usage for an advisor sub-inference iteration

          default: advisor_message

        • cache_creation: BetaCacheCreation or null

          Breakdown of cached tokens by TTL

        • cache_creation_input_tokens: number

          The number of input tokens used to create the cache entry.

          default: 0, minimum: 0

        • cache_read_input_tokens: number

          The number of input tokens read from the cache.

          default: 0, minimum: 0

        • input_tokens: number

          The number of input tokens which were used.

          minimum: 0

        • model: Model

          The model that will complete your prompt.

          See models for additional details and options.

        • output_tokens: number

          The number of output tokens which were used.

          minimum: 0

      • BetaFallbackMessageIterationUsage object

        Token usage for the fallback-model attempt of a server-side fallback request.

        The terminal entry of a fallback-served turn: when a fallback hop's output is the returned message, the entry for the iteration that completed it carries this type in place of message. A declined hop and the serving hop's earlier tool-loop iterations produce message entries. Whether a fallback model served the response is signalled by the presence of this entry in usage.iterations.

        • type: "fallback_message"

          Usage for the fallback-model attempt that served the response

          default: fallback_message

        • cache_creation: BetaCacheCreation or null

          Breakdown of cached tokens by TTL

        • cache_creation_input_tokens: number

          The number of input tokens used to create the cache entry.

          default: 0, minimum: 0

        • cache_read_input_tokens: number

          The number of input tokens read from the cache.

          default: 0, minimum: 0

        • input_tokens: number

          The number of input tokens which were used.

          minimum: 0

        • model: Model

          The model that will complete your prompt.

          See models for additional details and options.

        • output_tokens: number

          The number of output tokens which were used.

          minimum: 0

    • output_tokens: number

      The number of output tokens which were used.

      minimum: 0

    • output_tokens_details: BetaOutputTokensDetails or null

      Breakdown of output tokens by category.

      output_tokens remains the inclusive, authoritative total used for billing. This object provides a read-only decomposition for observability — for example, how many of the billed output tokens were spent on internal reasoning that may have been summarized before being returned to you.

      • thinking_tokens: number

        Number of output tokens the model generated as internal reasoning, including the thinking-block delimiter tokens.

        Reflects the raw reasoning the model produced, not the (possibly shorter) summarized thinking text returned in the response body. Computed by re-tokenizing the raw reasoning text, so it may differ from the model's exact generation count by a small number of tokens. Always ≤ output_tokens; output_tokens - thinking_tokens approximates the non-reasoning output.

        default: 0, minimum: 0

    • server_tool_use: BetaServerToolUsage or null

      The number of server tool requests.

      • web_fetch_requests: number

        The number of web fetch tool requests.

        default: 0, minimum: 0

      • web_search_requests: number

        The number of web search tool requests.

        default: 0, minimum: 0

    • service_tier: "standard" or "priority" or "batch" or null

      If the request used the priority, standard, or batch tier.

      • "standard"

      • "priority"

      • "batch"

    • speed: "standard" or "fast" or null

      Inference speed mode. fast provides significantly faster output token generation at premium pricing. Not all models support fast; invalid combinations are rejected at create time.

      • "standard"

      • "fast"

  • input_transformations: optional array of BetaInputTransformation or null

    Changes the API made to the request's input before showing it to the model, and blocks that failed a binding check but were left unchanged: one entry per block, in request order. Two entry types today. thinking_dropped — a thinking, redacted_thinking or connector_text block from the request's messages that was removed from the prompt instead of being shown to the model because it failed a binding check. thinking_mismatch_allowed — a thinking or redacted_thinking block that failed the conversation check (the conversation before it differs from the one it was created in, or it carries no record of one on a model that requires it) and was shown to the model all the same, because that check is not enforced for this request. More entry types may be added over time; ignore types you do not recognize.

