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ACP vs UCP vs AP2 vs MCP: which agentic commerce protocol does your store need?

ACP, UCP, AP2 and MCP compared as of October 2026: what each does, who backs it, where it is live and which one your store actually needs.

By the ConversionVector teamUpdated 12 min read

Contents

Direct answer: As of October 2026 the four protocols do different jobs. ACP (Agentic Commerce Protocol, maintained by OpenAI and Stripe, in beta) and UCP (Universal Commerce Protocol, co-developed by Google, Shopify and a long list of retailers and platforms) both define how AI agents and businesses exchange product data and complete purchases while the business stays merchant of record. AP2 (Agent Payments Protocol) proves that a user authorised an agent to pay. MCP (Model Context Protocol) is a general way for AI apps to call tools, and commerce protocols can run over it. UCP sits behind the most live checkout channels today: Google's checkout in AI Mode and Gemini, Google's Universal Cart, Microsoft Copilot Checkout and TikTok's Buy Direct test. Most retailers should not build any of these by hand. Use your platform's or payment provider's route, and first fix the feeds, structured data and access that every protocol depends on.

This guide is for CTOs, developers and ecommerce directors deciding what to implement and what to defer. It covers what each protocol is, where it is live by market, how the four fit together and a decision table by platform and market.

Last verified: 28 October 2026 against the ACP repository on GitHub, OpenAI's commerce documentation and merchants page, ucp.dev and its announcements page, Google Merchant Center Help and Google's UCP developer guides, Microsoft Advertising's agentic commerce page, Shopify's Help Center, ap2-protocol.org and the MCP specification. These change often, so check the current versions before you plan work.

The four protocols at a glance

ACPUCPAP2MCP
Full nameAgentic Commerce ProtocolUniversal Commerce ProtocolAgent Payments ProtocolModel Context Protocol
JobCheckout between agent and merchant, plus product feedsCommerce lifecycle: catalogue, cart, identity linking, checkout, ordersProof that the user authorised a purchase and paymentGeneral connection between AI apps and tools or data
Who runs it"Maintained by OpenAI and Stripe"Co-developed by Google, Shopify, Etsy, Wayfair, Target, Walmart and others, with a governing councilOpen protocol; standardisation continues in FIDO Alliance working groupsOpen protocol with its own specification
Status (28 Oct 2026)"Currently in beta"; latest dated release 2026-04-17Dated releases; latest v2026-08-25v0.2Latest version 2026-07-28
Live merchant channelsChatGPT product feeds (shopping live for US users); purchases complete on merchants' sites or appsGoogle AI Mode and Gemini checkout (select merchants; US, Canada and Australia eligibility), Universal Cart (US), Copilot Checkout (US buyers, USD), TikTok Buy Direct (test)Through UCP and payment providersMany tools; not a shopping channel by itself
Score checkTRX-05TRX-04(none)TRX-06
Primary sourceGitHubucp.devap2-protocol.orgmodelcontextprotocol.io

The check IDs are from the Agent Conversion Score specification v0.6: TRX-04 is "/.well-known/ucp business profile present and valid", TRX-05 is "ACP discovery (/.well-known/acp.json) or ACP product feed present" and TRX-06 is "MCP endpoint advertised". The free Agent Conversion Score runs all three, alongside the access, data and checkout checks every protocol depends on.

ACP: OpenAI and Stripe's checkout and feed protocol

What it is. The ACP repository describes "an interaction model and open standard for connecting buyers, their AI agents, and businesses to complete purchases seamlessly". The specification is "maintained by OpenAI and Stripe and is currently in beta", under the Apache 2.0 licence.

Releases. The repository lists dated versions: 2025-09-29 (initial release), 2025-12-12 (fulfilment), 2026-01-16 (capability negotiation), 2026-01-30 (extensions, discounts, payment handlers) and 2026-04-17 ("cart, feed, orders, authentication, and MCP"). Work since then sits in an unreleased folder; there has been no new dated release since April.

How OpenAI uses it. OpenAI's commerce documentation includes an Agentic Checkout spec for merchants, a Delegated Payment spec for payment providers, and product feed specs. The Get started guide says: "Start your ACP integration by sharing a structured product feed with OpenAI." It also says onboarding product feeds "is currently available to approved partners", through an application form.

