Track 2 · What you can do6 of 6
Paid API requests (x402)
A server can answer a request with “Payment Required,” and a client (including an AI agent) pays in tokens on-chain and gets its answer back in the same exchange. No account, no API key, no card.
The web has always had a status code for this (“402 Payment Required”), reserved decades ago and almost never used. XChain makes it real. A server can ask to be paid in tokens, and the client can pay on-chain and receive its answer in a single back-and-forth, with nothing to sign up for.
Built on a standard web status code
There's nothing exotic to install. x402 is a convention layered on ordinary web requests and ordinary token transfers: the server answers with a “402” challenge that names the price, the address to pay, and a one-time invoice; the client pays and comes back with the transaction as proof. Each invoice is single-use, so a payment can't be replayed or front-run.
Three ways to pay
A server can accept payment per request (send tokens for each call), as a membership (hold a particular token and you're in), or from a prepaid balance you top up once and draw down as you go. The server lists which methods it accepts, and the client picks one.
Made for AI agents
An autonomous agent can hit a paid endpoint, read the challenge, pay from a bounded wallet, and carry on, with no human signing up for an account or pasting in an API key. Machine-to-machine payment becomes part of the request itself.
Verified against the chain, not a middleman
Payment is proven by a transaction the server checks directly against the blockchain: the live mempool for instant, low-value access, or a confirmed block for anything irreversible. There's no payment processor and no trusted relay sitting in between.
An honest set of limits
x402 adds no new on-chain action and needs no consensus change; it rides on top of what's already there. Prices are quoted in token amounts (dollar quoting rides on the platform's price oracle). Instant, unconfirmed access is provisional and can still fail to confirm, so servers re-check it. And like any agent payment, it protects the request, not the wallet key behind it.
What you can build
Pay-per-call APIs and data feeds, metered access to a model or service, token-holder-only endpoints, and paid tools an AI agent can reach and pay for entirely on its own.