Speech-to-text, long audio (OpenAI transcription wire)

OpenAI's transcription wire on the ten-minute tier: POST multipart/form-data with a `file` part. Send POST /v1/pro/audio/transcriptions with the required field file and pay $0.100 per call over x402 or MPP (there is no free tier). It returns a JSON object with text, duration and model.

Same model as /v1/audio/transcriptions with a longer cap, for a recording a four-minute route refuses.

Category: AI & compute · Tags: stt speech-to-text transcription audio whisper openai

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Parameters

Example request

curl -i -X POST https://agent402.tools/v1/pro/audio/transcriptions \
  -H "Content-Type: application/json" \
  -d '{"file":"<audio bytes, multipart part named file>"}'

Without payment this returns HTTP 402 Payment Required with the exact price for v1-audio-transcriptions-pro; any x402 v2 or MPP client pays it and retries.

Example response

{
  "text": "Example transcript.",
  "duration": 420.5,
  "model": "gpt-transcribe"
}

From an MCP client

catalog.call {
  "slug": "v1-audio-transcriptions-pro",
  "params": {
    "file": "<audio bytes, multipart part named file>"
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for v1-audio-transcriptions-pro; the stdio package pays it from a wallet or from AGENT402_CREDITS_KEY. Local install: npx -y agent402-mcp.

Errors and behavior

• file is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Wallet-only: this tool runs a model, so it has no proof-of-work tier. A prepaid card-credits key issued earlier (Authorization: Bearer a402_...) also pays it.
• Model-backed: the answer is generated by a model, so the same input can produce different wording.
• A GET or HEAD to /v1/pro/audio/transcriptions returns the same 402 quote, so the price can be read without a body.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB and a streamed response are not replayed).

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();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/v1/pro/audio/transcriptions", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "file": "<audio bytes, multipart part named file>"
  }),
});

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