What changed. OpenAI launched in-chat Instant Checkout, "powered by the Agentic Commerce Protocol, built with Stripe", on 29 September 2025. Its merchants page now says: "We're moving away from a standalone Instant Checkout experience in ChatGPT… purchases are completed on merchant-owned websites or apps." The same page says that today ACP "supports product discovery and more accurate, personalized recommendations through shared product data", that shopping "is currently live for ChatGPT users in the U.S.", and that stores selling through Shopify or Etsy are already integrated. So the protocol is alive, but the in-chat purchase it first powered is not how ChatGPT works today.

Who should care. Any retailer that wants to appear in ChatGPT shopping should care about the feed side. Read OpenAI's Merchant Feed Terms before you apply, because they now cover crawler and agent access. The checkout side matters only if your platform or payment provider offers it. WooCommerce, for example, lists ACP through Stripe's Agentic Commerce Suite as "coming soon" (see our WooCommerce checklist).

UCP: the broad coalition protocol

What it is. UCP calls itself "the common language for platforms, agents, and businesses". The co-developers it lists for shopping include Google, Shopify, Etsy, Wayfair, Target, Walmart, Amazon, Microsoft, Meta, Salesforce and Stripe. It says businesses "retain control and remain the Merchant of Record".

What it covers. Catalogue search and lookup, cart building, identity linking, checkout and order management. It runs over "REST and JSON-RPC transports", with "Agent Payments Protocol (AP2), Agent2Agent (A2A), and Model Context Protocol (MCP) support built-in". A business publishes a profile at /.well-known/ucp so agents can discover what it supports. The protocol is also expanding beyond retail: a lodging booking draft was released on 25 September 2026 and the site says food is "coming soon".

Releases and governance. The announcements page lists protocol releases v2026-01-11, v2026-01-23, v2026-04-08 and v2026-08-25. The last of these brought "major protocol enhancements", "payments security improvements (3DS2)" and "independent capability versioning". It also records Stripe joining the governing council alongside Google and Shopify (28 April 2026) and the formation of a Payments Technical Council (2 September 2026). There is a public conformance test repository.

Live channels.

  • Google AI Mode and Gemini. Merchant Center Help says its UCP article "only applies to products with eligibility in the United States, Canada, and Australia", and that the checkout feature "is available for select merchants at this time", through an interest form (Merchant Center Help). Google's developer guide says the UCP integration hub in Merchant Center "is gradually rolling out in the United States, with Australia and Canada to follow early next year" (Google for Developers, updated 19 October 2026). On 20 May 2026 Google said UCP-powered checkout "will roll out across Canada and Australia in the coming months, and later to the U.K." (Google). Checkout happens on Google's surface with Google Pay, and you stay merchant of record. Products opt in with the native_commerce(checkout_eligibility) attribute, which "defaults to FALSE"; Google recommends a supplemental data source for it (Google for Developers).
  • Google Universal Cart. Launched in the US on 15 October 2026 across Search and the Gemini app, with checkout "powered by the Universal Commerce Protocol (UCP)" (Google). Our Universal Cart guide covers the cart-transfer route.
  • Microsoft Copilot Checkout. Microsoft Advertising says Microsoft Merchant Center "will support Universal Commerce Protocol (UCP)" and describes UCP as "a complementary layer to Merchant Center feeds": feeds "primarily enable discovery", while UCP "enables transactions". Eligibility: "Only English‑language merchants who sell to US buyers are eligible at this time (supporting USD)." You can onboard through Microsoft Merchant Center or through PayPal or Stripe, and Shopify merchants "have been automatically enrolled". Microsoft says it "cannot provide a timeline" for other regions (Microsoft Advertising).
  • TikTok Buy Direct. TikTok says its new in-app checkout "requires an integration with Universal Commerce Protocol (UCP)". It is a test for selected advertisers; see our TikTok Buy Direct guide.
  • Shopify. Shopify merchants reach Google AI Mode and Gemini through agentic storefronts, with no custom build. Shopify's Help Center says you "must sell to customers in the United States, Canada, or Australia" and that your "store can be based in any country". Direct checkout is "activated by default for eligible stores" and "rolling out gradually to customers based in the United States, Canada, and Australia".

