Responses nano (OpenAI Responses API)

OpenAI Responses API over x402 - point the OpenAI SDK's responses.create() (or the OpenAI Agents SDK) at base_url https://agent402.tools/v1/nano and pay $0.003 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 Responses wire. Up to 12,000 input chars and 768 output tokens; streaming supported; function tools yes, server-side tools (web_search, file_search, computer, mcp) no; no stored conversation state (send the full input each call).

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Input

Example output

{
  "id": "resp_…",
  "object": "response",
  "status": "completed",
  "model": "openai/gpt-4o-mini",
  "output": [
    {
      "id": "msg_…",
      "type": "message",
      "role": "assistant",
      "status": "completed",
      "content": [
        {
          "type": "output_text",
          "text": "x402 is an HTTP-native way for agents to pay per request with USDC.",
          "annotations": []
        }
      ]
    }
  ],
  "usage": {
    "input_tokens": 14,
    "output_tokens": 18,
    "total_tokens": 32
  }
}

Try it - see the 402 challenge (free)

curl -i -X POST https://agent402.tools/v1/nano/responses \
  -H "Content-Type: application/json" \
  -d '{"model":"openai/gpt-4.1-nano","input":"Summarize x402 in one sentence.","max_output_tokens":128}'

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/nano/responses", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "model": "openai/gpt-4.1-nano",
    "input": "Summarize x402 in one sentence.",
    "max_output_tokens": 128
  }),
});

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