✨x402✨ HTTP 402, "payment required," has been sitting in the spec since 1997. for nearly three decades it did nothing because there was no standard for what a machine should actually do when it received one. no protocol for how to format the request, negotiate the price, or settle the transaction. in may 2025, @CoinbaseDev shipped x402, an open protocol that finally gives that status code a job. an agent sends a request. the server responds with 402 plus machine-readable payment terms: amount, asset, network, recipient. the agent evaluates the price, signs a stablecoin transaction, and retries with a payment proof header. just HTTP semantics and cryptographic proof of payment. the adoption curve has been steep. by the end of 2025, x402 had processed over 100 million payment flows across APIs, apps, and autonomous agents. @cloudflare co-launched the x402 foundation in september 2025 to formalize open governance of the standard. stripe started using x402 to facilitate USDC payments for AI agents on base in february 2026. @googlecloud's agent payments protocol uses x402 for onchain settlement. the protocol now operates across @base, @solana, and @0xPolygon. V2 shipped in december 2025 with wallet-based identity, automatic API discovery, multi-chain support via CAIP standards, and compatibility with legacy payment rails like ACH and card networks. x402 went from open source experiment to foundational infrastructure in under a year. x402 = the payment primitive for agent commerce.