x402 API

The x402 API is a speech-to-text API for AI agents. It transcribes audio and video files asynchronously and charges each job to the agent's wallet in USDC on Base, with no account or API key. Send the job request, get 402 Payment Required with the price, pay it with an x402 client, and then read the result for free or receive it by webhook. A job accepts the same options as a Jobs API job, except the progress stream.

Why x402

The x402 API enables an application or autonomous AI agent to pay for transcription per job directly from its own wallet, using native USDC on the Base network. Because payment occurs over standard HTTP 402 responses, you do not need to create a Speech is Cheap account, enter a credit card, commit to a monthly subscription, or store API keys in your environment. Pricing follows standard pay-as-you-go rates, and any unused purchased time or failed jobs are automatically refunded to the paying wallet. This makes x402 a good fit for autonomous agents with independent budgets, multi-tenant agent workflows, and ad-hoc scripts where ongoing account maintenance is undesirable.

An API key is the better choice when your workload benefits from centralized account management. High-volume users can lower per-minute costs by choosing the monthly subscription plan. API keys are also required if you want the Server-Sent Events progress stream (x402 supports only polling and webhooks) or need the synchronous Edge API for instant short-audio responses. Finally, API keys provide consolidated usage metrics and Stripe invoices through the Dashboard.

How It Works

1. Request a quote. POST your job to https://api.speechischeap.com/v2/x402/jobs/ without payment. The service answers 402 Payment Required with the price and the address to pay in a PAYMENT-REQUIRED header. A quote is free and valid for 300 seconds.
2. Pay. Your x402 client signs a USDC transfer authorization for the quoted amount. Send the same request again with the signed proof in a PAYMENT-SIGNATURE header.
3. Confirm. The service settles the payment on Base and answers 202 Accepted. Confirming the payment takes a few seconds, so the first answer usually reports payment_status: "stripe_pending" and has no job id. Send the same request and proof again until the answer has an id. A replay never charges you again.
4. Transcribe. A URL job starts as soon as the payment is confirmed. For an upload, the answer is READY with a one-use upload_token. Send the file with it to https://upload.speechischeap.com/v2/x402/jobs/ within 300 seconds.
5. Receive the result. Read it with a free GET request, or receive it at your webhook_url.

If a job fails, is canceled, or finishes shorter than you paid for, the service refunds the difference to your wallet. See Payments and Refunds.

Network and Asset

Setting	Value
Scheme	x402 v2 exact (EIP-3009 transferWithAuthorization)
Network	Base mainnet, eip155:8453
Asset	Native USDC, 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913
Amount	USDC atomic units with six decimals, so 10000 is $0.01

The service accepts no other network or token. Your wallet needs only USDC: the service submits the transfer and pays the network fee.

What You Need

• An x402 v2 client that supports the exact scheme on Base, such as @x402/fetch.
• A wallet with USDC on Base and a signer for EIP-712 typed data. Canceling a job also needs EIP-191 message signing.
• The duration of each file in seconds. The service doesn't measure a file before you pay. For example, ffprobe -v error -show_entries format=duration -of csv=p=0 audio-file.mp3 prints it.
• Optionally, an endpoint for webhooks.

You need no Speech is Cheap account, API key, or card.

Authentication

There's no API key. The payment authorizes a job, and the paying wallet's signature authorizes canceling it. Reading a job needs no authentication.

Endpoints

The API uses two hosts, https://api.speechischeap.com/v2/ and https://upload.speechischeap.com/v2/.

Method	URL	Page
POST	https://api.speechischeap.com/v2/x402/jobs/	Create a Job from a URL, or the first step of Upload a File with input_type set to upload
POST	https://upload.speechischeap.com/v2/x402/jobs/	Upload a File
GET	https://api.speechischeap.com/v2/jobs/:job_id	Get a Job
DELETE	https://api.speechischeap.com/v2/x402/jobs/:job_id	Cancel a Job

States

Before a Job Exists

A paid request that has no job id yet returns a purchase status:

Status	Meaning	What to do
PENDING	The payment isn't confirmed. payment_status says where it stands.	Send the same request and proof again.
UNCLAIMED	A URL purchase is paid and waiting to start.	Send the same request and proof again.
READY	An upload purchase is paid. The answer has upload_url and upload_token.	Send the file within 300 seconds.
CLAIMED	An upload is in progress.	Wait for the upload to finish.
EXPIRED	A paid purchase wasn't used in time, for example an upload that didn't start within 300 seconds. The service refunds it in full.	Start a new purchase.
FAILED	The purchase failed before a job was created, for example because the file URL was unreachable or an upload failed. The service refunds it in full.	Fix the cause and start a new purchase.

While the status is PENDING, payment_status is one of these:

Payment status	Meaning
quoted	The service hasn't finished verifying the proof. Another request may be verifying it now.
settling	The service is submitting the transfer on Base.
settlement_unknown	The service doesn't yet know whether the transfer succeeded. It keeps checking Base.
stripe_pending	The transfer succeeded and the service is confirming the payment.

Job States

Once the answer has an id, the job's status is PENDING, COMPLETED, FAILED, or CANCELED, as in the Jobs API. Get a Job explains each one.

Receiving Results

• Poll. Get a Job is free and needs no payment, signature, or key.
• Webhook. Set webhook_url and the service sends the job's outcome and any refund updates to it. It retries failed deliveries for up to 24 hours. See Webhooks.

The job's GET response is the source of truth for its result.

Runnable Example

x402-client.mjs pays for a job with @x402/fetch, saves its proof before it pays, and replays a pending payment. Setup and usage are in Create a Job from a URL.

Related Pages

• Input Requirements lists the duration, size, and URL rules.
• Supported File Types lists the accepted containers and codecs.
• Supported Languages lists the language codes.
• Output and Add-ons describes the result and its optional fields.
• Errors lists every error message and how to recover.