ACP vs AP2 vs UCP vs x402: the agentic commerce protocols, compared

The agentic commerce stack has four major protocols plus MCP, and they solve different problems: ACP and UCP handle checkout and catalog, AP2 handles authorization, and x402 handles machine-native payments. Most businesses will end up needing several at once.

The comparison at a glance

Protocol	Steward	Layer	Solves	Status (mid-2026)
ACP	OpenAI + Stripe	Checkout	Purchases inside ChatGPT and ACP-compatible agents	Live; powers ChatGPT Instant Checkout
UCP	Google	Catalog + cart + identity	Real-time product queries and cart building	Live; expanded through 2026
AP2	Google + 60 partners	Authorization	Signed proof the user approved intent and cart	Rolling out across networks
x402	Coinbase	Payment	HTTP-native stablecoin payments, micropayments	V2 shipped; Stripe integration on Base
MCP	Anthropic (open)	Tooling	How agents discover and call your capabilities	De facto standard for tool access

What does each protocol actually do?

ACP (Agentic Commerce Protocol) is an open spec from OpenAI and Stripe that lets an agent fetch your catalog, build a cart, and complete checkout. It is the protocol behind Instant Checkout in ChatGPT, launched with Etsy and Shopify merchants. If your customers use ChatGPT, ACP is how they buy from you inside it.

UCP (Universal Commerce Protocol) is Google’s commerce surface, announced at NRF in January 2026. It added Cart, Catalog with real-time product queries, and Identity Linking by March 2026. It plays the same role for Gemini surfaces that ACP plays for ChatGPT.

AP2 (Agent Payments Protocol) is not a checkout protocol; it is a trust layer. It defines cryptographically signed “mandates”: an intent mandate (“find me dinner under $50”) and a cart mandate (“charge $41.80 for this order”). The mandate travels with the payment, so merchants and issuers can prove the human authorized the transaction.

x402 revives HTTP status 402 (Payment Required) for machine-to-machine payments in stablecoins. It matters most for API metering, pay-per-call pricing, and agent-to-agent settlement rather than retail checkout.

MCP (Model Context Protocol) is how agents see your business as callable tools: search_catalog, get_quote, book, buy. Every major model provider now supports MCP clients, which makes an MCP server the most portable agent surface you can publish.

Which protocol should a merchant integrate first?

The uncomfortable answer: the protocol war is not settled, and the stewards are competitors. Card networks hedged the same way; Visa’s Intelligent Commerce Connect explicitly supports TAP, ACP, and UCP behind one integration.

For an individual business, hand-integrating four evolving specs is a poor use of engineering time. The practical pattern in 2026 is aggregation: integrate once with infrastructure that publishes all of the above and tracks spec changes for you. That is the design premise of Errand: your catalog, checkout, and booking flow published simultaneously as ACP, UCP, and MCP surfaces with AP2 mandates verified on every order.

Frequently asked

Do ACP and AP2 compete? No. ACP moves the order; AP2 proves it was authorized. A single purchase can, and increasingly does, use both.

Is x402 relevant if I do not accept crypto? Mostly no for retail today. It becomes relevant if you sell API access or usage-priced services to agents.

Will one protocol win? History suggests convergence rather than a single winner; payments still run on multiple card networks decades in. Building against an abstraction layer is the hedge.