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Agentic Commerce ProtocolsOverview

Agentic Commerce Protocols at xpay✦

Three open specifications are defining how AI agents transact with merchants on behalf of humans. They overlap heavily and will probably converge on parts of their surface area; for now they’re worth understanding separately:

  • ACP — Agentic Commerce Protocol, maintained by OpenAI and Stripe.
  • UCP — Universal Commerce Protocol, a vendor-neutral effort with a Tech Council + Governance Council.
  • AP2 — Agent Payments Protocol, Google’s contribution centered on Agent-to-Agent (A2A) flows.

This section documents each protocol on its own terms, then puts them side-by-side in a single technical comparison page:

xpay✦ contributes upstream to ACP and UCP, runs an MCP server for tool discovery, and integrates with multiple payment rails so merchants aren’t locked into one. The commerce protocols below are rail-agnostic by design — pick the cart/checkout semantics that fit, then plug in whatever payment rail your buyers use.

How the layers fit

  • MCP is how agents discover and call tools.
  • ACP / UCP / AP2 define what those tools mean (a cart, a checkout, an order).
  • Payment rails are how the agent pays once a checkout returns a price. Rail choice is independent of the commerce protocol: cards, stablecoins via x402, Stripe’s MPP , Adyen, ACH, whatever fits the merchant.

Mix and match freely. ACP today assumes server-side processors (Stripe, Adyen). UCP’s MCP binding composes cleanly with any rail. AP2 leans on Google’s A2A transport and is itself rail-agnostic.

For merchants

Just want to accept agent-driven purchases without picking a protocol yourself?

Where to go next

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xpay FacilitatorACP vs UCP vs AP2