Agent & API Payments

x402 is the leading candidate for the agent-economy payment rail: it lets an AI agent (or any HTTP client) pay for an API call inline, with no API key, no signup, and no human-in-the-loop. If you're building agentic apps, paid MCP servers, per-request data products, or anything where "charge for this request without a session" matters, x402 is the standard to know — supported by Coinbase, Cloudflare, Vercel AI Gateway, and a growing facilitator ecosystem.

If you're returning 402 — or shopping for a way to monetize an API or MCP server — the spec hands you the code and nothing else. The meaning lives entirely in whatever protocol you layer above it: x402 (stablecoins, X-PAYMENT header), L402 (Lightning, WWW-Authenticate macaroon+invoice), or your own. Knowing that 402 itself is a blank canvas is the difference between shipping an interoperable agent-payable endpoint and a 402 response no client can negotiate against.

L402 is the Bitcoin-native counterpart to x402: same HTTP 402 surface, but settled off-chain on Lightning instead of on-chain via stablecoins. Useful when you need true micropayments (sub-cent), instant finality without facilitators, and Bitcoin economics. Powers paid LLM access (e.g. Fewsats), paid storage gateways, and a small but real ecosystem of metered Lightning APIs.