What we see in the Index. When we fetched /.well-known/ucp from the 225 retailers scored in our Agent Commerce Index on 28 October 2026, 121 served a profile, and 115 of those were Shopify stores. Most of the UCP profiles in the wild today come from the platform, not from a retailer's own build. The method and the breakdown are in our TikTok Buy Direct guide.

AP2: the payments trust layer

What it is. AP2 is "an open protocol for the emerging Agent Economy". It is built to answer three questions when an agent pays: authorisation, authenticity and accountability. It is "available as an extension for the open-source Agent2Agent (A2A) protocol and Universal Commerce Protocol with more integrations in progress".

How it works. AP2 uses signed "verifiable digital credentials" called mandates. A Checkout Mandate captures the items and purchase details agreed between the agent and the merchant. A Payment Mandate authorises payment against a specific payment instrument. Each exists in two stages: open (the user's constraints and goals, such as a budget, set before a specific cart is final, for autonomous execution) and closed (authorisation of a specific, finalised checkout). Chained together they give an audit trail for both human-present and human-not-present purchases.

Status. AP2 was announced on 16 September 2025. The site lists a v0.2 release and a donation to the FIDO Alliance, and says standardisation "will continue within the Agentic Authentication Technical and Payments Technical Working Groups in FIDO". The initial version supports card "pull" payments. The roadmap includes e-wallets, real-time bank transfers "such as UPI and PIX" and digital currencies, which matters in markets where cards are not dominant.

Who should care. Payment providers, networks and agent builders. As a retailer, you will meet AP2 through your payment provider or through UCP rather than implementing it.

MCP: the general tool layer

What it is. The MCP specification describes "an open protocol that enables seamless integration between LLM applications and external data sources and tools". It uses JSON-RPC 2.0 messages, and servers expose resources, prompts and tools. The latest version is 2026-07-28.

How it relates to commerce. MCP is a transport for capabilities, not a commerce model. UCP lists MCP support as built in, and ACP's 2026-04-17 release added MCP. Platforms also ship MCP servers for running a store. WooCommerce says its MCP integration "helps AI assistants manage a store (finding, adding, and updating products and orders), not check out shoppers" (WooCommerce). WebMCP is a separate, browser-side proposal that lets a page expose tools to an agent in the shopper's browser; see WebMCP for ecommerce.

Security. The specification warns that "tools represent arbitrary code execution and must be treated with appropriate caution". If you expose an MCP server, scope it tightly and never give it more permission than the task needs.

How they fit together

Shopper ──> AI assistant (ChatGPT, Gemini, Copilot, TikTok, ...)
                │
                ├── discovery:  product feeds (Google and Microsoft Merchant Center, ChatGPT feeds)
                │               + your pages and structured data
                │
                ├── checkout:   UCP or ACP session with your store (or your platform)
                │                   └── payment authorisation: AP2 mandates / PSP tokens
                │
                └── transport:  REST, JSON-RPC or MCP

Two points follow from this:

  1. Discovery comes before every protocol. Every live route above starts from a product feed or your pages. A protocol endpoint in front of a store that agents cannot read does nothing.
  2. ACP and UCP overlap. AP2 and MCP do not compete with them. You might support both UCP and ACP. AP2 and MCP sit underneath or alongside them.

