Messages auto (Anthropic-compatible)

Anthropic Messages API over x402 - point the Anthropic SDK (or Claude Code / the Agent SDK) at base_url https://agent402.tools/v1/auto and pay $0.01 per call in USDC, no API key, no signup. Same models, caps and price as this tier's /chat/completions route; any model here is served through the Messages wire (Claude natively, others translated). Up to 16,000 input chars and 1024 output tokens; streaming supported. Omit "model" and the gateway routes the prompt to the top-ranked model for its task type; the response adds agent402_router {category, quality, served}.

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Input

Example output

{
  "id": "msg_…",
  "type": "message",
  "role": "assistant",
  "model": "anthropic/claude-sonnet-5",
  "content": [
    {
      "type": "text",
      "text": "x402 is an HTTP-native way for agents to pay per request with USDC."
    }
  ],
  "stop_reason": "end_turn",
  "usage": {
    "input_tokens": 14,
    "output_tokens": 18
  }
}

Try it - see the 402 challenge (free)

curl -i -X POST https://agent402.tools/v1/auto/messages \
  -H "Content-Type: application/json" \
  -d '{"max_tokens":256,"messages":[{"role":"user","content":"Summarize x402 in one sentence."}]}'

The response is HTTP 402 Payment Required with exact payment requirements. Any x402 v2 client pays automatically and retries:

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/v1/auto/messages", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "max_tokens": 256,
    "messages": [
      {
        "role": "user",
        "content": "Summarize x402 in one sentence."
      }
    ]
  }),
});

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