x402 is an open standard for paying over HTTP. It reuses the long-dormant 402 Payment Required status code so a server can quote a price and a client can pay for a gated resource inside a normal web request — no checkout page, no stored card, no human login. It was designed for machine-to-machine payments: an AI agent, app, or crawler requests a page, dataset, API, or product, receives a 402 stating the price and where to pay, pays, and retries with proof attached.
The handshake is the whole idea: request → 402 with price and accepted asset → pay → retry with proof → resource returned. Because it lives inside ordinary HTTP, any compatible server can charge and any x402-speaking client can pay, without a bespoke billing integration. That suits the sub-cent, high-frequency payments AI agents generate — territory where the ~$0.30 card-fee floor makes traditional rails uneconomic.
Coinbase originated x402 as a stablecoin-native scheme (USDC on Base). On 14 July 2026 the Linux Foundation launched the x402 Foundation to steward it under vendor-neutral governance, with 40 members including Google, Stripe, Visa, Mastercard, Cloudflare, and Coinbase. The standard is written to be payment-type-agnostic — spanning cards to stablecoins — though most live settlement today runs in stablecoins.
x402 is a payment-request layer, not a checkout experience or a settlement rail. It sits below the Agentic Commerce Protocol (which orchestrates an order inside an assistant) and above the card and stablecoin rails (which move the money). One notable use beyond commerce: it makes charging an AI crawler for access — pay-per-crawl — a real option between allowing and blocking. Figures and membership are dated to mid-2026 and will move.