Short answer: The four protocols work at different layers. MCP is the general plumbing that connects AI apps to tools and data. UCP (Google and Shopify) and ACP (OpenAI and Stripe, with Meta) are competing commerce languages for catalog, cart and checkout. WebMCP lets a web page expose tools to AI agents running inside the browser. Shopify implements UCP and WebMCP natively.
All four changed between August and October 2026. UCP shipped a major release and powered Google's native checkout for Shopify merchants. WebMCP went live on every Shopify Liquid storefront and then on checkout. MCP finalized discovery and Skills extensions. ACP did not ship a new version. This comparison is written for Shopify Plus teams deciding where to spend development time before the holidays.
The comparison at a glance
|
UCP |
ACP |
WebMCP |
MCP |
| Full name |
Universal Commerce Protocol |
Agentic Commerce Protocol |
WebMCP (browser API) |
Model Context Protocol |
| Created by |
Google and Shopify (Jan 11, 2026) |
OpenAI and Stripe (Sep 29, 2025) |
Microsoft and Google |
Anthropic (2024) |
| Governed by |
UCP Governing Council (Google, Shopify permanent; Stripe joined Apr 2026) |
OpenAI, Stripe and Meta as lead maintainers |
W3C Web Machine Learning Community Group (draft, not standards track) |
Agentic AI Foundation, under the Linux Foundation |
| Layer |
Commerce: discovery, catalog, cart, checkout, identity, orders, payments |
Commerce: checkout, delegated payment, cart, product feeds, orders |
Browser: page exposes JavaScript tools to in-browser agents |
Transport: connects AI apps to tools and data |
| Latest version |
v2026-08-25 |
2026-04-17 (beta) |
Draft report dated Oct 9, 2026 |
2026-07-28 |
| Changed Aug–Oct 2026? |
Yes, major release and new councils |
No new release |
Yes, API changes; declarative API removed Oct 8 |
Yes, roadmap and finalized extensions; no new spec version |
| Shopify support |
Native. Storefronts advertise v2026-08-25 |
Not Shopify's checkout path; ChatGPT refers buyers to your checkout |
Native on Liquid storefronts (Aug 5) and checkout (Sep 28) |
Shopify's agent endpoints run UCP over MCP |
| Used by |
Google AI Mode, Gemini, Microsoft Copilot |
ChatGPT (discovery and feeds) |
Chrome and Edge origin trials, ChatGPT Desktop, Brave Leo |
Nearly every AI assistant and coding agent |
UCP (Universal Commerce Protocol)
What it is. UCP is an open standard for the full agent shopping flow: discovery through a business profile at /.well-known/ucp, catalog search, cart, checkout, identity linking, order management and payment handlers. It runs over REST and JSON-RPC, with built-in support for MCP, A2A and Google's AP2 payment protocol (Google Developers Blog, ucp.dev).
Who backs it. Google co-developed UCP with Shopify, Etsy, Wayfair, Target and Walmart. The current list of shopping co-developers on ucp.dev also includes Amazon, Microsoft, Meta, Salesforce and Stripe.
What changed August to October 2026:
-
Aug 25: Version v2026-08-25 released. It added 3DS2 payment authentication, split payments and payment schedules, grocery support (store locations, hours, fractional quantities), and independent versioning per capability. It also included breaking changes to the fulfillment schema, buyer consent and signing keys (UCP release notes).
-
Aug 28: Shopify storefronts began advertising v2026-08-25 in their discovery profiles, with no merchant action required (shopify.dev changelog).
-
Sep 2: A Payments Technical Council formed, with Adyen, Google, PayPal, Shopify, Stripe and others.
-
Around Sep 18–22: Google began enrolling eligible US Shopify merchants in native checkout inside AI Mode and Gemini through UCP, on by default, as reported on September 22 (Search Engine Land).
-
Sep 25 and Oct 6: A Lodging booking draft and a new
ask capability (agents ask a business free-form questions about returns, shipping or fit) were merged as drafts.
Why it matters for Shopify. Shopify co-governs UCP and implements it in its own agent endpoints. Google AI Mode, Gemini and Copilot checkout run on it. If you only learn one of these protocols, learn this one.
ACP (Agentic Commerce Protocol)
What it is. ACP is an open spec from OpenAI and Stripe, launched alongside ChatGPT Instant Checkout on September 29, 2025. It defines checkout sessions and delegated payment through Stripe's Shared Payment Token. The April 2026 release added a cart API, a push-style product feed, native orders, 3DS authentication and an MCP binding (ACP changelog). Meta joined ACP's technical steering committee on April 24, 2026, and is now listed as a lead maintainer.