    Requires anthropic-beta: thinking-binding-controls-2026-08-01. Present on every such response from a model that supports extended thinking, as [] when there is no entry to report; without the beta, blocks are removed or left in place all the same but nothing is reported. Removed blocks contribute nothing to usage.input_tokens; blocks left in place count as sent. When streaming, the array is final in message_start; the final message_delta event carries it only when a server-side model fallback happened mid-stream, in which case it holds the serving model's entries and replaces the one in message_start.

    • BetaThinkingDroppedInputTransformation object

      • type: "thinking_dropped"

        Always thinking_dropped for this entry type.

        default: thinking_dropped

      • path: string

        Where the removed block was in your request, as messages.{i}.content.{j}: i indexes the messages array you sent and j that message's content array — the same form error messages use.

      • reason: "model_binding_mismatch" or "prefix_binding_mismatch" or "organization_binding_mismatch" or "end_user_binding_mismatch"

        Which binding check removed the block: model_binding_mismatch — it was created by a model whose reasoning the requested model may not read; prefix_binding_mismatch — the conversation before it differs from the conversation it was created in (the rest of that turn's consecutive thinking blocks are removed with it, each with this reason); organization_binding_mismatch — it was created under a different organization (an Anthropic organization, AWS account or Google Cloud project) and this organization is not one of its additional organizations; end_user_binding_mismatch — it was created for a different end user, or was removed by the consumer-organization binding. A block that would fail several checks reports one reason, in this order of precedence: organization_binding_mismatch, end_user_binding_mismatch, model_binding_mismatch, prefix_binding_mismatch.

        • "model_binding_mismatch"

        • "prefix_binding_mismatch"

        • "organization_binding_mismatch"

        • "end_user_binding_mismatch"

    • BetaThinkingMismatchAllowedInputTransformation object

      • type: "thinking_mismatch_allowed"

        Always thinking_mismatch_allowed for this entry type.

        default: thinking_mismatch_allowed

      • path: string

        Where the block is in your request, as messages.{i}.content.{j}: i indexes the messages array you sent and j that message's content array — the same form error messages use.

      • reason: "model_binding_mismatch" or "prefix_binding_mismatch" or "organization_binding_mismatch" or "end_user_binding_mismatch"

        Which binding check the block failed; the block was shown to the model all the same. Always prefix_binding_mismatch today — the conversation before the block differs from the conversation it was created in, or the block carries no record of one on a model that requires it. Were the check enforced for this request, the block would have been removed or the request rejected (thinking.block_binding.prefix_mismatch_behavior). A removal also takes the rest of that turn's consecutive thinking blocks, whereas here each block is checked on its own, so thinking_mismatch_allowed entries are a lower bound on what enforcement would remove.

        • "model_binding_mismatch"

        • "prefix_binding_mismatch"

        • "organization_binding_mismatch"

        • "end_user_binding_mismatch"

• BetaRawMessageStreamEvent = BetaRawMessageStartEvent or BetaRawMessageDeltaEvent or BetaRawMessageStopEvent or 3 more

  • BetaRawMessageStartEvent object

    • type: "message_start"

      default: message_start

    • message: BetaMessage

  • BetaRawMessageDeltaEvent object

    • type: "message_delta"

      default: message_delta

    • context_management: BetaContextManagementResponse or null

      Information about context management strategies applied during the request

    • delta: object

      • container: BetaContainer or null

        Information about the container used in the request (for the code execution tool)

      • stop_details: BetaRefusalStopDetails or null

        Structured information about a refusal.

      • stop_reason: BetaStopReason or null

      • stop_sequence: string or null

    • usage: BetaMessageDeltaUsage

      Billing and rate-limit usage.

      Anthropic's API bills and rate-limits by token counts, as tokens represent the underlying cost to our systems.

      Under the hood, the API transforms requests into a format suitable for the model. The model's output then goes through a parsing stage before becoming an API response. As a result, the token counts in usage will not match one-to-one with the exact visible content of an API request or response.

      For example, output_tokens will be non-zero, even for an empty string response from Claude.

      Total input tokens in a request is the summation of input_tokens, cache_creation_input_tokens, and cache_read_input_tokens.

