x402

x402 is Coinbase's revival of the long-dormant HTTP 402 "Payment Required" status code. Open spec under Apache 2.0. The mechanism: a client requests a resource; the server replies 402 with payment instructions referencing an on-chain stablecoin payment (USDC primarily); the client pays; the server returns the resource on confirmation. Released in 2025 and donated to the Linux Foundation. x402 matters because it is the on-chain-settlement counterpart to L402's Lightning-anchored approach to the same problem (paying for agent-accessed resources without an account). The design choice is the interesting tradeoff: Lightning offers sub-second settlement and very low fees but locks you to the Bitcoin ecosystem; on-chain stablecoin settlement is more familiar to web2 builders and integrates with existing payment infrastructure but settles slower and has higher per-tx fees. Compared to L402 (Lightning, Bitcoin-anchored, longer track record), x402 (stablecoin, web2-friendlier, newer), and Stripe Agent SDK (closed, very polished, ties you to Stripe). Production-readiness: shipping and adopted by a growing set of AI infrastructure providers. Stripe announced an x402 integration in 2026, which is a strong signal of acceptance at the payments-incumbent layer. The strategic question for x402 and L402 jointly: which agentic-payment rail wins matters more than people realize, because the rails determine who can become an economic agent in the agentic web without permission.