What changed August to October 2026: Nothing was released. The newest dated version is still 2026-04-17, the last commit to the main branch was July 17, 2026, and a breaking change to the order schema is waiting in the unreleased changelog.
Why it matters less for Shopify checkout today. On March 24, 2026, OpenAI said the first version of Instant Checkout "did not offer the flexibility" it wanted and shifted ChatGPT's focus to product discovery, with merchants using their own checkout (OpenAI). Shopify's Help Center now describes ChatGPT as mainly a referrer: the shopper pays on your checkout inside ChatGPT's in-app browser.
So be careful with older articles that say Shopify stores sell inside ChatGPT through ACP Instant Checkout. That is no longer how it works for Shopify merchants.
WebMCP
What it is. WebMCP is a browser API that lets a web page register JavaScript tools, through document.modelContext.registerTool(), which AI agents running in the browser can call. Instead of guessing at buttons and forms, the agent calls a named tool such as "add to cart." It is a W3C Community Group draft edited by engineers from Microsoft and Google, and it is not on the W3C standards track (WebMCP spec).
Where it runs. Origin trials in Chrome 149 and Edge 150, support in ChatGPT Desktop, and experimental support in Brave Leo. Firefox and Safari have not shipped it (implementation status).
What changed August to October 2026:
-
Aug 5: Shopify switched on WebMCP tools for every Liquid storefront and the Hydrogen developer preview, with nothing to install. Tools include
search_catalog, get_product, show_variant, update_cart and proceed_to_checkout (shopify.dev changelog).
-
Aug 14: An
executeTool() method was added to the spec.
-
Sep 3: A "consequential action" hint was added so a page's tools can mark risky actions.
-
Sep 28: Shopify extended WebMCP to checkout. Agents can set addresses and delivery, apply discount codes and select a saved Shop Pay card. They cannot enter new card details, and the buyer must confirm before the order is placed (shopify.dev changelog, Checkout WebMCP docs).
-
Oct 8: The declarative API, which annotated HTML forms, was removed from the spec. Only imperative JavaScript tools remain. Guides telling you to annotate forms for WebMCP are now out of date.
Why it matters for Shopify. Standard Liquid themes get WebMCP for free. Custom experiences do not. A subscription selector, bundle builder, quiz or configurator needs custom registerTool code in your theme, or agents will fall back to guessing at the page.
MCP (Model Context Protocol)
What it is. MCP is an open protocol for connecting AI applications to external tools and data. Anthropic created it and donated it in December 2025 to the Agentic AI Foundation, a directed fund under the Linux Foundation co-founded by Anthropic, Block and OpenAI (Anthropic).
Current version. The 2026-07-28 specification redesigned MCP to be stateless, retired session IDs, added multi round-trip requests, and hardened authorization (MCP blog).
What changed August to October 2026:
-
Aug 22: A new roadmap focused on agent identity and enterprise security, unified HTTP transport, and progressive tool discovery (MCP roadmap).
-
Sep 11: The Skills extension was finalized.
-
Oct 6: MCP Server Cards were finalized, giving servers a standard
.well-known discovery file.
- No new spec version was published in this window.
Shopify's MCP servers today. "Shopify MCP" now mostly means UCP carried over MCP:
| Server |
Endpoint |
What it does |
| Storefront Catalog, Cart, Checkout and Order MCP |
https://{shop}/api/ucp/mcp |
Search, cart, checkout and order tools for one store. Requires an agent profile. Checkout completion is limited to trusted agents |
| Global Catalog MCP |
https://catalog.shopify.com/api/ucp/mcp |
Search across all Shopify merchants |
| Legacy Storefront MCP |
https://{shop}/api/mcp |
Catalog and cart tools removed. Only policy and FAQ search remains |
| Customer Accounts MCP |
Store custom domain |
Signed-in customer tasks like order status, with OAuth 2.0 and PKCE |
| Dev MCP |
Runs locally |
Connects coding assistants to Shopify docs and schemas |
Deadline to note: Shopify's Global Catalog REST API stops serving traffic on November 2, 2026. Anything built on it must move to Global Catalog MCP (shopify.dev changelog).
How the protocols fit together
They are mostly layers, not rivals:
-
Payment rails (Google's AP2, Visa Intelligent Commerce, Mastercard Agent Pay) handle authorization and agent identity.
-
Commerce languages (UCP or ACP) define what a product, cart, checkout and order look like.
