Protocols

Which rails can agents pay over?

Several payment rails carry agent purchases today, and no winner has been declared. We don’t declare one either. Each rail below gets the same page template at the same depth, and the four appear in one alphabetical order on every surface of this site — described, never ranked.

• AP2 & UCP

  A Google-backed pair: AP2 authorizes agent spending through signed mandates; UCP carries the wider shopping flow — discovery, offers, checkout.

• Stripe machine payments

  Stripe’s rails for software buyers: agents pay in stablecoins or by card, through payment credentials scoped to a single agent.

• Verifiable Intent & Agent Pay

  Mastercard’s card-network approach: provable buyer authorization (Verifiable Intent) paired with a program for agent-initiated payments (Agent Pay).

• x402

  An open protocol that revives the web’s dormant 402 status code so services can charge machines per request. Stewarded by the x402 Foundation.

Want them side by side? The comparison matrix puts all four in one table — backers, money type, authorization, receipts, disputes, status — with every cell cited to a primary source.