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1// System prompt as text blocks with cache_control2// STATUS: LIVE_VERIFIED 2026-09-18 with @anthropic-ai/sdk 0.126.0.3// Run: node --env-file=.env --experimental-strip-types examples/anthropic/messages/system.ts (ANTHROPIC_API_KEY read from env by the SDK)4import Anthropic from "@anthropic-ai/sdk";5import { appendFileSync } from "node:fs";67const client = new Anthropic();8const MODEL = "claude-haiku-4-5-20251001";9const log = (path: string, status: number, note: string) =>10 appendFileSync("reports/live-requests.jsonl", JSON.stringify({ ts: new Date().toISOString().replace(/\.\d+Z$/, "Z"), provider: "anthropic", method: "POST", path, status, est_cost_usd: 0.00005, note }) + "\n");11const msg = await client.messages.create({12 model: MODEL, max_tokens: 16,13 system: [{ type: "text", text: "You are terse. Answer in one word.", cache_control: { type: "ephemeral" } }],14 messages: [{ role: "user", content: "Reply with OK." }],15});16console.log(msg.content[0]?.type === "text" ? msg.content[0].text : "", "| cache_creation:", JSON.stringify(msg.usage.cache_creation));17log("/v1/messages", 200, "example system.ts");18