x402

An open payment protocol (originated by Coinbase, 2025) that revives HTTP status code 402 “Payment Required”: a server quotes a price in a response header, the client — typically an agent — pays, usually in stablecoins, and retries the request with proof of payment. Built for machine-speed micropayments: pay-per-request APIs, pay-per-crawl content, sub-cent prices with no accounts or card forms. Its open question is everything the header omits: disputes, refunds, and who eats a wrong purchase.