x402 protocol

Also known as: HTTP 402 payment protocol, x402, x402 Foundation protocol

An open HTTP standard that lets AI agents pay for API access programmatically, without accounts or checkout flows. A server responds with a 402 status and payment terms; the agent pays and retries, all in one request cycle.

When an AI agent needs to call a paid API, the current answer is usually a human-managed API key tied to a billing account. That breaks down fast as agents multiply and start making thousands of micro-calls across dozens of services. The x402 protocol is an attempt to fix this at the protocol level: a server signals 'payment required' using the long-dormant HTTP 402 status code, the agent reads the machine-readable payment terms and pays, then retries the request. No login, no subscription form, no card entry.

The protocol was originally developed by Coinbase and contributed to the Linux Foundation, which launched the x402 Foundation as a formal governance body on July 14, 2026, with 40 founding members including Visa, Mastercard, Stripe, Google, AWS, and Cloudflare. Settlement today runs primarily on USDC, though the protocol is designed to be chain-agnostic and also supports traditional card payments.

For builders, x402 matters most as a foundational primitive for the 'agentic economy': the set of infrastructure patterns that emerge when AI agents become first-class economic actors that spend money to get work done. It sits alongside MCP (which handles tool access) as a protocol-layer answer to a question that product-layer solutions can't fully solve.

This definition is AI-generated and refreshed weekly. It may contain inaccuracies. Use your own judgment, especially for production decisions.

Related terms