x402
An open payment standard that revives HTTP 402 Payment Required so an API can quote a price in its response and a client can pay it inline, per request.
x402 is an open payment protocol that turns the long-dormant HTTP status code 402 ("Payment Required") into a working payment handshake. When a client calls a protected endpoint without payment, the server responds with 402 and a machine-readable challenge describing how much to pay and on which rail. The client signs and submits the payment, then retries the request with proof of payment attached, and the server returns the response. The whole exchange happens inside ordinary HTTP, so any agent that can make a request can also pay for it.
The standard was introduced by Coinbase for EVM chains, where each call settles point-to-point on-chain. Proxygate supports x402 as one of its settlement rails. Agents can top up a prepaid Proxygate balance over x402: a GET to the top-up endpoint returns a 402 challenge carrying a ready-to-sign Solana deposit transaction, which the agent signs, submits, and confirms. From then on, calls are metered against that prepaid balance rather than settled one transaction at a time.
x402 matters for agentic commerce because it removes the human steps from payment. There is no checkout page, no API-key provisioning flow, and no subscription to negotiate. An autonomous agent discovers a price at request time and decides whether to pay, which is the behavior a marketplace of machine buyers needs. Proxygate treats x402 as a supported rail rather than a competitor: the marketplace, key injection, and netting sit above the payment layer, and x402 is one of several ways value moves.
Related concepts
x402: frequently asked questions
x402 is an open standard that uses the HTTP 402 Payment Required status code to let a server quote a price and a client pay it inline, per request. The server returns a 402 challenge, the client signs and submits payment, and then retries the call with proof of payment.
Proxygate supports x402 as a settlement rail. An agent can top up its prepaid USDC balance over x402: the top-up endpoint returns a 402 challenge with a ready-to-sign Solana deposit transaction. After funding, calls are metered against the prepaid balance.
x402 is a mechanism for paying per call, but they are not identical. Native x402 settles each call point-to-point. Proxygate can also net many metered calls against a single prepaid balance funded over x402, which avoids an on-chain transaction for every request.
x402 was introduced for EVM chains by Coinbase and has since been adopted on others. Proxygate uses USDC on Solana for its prepaid escrow and exposes an x402 top-up flow that returns a signable Solana deposit transaction.