The web finally has a way to charge by the request.

The client can be anything that speaks HTTP: a browser with a wallet extension, a script, an AI agent running autonomously, or another server. The initial request looks identical to any other HTTP request — no special headers, no payment information attached. The server decides whether the resource is paid or free; the client doesn't need to know in advance.

This is one of x402's design strengths: existing HTTP clients don't need to be rebuilt from scratch. Any client that can add a header to a request can participate in the x402 payment flow.

The 402 response body contains a structured payment payload: the amount (in USDC or another supported stablecoin), the blockchain network to pay on (Base, Solana, or others), the wallet address to send to, and a time window within which the payment must be made. It also includes a nonce — a unique value that prevents the same payment being reused for multiple requests.

The HTTP status code 402 ("Payment Required") was reserved in the original HTTP specification in 1991 but never formally used until x402 gave it a concrete meaning. Every browser and server already understands the status code — the protocol adds the payment payload on top of existing infrastructure.

The client uses EIP-3009 (transferWithAuthorization) to sign a USDC transfer matching the exact terms from the 402 response — same amount, same recipient, same network. The signature is attached to the retried request in the X-PAYMENT header as a base64-encoded token.

Critically, the client doesn't need to broadcast a transaction to the blockchain at this point — the signed authorization is just a cryptographic proof of intent. The actual on-chain transfer happens in the next step, handled by the facilitator. This keeps the client-side flow simple and fast.

When the server receives the retried request with the X-PAYMENT header, it passes the signed authorization to a facilitator — a service that submits the transaction to the blockchain, waits for confirmation, and returns a settlement receipt. Once the facilitator confirms payment, the server delivers the resource with a 200 OK response and an X-PAYMENT-RESPONSE header confirming settlement.

On Base, this settlement typically takes 1–3 seconds. On Solana, closer to 400 milliseconds. The facilitator handles all the blockchain interaction so neither the server nor the client needs to run their own blockchain infrastructure.

Credit card processing has fixed costs — typically $0.20–0.30 per transaction plus a percentage — that make charging less than around $1 economically irrational. This is why the web defaulted to subscriptions and advertising: there was no viable way to charge small amounts for individual pieces of content or API calls.

x402 settles on Layer 2 blockchains where transaction costs are fractions of a cent. A payment of $0.001 is now economically viable, opening up pricing models that were never possible before: pay-per-article, pay-per-API-call, pay-per-second-of-compute. For AI agents making hundreds of calls per session, this changes the economics of what's worth building.

Coinbase published the original x402 specification in May 2025. In April 2026, governance transferred to the x402 Foundation, hosted under the Linux Foundation — the same neutral governance model used by Linux, Kubernetes, and other major open infrastructure projects. This means no single company can unilaterally change the protocol or lock in proprietary advantages.

Foundation members include Google, Visa, Stripe, AWS, Mastercard, American Express, Cloudflare, Circle, Shopify, and Fiserv — a coalition broad enough to signal that this is becoming shared internet infrastructure rather than one company's product. The protocol specification is open source and available on GitHub.