How x402 works
The web had a status code for payments. Now it works.
x402 lets an AI agent pay for a single API call the moment it needs it, in dollars, without an account, a subscription or an invoice. Here is one call, step by step. Click any step.
AI agent
The agent asks
An AI agent calls your API, just like any app would.
No account, no API key, no sign-up. The request is an ordinary HTTPS call.
AI agent
x402Fi gateway
Robinhood Chain
GET /g/fx-rates?pair=EURUSD
Why it matters to a business
- New customers. Agents can buy from you without a human signing up first.
- No billing stack. No keys to issue, no invoices to chase, no card fees on tiny amounts.
- Prices that fit. Charge a cent per call if that is what a call is worth.
- Instant settlement. Money arrives with the request, every day of the year.
What it does not do
- It does not identify the buyer. A payment proves a wallet paid, not who owns it.
- It does not replace contracts or terms of service for large customers.
- It cannot reverse a settled payment. Disputes are handled between buyer and seller.
- It is not a security of any kind and pays no yield. It is a payment.
Glossary
- x402
- An open standard for paying for things over HTTP. It gives the long-reserved status code 402 (Payment Required) a precise meaning, so software can pay software without accounts or API keys.
- HTTP 402
- The reply that says “this costs money” and includes the exact price, token, network and recipient.
- USDG
- Global Dollar, a US-dollar stablecoin issued by Paxos. One USDG is designed to be redeemable for one dollar.
- Robinhood Chain
- A public blockchain (network ID 4663) where the USDG transfer is recorded. Payments are final within seconds.
- Facilitator
- The service that checks a payment signature and submits it to the chain. x402Fi runs one for Robinhood Chain and pays the network fee.
- payTo
- The wallet that receives the money. In a 402 quote it is chosen by the seller.
- Verified payee
- A check, defined by the x402 payee-name extension, that the service's address and its payTo wallet are both listed on an ENS name. Only the name's owner can write those records, so a passing check means the same party controls both.
- EIP-3009 authorization
- A signed permission to move an exact amount once, before a deadline. The buyer signs; anyone can submit it; nobody can change the amount or reuse it.
- Pay only for answers
- On x402Fi the payment is settled after the seller's API responds successfully. If the API errors or times out, the authorization is never used and the buyer is not charged.