ACP vs UCP vs AP2: a merchant's guide

ACP and UCP are the two open standards AI assistants use to sell products, and AP2 is the payment layer underneath one of them. The names sound interchangeable. They are not, and their status has changed fast in 2026. This guide compares them for a merchant: who backs each, what each one does, where it is live as of October 15, 2026, and what your store has to do, whether you sell on Shopify, WooCommerce, BigCommerce or your own stack.

For the bigger picture of AI agents that shop and buy, start with our guide to agentic commerce.

What is the difference between ACP and UCP?

ACP comes from OpenAI and Stripe and powers product discovery in ChatGPT, with checkout on your own site. UCP comes from Google with partners including Shopify and covers catalog, cart, checkout and orders, with checkout live in AI Mode and Gemini. Both are open standards, and you stay the seller.

Here is how they compare on the points a merchant cares about:

	ACP	UCP	AP2
Started by	OpenAI and Stripe, September 29, 2025	Google, January 11, 2026	Google, September 16, 2025
Maintained by	OpenAI, Stripe and Meta	A tech council with members from Google, Shopify, Etsy, Wayfair, Target, Amazon, Meta, Microsoft, Salesforce and Stripe	Contributed to the FIDO Alliance on April 28, 2026, for development in its working groups
Current version	2026-04-17	2026-08-25	v0.2
What it covers	Product feed, cart, checkout, delegated payment	Catalog, cart, checkout, identity linking, orders	Signed proof of what the shopper approved
Where you see it	ChatGPT shopping (US), discovery only	Google AI Mode and Gemini checkout	Inside payment flows, not a shopping surface

The biggest practical difference today is checkout. OpenAI moved away from a standalone Instant Checkout in ChatGPT, and purchases now finish on merchant-owned sites or apps. Google’s UCP checkout keeps the purchase inside AI Mode or Gemini, with the retailer as seller of record.

Both standards are open source under Apache 2.0. What you pay to sell through them depends on your payment provider and platform, as with any other sale.

What is Google UCP?

UCP, the Universal Commerce Protocol, is an open standard Google announced on January 11, 2026, co-developed with Shopify, Etsy, Wayfair, Target and Walmart. It lets AI agents search a store’s catalog, build a cart, check out and manage orders. Google uses it for checkout in AI Mode and Gemini.

Google announced UCP at the NRF show with endorsements from payment and retail companies, including Adyen, American Express, Mastercard, Stripe and Visa. Google said it works with Agent2Agent, AP2 and MCP, and that retailers “remain the seller of record.”

The UCP site lists five capabilities: catalog search and lookup, cart building, identity linking, checkout and order management. A store publishes a profile at /.well-known/ucp that tells agents what it supports. The specification runs over REST, MCP, Agent2Agent or an embedded checkout, and its current release is dated August 25, 2026.

Google’s own UCP checkout is already live for many sellers and still growing. In September 2026, Google said UCP enables direct checkout for hundreds of thousands of brands and retailers, and that new features in its Merchant Center integration hub, such as cart transfer to a merchant site, were gradually rolling out in the US, with Australia and Canada to follow early next year.

What is MCP and ACP?

MCP, the Model Context Protocol, is a general standard for connecting AI applications to tools and data. ACP, the Agentic Commerce Protocol, is a commerce standard from OpenAI and Stripe for product feeds, carts, checkout and payment between AI agents and businesses. They work at different layers.

OpenAI launched ACP on September 29, 2025, co-developed with Stripe, alongside Instant Checkout in ChatGPT. The ACP site says it is open source and community-designed under the Apache 2.0 license. The project repository now lists Meta beside OpenAI and Stripe as a lead maintainer.

ACP’s role then shifted. On March 24, 2026, OpenAI said the first version of Instant Checkout did not offer the flexibility it wanted, and expanded ACP to support product discovery. The April 2026 version added a feed API, so merchants can push catalog data to agents.

MCP sits one layer down. It connects an assistant to tools and data of any kind, and UCP can use it as a transport. Our guide to AI shopping agents covers MCP and Agent2Agent in more detail.

How does AP2 fit with UCP and ACP?

AP2, the Agent Payments Protocol, proves what a shopper approved when an agent pays, with signed mandates for the request and the exact cart. UCP supports AP2 as its payment trust layer. Google donated AP2 to the FIDO Alliance in April 2026. Merchants typically get it through their payment provider.

Google Cloud announced AP2 on September 16, 2025, with more than 60 organizations, among them Adyen, American Express, Mastercard and PayPal. At launch, AP2 described an Intent Mandate for what the shopper asked for and a Cart Mandate for the exact items and price they approved, signed with verifiable credentials. The current version names a Checkout Mandate for the items and a Payment Mandate for the payment, each first signed with the shopper’s limits and then for the final purchase.

