Explainer
What is x402?
An open protocol that uses HTTP 402 so a client can pay a server, usually in USDC, and retry.
x402 is a payment protocol introduced publicly by Coinbase on 6 May 2025. A server that wants to charge for a resource responds with HTTP 402 and machine-readable payment requirements. A client that can pay attaches proof and repeats the request.
The protocol is named for the reserved HTTP status “Payment Required.” x402 does not invent a new status code. It specifies what a 402 means to a machine, typically via headers, and how settlement is verified through a facilitator.
Foundry’s first production rail uses exact USDC payments on Base mainnet through the authenticated Coinbase CDP facilitator. That is a policy choice. The protocol documentation also lists other networks and facilitators.