x402

x402 is an open payment standard that revives the long-dormant HTTP 402 "Payment Required" status code to add native payments to ordinary HTTP requests. When a client requests a resource that costs money, the server responds with a 402 status and payment instructions; the client attaches proof of a stablecoin payment and retries the request, and the server verifies the payment before returning the data. The whole exchange happens within a single HTTP round trip, without user accounts, API keys, credit cards, or subscription sign-ups. The protocol was introduced by Coinbase and is now stewarded under Linux Foundation governance as a neutral, chain-agnostic standard, with the x402 Foundation coordinating its development. It settles payments in stablecoins such as USDC and works across EVM-compatible chains and Solana. Integration is designed to be minimal on the server side, effectively adding one line of code to require payment on an endpoint before a request is fulfilled. The design principles emphasize no protocol fees beyond normal network costs, fast settlement, no required personal information, and an open, permissionless structure that any server or client can implement. x402 is aimed at developers who want to monetize APIs or digital content in a way that AI agents and automated software can pay for programmatically, without the friction of human checkout flows. By the tool's own reporting, it has processed tens of millions of transactions and tens of millions of dollars in volume since launch. As a machine-to-machine payment standard rather than a consumer product, it is not something end users interact with directly.