      • cache_creation_input_tokens: number or null

        The cumulative number of input tokens used to create the cache entry.

        minimum: 0

      • cache_read_input_tokens: number or null

        The cumulative number of input tokens read from the cache.

        minimum: 0

      • fallback_credit: BetaFallbackCreditUsage or null

        Outcome of the fallback_credit_token presented on this request.

      • input_tokens: number or null

        The cumulative number of input tokens which were used.

        minimum: 0

      • iterations: BetaIterationsUsage or null

        Per-iteration token usage breakdown.

        Each entry represents one sampling iteration, with its own input/output token counts and cache statistics, discriminated by type. For message entries (model sampling iterations, such as the turns of a server-side tool use loop), this allows you to:

        • Determine which iterations exceeded long context thresholds (>=200k tokens)
        • Calculate the context window size from the last message entry
        • Understand token accumulation across server-side tool use loops

        A compaction entry reports the token usage of the compaction operation itself — the server-side request that summarizes the context being closed — NOT the size of the context that was compacted away, and its token counts can be much smaller than that closed context (for example, a compaction that closes a ~200k-token context can report only a few thousand tokens). Do not derive the context window size from a compaction entry, even when it is the last entry. A compaction entry's tokens are not included in the top-level usage fields. When an input-token trigger is in effect (the default — 150,000 tokens unless configured otherwise), each compaction entry closes a context that had reached at least that threshold, though the context can exceed it by the final iteration's output and tool results.

      • output_tokens: number

        The cumulative number of output tokens which were used.

      • output_tokens_details: BetaOutputTokensDetails or null

        Breakdown of output tokens by category.

        output_tokens remains the inclusive, authoritative total used for billing. This object provides a read-only decomposition for observability — for example, how many of the billed output tokens were spent on internal reasoning that may have been summarized before being returned to you.

      • server_tool_use: BetaServerToolUsage or null

        The number of server tool requests.

    • input_transformations: optional array of BetaInputTransformation or null

      Changes the API made to the request's input before showing it to the model, and blocks that failed a binding check but were left unchanged: one entry per block, in request order. Two entry types today. thinking_dropped — a thinking, redacted_thinking or connector_text block from the request's messages that was removed from the prompt instead of being shown to the model because it failed a binding check. thinking_mismatch_allowed — a thinking or redacted_thinking block that failed the conversation check (the conversation before it differs from the one it was created in, or it carries no record of one on a model that requires it) and was shown to the model all the same, because that check is not enforced for this request. More entry types may be added over time; ignore types you do not recognize.

      Requires anthropic-beta: thinking-binding-controls-2026-08-01. Present on every such response from a model that supports extended thinking, as [] when there is no entry to report; without the beta, blocks are removed or left in place all the same but nothing is reported. Removed blocks contribute nothing to usage.input_tokens; blocks left in place count as sent. When streaming, the array is final in message_start; the final message_delta event carries it only when a server-side model fallback happened mid-stream, in which case it holds the serving model's entries and replaces the one in message_start.

      • BetaThinkingDroppedInputTransformation object

      • BetaThinkingMismatchAllowedInputTransformation object

  • BetaRawMessageStopEvent object

    • type: "message_stop"

      default: message_stop

  • BetaRawContentBlockStartEvent object

    • type: "content_block_start"

      default: content_block_start

    • content_block: BetaTextBlock or BetaThinkingBlock or BetaRedactedThinkingBlock or 14 more

      • BetaTextBlock object

      • BetaThinkingBlock object

      • BetaRedactedThinkingBlock object

      • BetaToolUseBlock object

      • BetaServerToolUseBlock object

      • BetaWebSearchToolResultBlock object

      • BetaWebFetchToolResultBlock object

      • BetaAdvisorToolResultBlock object

      • BetaCodeExecutionToolResultBlock object

      • BetaBashCodeExecutionToolResultBlock object

      • BetaTextEditorCodeExecutionToolResultBlock object

      • BetaToolSearchToolResultBlock object

      • BetaMCPToolUseBlock object

      • BetaMCPToolResultBlock object

      • BetaContainerUploadBlock object

        Response model for a file uploaded to the container.