On April 28, 2026, Google said it was transferring AP2 to the FIDO Alliance, an industry standards group. Version 0.2 added payments where the shopper is not present at the moment of purchase.

The card networks run their own programs for agent payments. Mastercard announced Agent Pay in April 2025. Visa announced Visa Intelligent Commerce the same month and a Trusted Agent Protocol in October 2025. For a merchant, all of this sits in the payment layer. Your payment provider decides which of these it supports.

One AI purchase, and which protocol handles each step

1. 1 The shopper asks

   A shopper asks ChatGPT, Gemini or Google AI Mode for a product. The assistant needs your catalog data to answer.

2. 2 Discovery

   ChatGPT reads product feeds sent through ACP, or catalogs already integrated through Shopify and Etsy. Google reads your Merchant Center feeds. UCP adds catalog search for agents that query your store directly.

3. 3 Cart and checkout

   In Google AI Mode and Gemini, UCP checkout keeps the purchase in the conversation, with you as seller of record. In ChatGPT, the shopper now finishes on your own site or app.

4. 4 Payment

   The payment goes through your payment provider. AP2 mandates can prove what the shopper approved, and providers such as Stripe and PayPal handle the delegated payment step.

5. 5 Order

   UCP includes order management, so the agent can follow the order after purchase. Fulfillment, returns and customer service stay with you.

Is ChatGPT Instant Checkout still available?

Not as a standalone feature. In March 2026 OpenAI let merchants use their own checkout while it focused on product discovery. Shoppers now discover products in ChatGPT and complete the purchase on the merchant’s own website or app. ChatGPT shopping is live for users in the US.

OpenAI’s merchant page puts it plainly: “We’re moving away from a standalone Instant Checkout experience in ChatGPT.” It adds that purchases “are completed on merchant-owned websites or apps,” and that there are no fees on purchases that start in ChatGPT.

For a merchant, ChatGPT is now a discovery channel. Your product data decides whether you are in the answer. The sale itself happens where it always has, on your site. Shopify’s help center describes ChatGPT the same way, as a discovery-focused referrer, while Google, Microsoft Copilot and Meta get checkout inside the channel.

That makes the question “will ChatGPT recommend my products?” more important than “can ChatGPT check out my products?” Our guide to ChatGPT recommendations covers what shapes the answer.

We built SourceVision to measure that answer. We ask ChatGPT, Gemini and Perplexity the questions your shoppers ask, many times over, and report how often your products appear, with the range across runs. Then we draft what each product page is missing from facts you confirm, and nothing is written without your approval. See how it works.

SourceVision is in an invite-only beta.

Request an invite

What do merchants need to do for ACP and UCP?

Most merchants do not implement either protocol themselves. Shopify and Etsy catalogs already reach ChatGPT, and Shopify storefronts support UCP. On other platforms, the route runs through Google Merchant Center, your payment provider or your platform’s agentic commerce program. Your product data is the part you control everywhere.

What to do depends on where you sell:

• Shopify. OpenAI says Shopify catalogs are already integrated into ChatGPT, with no additional work. Agentic storefronts are active by default for eligible stores, and Shopify storefronts support UCP version 2026-08-25. Google checkout through Shopify requires a US-based store.
• WooCommerce. WooCommerce was a launch partner for Stripe’s Agentic Commerce Suite. Its agentic commerce page lists both UCP and ACP as coming soon.
• BigCommerce. The BigCommerce platform serves UCP, and Catalyst storefronts pass its endpoints through on the store’s own domain as of version 1.12.0, released September 16, 2026.
• Any platform with Stripe or PayPal. Stripe’s Agentic Commerce Suite lets businesses sell across AI agents with a single integration. PayPal’s Agent Ready program supports ACP for ChatGPT and UCP for AI Mode and Gemini for Braintree merchants.
• Your own stack. For ChatGPT, apply to share a product feed with OpenAI. The merchant page says applicants join a waitlist. For Google, the Merchant Center help lists three steps: meet the requirements, submit the interest form, and complete the technical integration.

Three questions tell you where you stand today:

1. Is your catalog in Google Merchant Center and current? Prices, availability and policies there feed AI Mode and Gemini.
2. Does your platform list agentic channels or UCP support? Check its admin or changelog before you build anything yourself.
3. Does your payment provider support ACP or UCP? If it does, the payment side may already be handled.

Whatever the route, the protocols carry your product data. They do not improve it. Complete titles, descriptions, prices, availability and policies are what an assistant has to work with when it decides what to show.