What Is x402?

x402 is an open protocol that uses the long-dormant HTTP 402 ("Payment Required") status code to let a server request an on-chain stablecoin payment from a client — human or AI agent — before returning a resource, without redirects, accounts, or API keys.

Key facts

• Initiated by Coinbase Developer Platform. The x402 whitepaper, titled "x402: An open standard for internet-native payments," was published on May 6, 2025, authored by Erik Reppel, Ronnie Caspers, Kevin Leffew, Danny Organ, Dan Kim, and Nemil Dalal of Coinbase Developer Platform.
• Core mechanism: three roles over HTTP. Per the x402 FAQ, a transaction involves a client (the payer), a resource server (the API/service being paid for), and a facilitator (a third party that verifies and settles the payment on-chain). Anyone can run a facilitator — the protocol is described as "permissionless."
• Settlement networks and assets. x402 supports Base (mainnet and Sepolia testnet) and Solana (mainnet and Devnet), accepting any ERC-20 token on Base and any SPL or Token-2022 token on Solana, with fee-free settlement, per docs.x402.org.
• Open-source license: Apache-2.0. Confirmed on the coinbase/x402 GitHub repository and in the docs FAQ.
• Governance has moved to the Linux Foundation. The x402 Foundation had its operational launch on July 14, 2026, with premier members including Adyen, AWS, American Express, Circle, Cloudflare, Coinbase, Fiserv, Google, Mastercard, Monad Foundation, MoonPay, Ripple, Shopify, Solana Foundation, Stellar Development Foundation, Stripe, and Visa, per the Linux Foundation's press release.

How it works

1. A client (often an AI agent or automated script) sends an HTTP request to a resource server for a paid API call, data feed, or piece of content.
2. Instead of returning the content, the server responds with HTTP status 402 Payment Required, including machine-readable payment requirements (amount, accepted asset, network, recipient address).
3. The client constructs and cryptographically signs a payment matching those requirements — no OAuth flow, account creation, or stored card is needed.
4. The client resends the request with the signed payment attached; a facilitator verifies the signature and settles the payment on-chain (e.g., a USDC transfer on Base).
5. Once settlement is confirmed, the resource server fulfills the original request and returns the content or API response.
6. Because every payment is signed by the payer and settled on-chain, a facilitator cannot alter or redirect funds — tampering causes the signature check to fail, per docs.x402.org.

x402 vs. AP2 vs. ACP

FAQ

What does "402" refer to? HTTP status code 402, reserved in the original HTTP specification for "Payment Required" but left unused for decades until x402 defined a standard way to use it, per the x402 whitepaper.

Do I need a Coinbase account to use x402? No. x402 is a protocol, not a Coinbase product account — any wallet capable of signing a compatible payment can act as a client, and anyone can run a facilitator, per docs.x402.org.

Which blockchains does x402 support? Base (mainnet and Sepolia testnet) and Solana (mainnet and Devnet), per docs.x402.org. Support may expand as the x402 Foundation grows.

Is x402 still controlled by Coinbase? No longer solely. It moved to the vendor-neutral x402 Foundation under the Linux Foundation, with its operational launch on July 14, 2026, per the Linux Foundation announcement.

Can x402 be used with AP2? Yes, in part. Google's AP2 announcement describes an x402 extension co-developed with Coinbase, the Ethereum Foundation, and MetaMask for crypto/stablecoin payments within AP2, per the Google Cloud blog.

Related terms

• Agentic payments
• Agent Payments Protocol (AP2)
• Agentic Commerce Protocol (ACP)
• AI agent wallet