      • BetaCompactionBlock object

        A compaction block returned when autocompact is triggered.

        When content is None, it indicates the compaction failed to produce a valid summary (e.g., malformed output from the model). Clients may round-trip compaction blocks with null content; the server treats them as no-ops.

      • BetaFallbackBlock object

        Marks the point in content where one model's output gives way to the next.

        One block appears per hop where a preceding model actually ran this turn and declined. A turn where no preceding model ran and declined has no such boundary and carries no block — the signal for whether a fallback model served the response is the presence of a fallback_message entry in usage.iterations, not this block.

        The block is treated like a server-tool content block for streaming: it arrives via the standard content_block_start / content_block_stop pair and carries no deltas.

    • index: number

  • BetaRawContentBlockDeltaEvent object

    • type: "content_block_delta"

      default: content_block_delta

    • delta: BetaRawContentBlockDelta

      • BetaTextDelta object

        • type: "text_delta"

          default: text_delta

        • text: string

      • BetaInputJSONDelta object

        • type: "input_json_delta"

          default: input_json_delta

        • partial_json: string

      • BetaCitationsDelta object

        • type: "citations_delta"

          default: citations_delta

        • citation: BetaCitationCharLocation or BetaCitationPageLocation or BetaCitationContentBlockLocation or 2 more

          • BetaCitationCharLocation object

          • BetaCitationPageLocation object

          • BetaCitationContentBlockLocation object

          • BetaCitationsWebSearchResultLocation object

          • BetaCitationSearchResultLocation object

      • BetaThinkingDelta object

        • type: "thinking_delta"

          default: thinking_delta

        • estimated_tokens: number or null

          Per-frame increment of a coarse, running estimate of the tokens this thinking block has produced so far. Present whenever the thinking-token-count-2026-05-13 beta is set; null unless thinking.display resolves to "omitted" and a count is due this frame. Sum the increments across thinking_delta frames on this block for a progress indicator. Each increment is a non-negative multiple of a fixed quantum and the cadence is rate-limited, so this is a deliberately lossy display hint, not a billable count; usage.output_tokens remains authoritative.

        • thinking: string

          The incremental thinking text for this content block. Concatenate the thinking values of successive thinking_delta events to assemble the block's full thinking value.

      • BetaSignatureDelta object

        • type: "signature_delta"

          default: signature_delta

        • signature: string

          The signature for this thinking block: an opaque value used to verify that the block was generated by Claude when it is passed back to the API. Delivered in a signature_delta event just before the block's content_block_stop event.

      • BetaCompactionContentBlockDelta object

        • type: "compaction_delta"

          default: compaction_delta

        • content: string or null

        • encrypted_content: string or null

          Opaque metadata from prior compaction, to be round-tripped verbatim

    • index: number

  • BetaRawContentBlockStopEvent object

    • type: "content_block_stop"

      default: content_block_stop

    • index: number

# Example

curl https://api.anthropic.com/v1/messages \
    -H 'Content-Type: application/json' \
    -H 'anthropic-version: 2023-06-01' \
    -H "X-Api-Key: $ANTHROPIC_API_KEY" \
    --max-time 600 \
    -d '{
          "max_tokens": 1024,
          "messages": [
            {
              "content": "Hello, world",
              "role": "user"
            }
          ],
          "model": "claude-opus-5",
          "stream": false,
          "system": [
            {
              "text": "Today'\''s date is 2024-06-01.",
              "type": "text"
            }
          ],
          "temperature": 1,
          "thinking": {
            "type": "adaptive"
          },
          "tools": [
            {
              "input_schema": {
                "type": "object",
                "properties": {
                  "location": "bar",
                  "unit": "bar"
                },
                "required": [
                  "location"
                ]
              },
              "name": "name"
            }
          ],
          "top_k": 5,
          "top_p": 0.7
        }'