-
Transport (MCP, REST or A2A) carries those messages between agents and businesses.
-
Browser tools (WebMCP) let an agent act inside a live page.
The real competition is between UCP and ACP, which cover the same commerce layer. Meta, Stripe and Salesforce participate in both. The Agentic AI Foundation put it plainly in an October 6 post: no single protocol completes the journey (AAIF).
Which AI surfaces use which protocol
| AI surface |
How Shopify products get there |
How the shopper buys |
| Google AI Mode and Gemini |
Google Merchant Center |
Native checkout via UCP |
| Microsoft Copilot |
Shopify Catalog |
Direct checkout, powered by UCP per Shopify |
| Meta Muse |
Shopify Catalog |
Shopify-powered direct checkout (Shopify has not said publicly whether this runs on UCP or ACP) |
| ChatGPT |
Shopify Catalog |
Referral to your checkout in an in-app browser |
| In-browser agents (Chrome, Edge, ChatGPT Desktop) |
Your live storefront |
WebMCP tools, with buyer confirmation |
What Shopify gives you automatically vs. what needs custom development
Automatic for eligible stores selling to US buyers:
- Shopify Catalog listing and distribution to AI channels
- UCP discovery profile and agent endpoints
- Direct checkout in Google, Copilot and Meta (on by default)
- WebMCP tools on Liquid storefronts and checkout
Needs custom work, especially on Shopify Plus:
-
Custom WebMCP tools for subscription selectors, bundle builders, product quizzes and configurators
-
Headless stores not built on Hydrogen. Shopify's WebMCP rollout covers Liquid storefronts and the Hydrogen developer preview, so plan to add tools yourself
-
Migrating custom agents or chatbots built on the old Storefront MCP tools to
/api/ucp/mcp with an agent profile
-
Moving off the Global Catalog REST API before November 2, 2026
-
Auditing what breaks in direct checkout: bundles, subscriptions, checkout extensibility blocks, client-side pixels
-
Catalog data quality: taxonomy categories, metafields, GTINs and policies, which decide whether agents pick you at all
The pattern is clear. Shopify switches the protocols on for you. The work that separates brands is data quality and the custom parts of your store that no protocol can describe on its own.
A decision guide for Shopify Plus teams
-
Running a standard Liquid theme with simple products? You are already on UCP and WebMCP. Spend your time on catalog data and Agentic Storefronts settings.
-
Selling subscriptions or bundles? Add one-time purchase options for agent checkout, and budget for custom WebMCP tools on your product pages.
-
Running headless on a custom front end? Shopify's automatic WebMCP rollout names only Liquid and the Hydrogen developer preview. Plan for WebMCP tools yourself and confirm your UCP profile.
-
Built a shopping assistant in 2025? Check whether it calls
/api/mcp catalog or cart tools. Those were removed.
-
Using the Global Catalog REST API? Migrate before November 2, 2026.
Frequently asked questions
What is the difference between UCP and ACP?
Both define how AI agents handle catalog, cart and checkout. UCP is backed by Google and Shopify and powers native checkout in Google AI Mode, Gemini and Copilot for Shopify stores. ACP is backed by OpenAI and Stripe, with Meta as a maintainer, and has shifted toward product feeds and discovery in ChatGPT.
Is WebMCP the same as MCP?
No. MCP connects AI applications to tools and data on servers. WebMCP is a browser API that lets a web page expose tools to AI agents running in the browser. The WebMCP spec references MCP, but it is a separate draft standard.
Does Shopify support UCP?
Yes. Shopify co-developed UCP, sits on its Governing Council, and storefronts advertise version v2026-08-25 in their /.well-known/ucp profile with no merchant setup.
Does my Shopify store need to implement ACP?
Not for selling in ChatGPT today. Shopify product data reaches ChatGPT through Shopify Catalog, and buyers complete purchases on your own checkout.
Is WebMCP live on Shopify stores?
Yes. Shopify enabled WebMCP tools on every Liquid storefront on August 5, 2026, and on checkout on September 28, 2026. Agents need a browser running the WebMCP origin trial, and buyers must confirm before an order is placed.
What happened to Shopify Storefront MCP?
Its catalog and cart tools were removed after deprecation windows that ended in June and August 2026. Agent tools now live at /api/ucp/mcp and require an agent profile. Only the policy and FAQ search tool remains on the old endpoint.
Which protocol should a Shopify Plus brand prioritize?
UCP, because it powers checkout in Google, Gemini and Copilot and Shopify implements it natively. After that, custom WebMCP tools for any product page logic that standard tools cannot describe.
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