# Streaming — four SSE dialects and five WebSocket families

Status: event names and statuses from generated/streaming-events.json (506 records: OpenAI 282, Anthropic 68, xAI 94, Gemini 62); observed sequences quoted from docs/openai/streaming-events.md, docs/anthropic/streaming.md, docs/xai/streaming.md, docs/gemini/streaming.md, docs/gemini/interactions-api.md, docs/gemini/live-events.md (LIVE_VERIFIED 2026-09-18/19 on gpt-5.4-nano, claude-haiku-4-5-20251001, grok-4.3, gemini-3.5-flash-lite / gemini-3.8-flash). Sources: https://developers.openai.com/api/docs/guides/streaming-responses · https://developers.openai.com/api/reference/resources/responses/streaming-events · https://platform.claude.com/docs/en/build-with-claude/streaming · https://docs.x.ai/developers/model-capabilities/text/streaming · https://docs.x.ai/developers/model-capabilities/audio/speech-to-speech · https://ai.google.dev/api/generate-content#method:-models.streamgeneratecontent · https://ai.google.dev/gemini-api/docs/live · https://ai.google.dev/gemini-api/docs/interactions Last verified: 2026-09-18

# 1. Wire format

# 2. Skeletons (observed live)

OpenAI Responses — "Reply with OK."

response.created(0) → response.in_progress(1) → response.output_item.added(2, message) → response.content_part.added(3)
→ response.output_text.delta(4 "OK") → response.output_text.done(5) → response.content_part.done(6) → response.output_item.done(7) → response.completed(8)

Anthropic Messages

message_start → content_block_start(0, text) → ping → content_block_delta(text_delta "OK") → content_block_delta(".") → content_block_stop(0)
→ message_delta(stop_reason end_turn, usage) → message_stop

xAI Responses (grok-4.3) — reasoning item first

response.created → response.in_progress → response.output_item.added(reasoning) → response.reasoning_summary_part.added → response.reasoning_summary_text.delta… → response.reasoning_summary_text.done
→ response.reasoning_summary_part.done → response.output_item.done → response.output_item.added(message) → response.content_part.added → response.output_text.delta("OK") → response.output_text.done
→ response.content_part.done → response.output_item.done → response.completed

xAI Chat Completions

data: {chunk delta.reasoning_content…} → data: {chunk delta.content "OK"} → data: {chunk finish_reason: stop} → [data: {choices: [], usage}] → data: [DONE]

xAI /v1/messages — message_start → content_block_start(thinking) → content_block_delta(thinking_delta)… → content_block_stop → content_block_start(text, index 0 again) → content_block_delta(text_delta) → content_block_stop → message_delta → message_stop (no ping; index reuse is a quirk).

Gemini streamGenerateContent?alt=sse (gemini-3.8-flash)

data: {candidates:[{content:{parts:[{text:"OK", thought?}]}}], usageMetadata, modelVersion, responseId}
data: {candidates:[{content:{parts:[{text:"", thoughtSignature:"…"}]}, finishReason:"STOP"}], usageMetadata:{…thoughtsTokenCount}}

With includeThoughts: true, {text, thought: true} parts stream first (not guaranteed on trivial prompts). JSON-mode deltas are partial JSON strings that concatenate.

Gemini Interactions (stream: true)

interaction.created → interaction.status_update → step.start(thought) → step.delta{thought_signature} → step.stop → step.start(model_output) → step.delta{text "OK"} → step.stop → interaction.completed → done [DONE]

# 3. Event-name mapping — the four text streams

Counts: OpenAI Responses SSE 63 + WebSocket 69/3, Chat 2; Anthropic Messages 13 core + 10 advanced; xAI Responses 24, Chat 3, Messages 6; Gemini generate-content 8 (framing + chunk kinds), Interactions 15. Full lists: FAQ Q4.

# 4. Usage and stop information

# 5. The same streamed call on all four providers

# OpenAI
curl -N https://api.openai.com/v1/responses -H "Authorization: Bearer $OPENAI_API_KEY" -H "Content-Type: application/json" \
  -d '{"model":"gpt-5.4-nano","input":"Reply with OK.","max_output_tokens":32,"stream":true}'
# Anthropic
curl -N https://api.anthropic.com/v1/messages -H "x-api-key: $ANTHROPIC_API_KEY" -H "anthropic-version: 2023-06-01" -H "content-type: application/json" \
  -d '{"model":"claude-haiku-4-5-20251001","max_tokens":32,"messages":[{"role":"user","content":"Reply with OK."}],"stream":true}'
# xAI (OpenAI event names; reasoning summary events come first)
curl -N https://api.x.ai/v1/responses -H "Authorization: Bearer $XAI_API_KEY" -H "Content-Type: application/json" \
  -d '{"model":"grok-4.3","input":"Reply with OK.","reasoning":{"effort":"low"},"max_output_tokens":64,"stream":true}'
# Gemini (SSE framing requires ?alt=sse; without it you get a JSON array)
curl -N "https://generativelanguage.googleapis.com/v1beta/models/gemini-3.5-flash-lite:streamGenerateContent?alt=sse" \
  -H "x-goog-api-key: $GEMINI_API_KEY" -H "Content-Type: application/json" \
  -d '{"contents":[{"role":"user","parts":[{"text":"Reply with OK."}]}],"generationConfig":{"maxOutputTokens":64,"thinkingConfig":{"thinkingLevel":"minimal"}}}'

Client algorithm that works for all four: dispatch on the event name where one exists (OpenAI/xAI event:, Anthropic event:, Interactions event:), otherwise on chunk shape (Gemini candidates[0].content.parts[]); accumulate text per (OpenAI/xAI output_index,content_index) / (Anthropic block index) / (Gemini part position); accumulate tool-argument fragments and parse at …arguments.done / content_block_stop / the complete functionCall part; take the final object from the terminal event (response.completed.response, interaction.completed) or rebuild it (message_start + deltas; last Gemini chunk + concatenated parts). SDK helpers: client.responses.stream().get_final_response() (OpenAI, and xAI via the OpenAI SDK), client.messages.stream().get_final_message() (Anthropic), client.chat.create(...).stream() (xai-sdk, gRPC), client.models.generate_content_stream() / client.interactions.create(stream=True) (google-genai).

# 6. Beyond SSE — WebSocket message families

# Realtime / Live message-family mapping

# 7. Streaming constraints and gotchas

Related: features · tool-execution · realtime-and-media · agents-platforms · docs/openai/streaming-events.md · docs/anthropic/streaming.md · docs/xai/streaming.md · docs/xai/voice.md · docs/gemini/streaming.md · docs/gemini/live-events.md.