Your agent needs an API. The normal options are all built for humans: sign up, verify an email, add a credit card, get an API key, pick a subscription tier, pay for 10,000 calls to use 17 of them.

There is a fourth option, and it is 30 years old: HTTP status code 402 Payment Required was reserved in the original HTTP spec "for future use." The future arrived. The x402 protocol (v2, stewarded by Coinbase) turns 402 into a working payment handshake: the server answers with a price quote, the agent signs a stablecoin payment authorization, a facilitator settles it on-chain, and the API responds — no accounts, no keys, no subscriptions. Payment is the authentication.

This is not a whitepaper tour. Everything below runs against a live store ( call402.com ) where 15 small APIs — FX rates, phone/email validation, SEC company facts, text structuring, and more — are sold per call for $0.002–$0.005 USDC on Base.…