x402, a protocol enabling autonomous AI agents to make micropayments without API keys or subscriptions, is now live on Stellar. The protocol uses HTTP 402 status codes to facilitate instant stablecoin payments, with Stellar chosen as the settlement layer due to its speed, low fees, and reliability.
x402 is a payment protocol that solves a critical problem for autonomous AI agents: enabling them to pay for services (APIs, compute, data) without pre-configured credentials or human intervention. Launched by Coinbase in May 2025 and now supported by a foundation including Google and Visa, x402 has processed millions of payments. The protocol works by having a server respond to a client request with a price, the client authorizes a stablecoin payment, and the resource is delivered—all within one HTTP round-trip. Stellar was selected as the settlement layer because it offers sub-5-second settlement, near-zero transaction fees (approximately $0.00001), native stablecoin support (USDC, PYUSD, USDY), 99.99% uptime, and programmable smart contracts via Soroban. The article includes code examples for implementing x402 on Express APIs and outlines upcoming features like MCP integration and embedded smart wallets for agent-native tooling.