Which one do you need? By market and platform

Your situation (28 Oct 2026)What to do
Shopify store selling to the US, Canada or AustraliaCheck your agentic storefront settings (Sales channels > Agentic). Shopify says Google direct checkout is on by default for eligible stores and is rolling out to shoppers in those three countries. Microsoft says Shopify merchants are enrolled in Copilot Checkout automatically (US buyers only). Shopify handles the UCP side
Non-Shopify store selling to US buyersGet into Google Merchant Center and Microsoft Merchant Center. Register interest in Google's UCP checkout. Ask your payment provider (Stripe, PayPal) about Copilot Checkout. Apply for ChatGPT feeds
Selling into Canada or AustraliaMerchant Center in good standing; register interest in Google's UCP checkout (Google says its integration hub reaches these markets "early next year"). Add native_commerce(checkout_eligibility) in a supplemental data source when you are accepted
UK, EU or rest of worldNo Google, Microsoft or ChatGPT in-chat checkout for your home market yet; Google has said the UK comes after Canada and Australia, with no date, and we found no EU date. Fix feeds, structured data, access and checkout friction so you are ready when one opens. If you also sell to US, Canadian or Australian buyers, the routes above may apply
WooCommerce, Adobe Commerce, BigCommerce, Salesforce or customAsk your platform or payment provider about its official route and timeline. Treat early third-party plugins as experiments, and test them on staging
Enterprise with in-house engineeringConsider a direct UCP implementation against a dated version, using the public conformance tests. Watch ACP if ChatGPT matters to you

What to fix first

  1. Access. Agents must reach your pages and checkout. See Are you blocking AI shopping agents?.
  2. Feeds. Google Merchant Center first, then Microsoft Merchant Center and ChatGPT feeds. Every live channel above starts there.
  3. Structured data and policies. Price, stock, shipping and returns, machine-readable. See Product structured data for AI agents.
  4. Checkout friction. Guest checkout, no captcha for verified agents, a server-rendered basket. See Page-fetching vs browsing agents.
  5. Then a protocol, through your platform or payment provider where possible.

Common mistakes

  • Treating "MCP-enabled" as "agent checkout". MCP is plumbing. Ask what capabilities it exposes and to whom.
  • Building to one protocol version and forgetting it. UCP shipped four dated releases between January and August 2026, and ACP has five dated releases since September 2025. Budget for upgrades.
  • Assuming ACP is dead. The in-chat Instant Checkout experience changed. The protocol and its feeds did not go away.
  • Assuming in-chat checkout is global. As of 28 October 2026 it is mostly US, with Google's eligibility extending to Canada and Australia and the UK promised later.
  • Confusing a UCP profile with a live integration. A /.well-known/ucp profile declares what you support. Google's checkout still needs acceptance into its programme and the eligibility attribute on your products.
  • Implementing AP2 as a merchant. It reaches you through your payment provider.

Sources

Questions

What is the difference between ACP, UCP, AP2 and MCP?
ACP (maintained by OpenAI and Stripe) and UCP (co-developed by Google, Shopify and others) both define how AI agents and businesses exchange product data and complete purchases, with the business staying merchant of record. AP2 is a payments layer that proves a user authorised an agent to pay. MCP is a general way for AI applications to call tools and data, and is not specific to commerce.
Which protocol should a retailer implement first?
For most retailers, none directly. Use the route your platform or payment provider offers. As of 28 October 2026, UCP sits behind the most live checkout channels: Google's UCP-powered checkout in AI Mode and Gemini (available to select merchants, with eligibility covering the US, Canada and Australia, and the UK later), Google's Universal Cart (US), Microsoft Copilot Checkout (US buyers) and TikTok's Buy Direct test. Before any protocol, fix product feeds, structured data and agent access.
Is ACP still used now OpenAI has moved away from Instant Checkout?
Yes. The ACP specification is still maintained by OpenAI and Stripe and is in beta; its latest dated release is 2026-04-17. OpenAI's Get started guide says to start an ACP integration by sharing a product feed, and its merchants page says ACP today supports product discovery and recommendations. What changed is that ChatGPT purchases are now completed on merchants' own sites or apps rather than in a standalone in-chat checkout.
Do I need AP2?
Not directly, as a retailer, today. AP2 is aimed at agents, payment providers and networks. It is available as an extension for UCP and A2A, and its standardisation continues in FIDO Alliance working groups. You will usually meet it through your payment provider.
Does MCP let AI agents buy from my store?
Not on its own. MCP lets an AI application call tools you expose. UCP lists MCP support as built in and ACP's 2026-04-17 release added MCP, but a generic MCP server is not a checkout channel. WooCommerce, for example, says its MCP integration helps AI assistants manage a store, not check out shoppers.

Published . Last updated . More in Agentic commerce and the guide library.

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