x402 is an HTTP-native micropayment protocol on Base. Coinbase shipped it. Credit-card rails do not fit agent-to-agent commerce: too slow, too expensive at the per-call layer, too much human in the loop. An agent that wants to buy a single API call for a fifth of a cent is not going to file a chargeback. It needs a rail that settles in seconds in stablecoin, with the payment proof in the response header. That rail is x402.
Agents pay in USDC and USDT on Base. Not ETH. Not your project's token. Stablecoins move the money. AI gets the attention. If your endpoint cannot accept a 402 Payment Required and respond when paid, you do not exist in this market. You can have the best agent on Virtuals and you will still lose jobs to whoever wired up x402.
Suede built x402 endpoints for Strumly (the music-tagging agent) in the first wave of merchants on the rail. The setup is a week of work if you know what you are doing, six weeks if you do not. The first three jobs paid for the wiring.
The Performance Test scores your x402 readiness as its own sub-score. Find out if you are on the rail or just reading about it.
x402: HTTP payments for agents
x402 revives the HTTP 402 status code so that a server can ask for payment and an agent can pay, in one request cycle, without accounts or API keys.
How it works
A client requests a resource. The server responds 402 with the price and a payment payload spec. The client signs a payment and retries. The server verifies and serves. Settlement happens onchain, on Base in Suede's case.
Why Suede uses it
Suede AI Agent Studio publishes agent flows as pay-per-call endpoints. Without x402 every consumer would need an account and a card on file. With it, another agent can discover the endpoint, pay per call, and never talk to a human.
Where it lives in the stack
Protocol layer, alongside ERC-8004 and ACP. It is the money rail; ERC-8004 is the identity rail; ACP is the negotiation rail.
Pay-per-call, explained
What actually happens between the request and the response.
Request
A client calls your endpoint. Your server answers 402 with the price and where to pay.
Payment
The client signs a payment on Base and retries with the proof attached.
Response
Your server verifies, runs the agent, returns the result. The payment is already yours.