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UCP and ACP, Explained for a Small Store (2026)

What Google's Universal Commerce Protocol and the Agentic Commerce Protocol from OpenAI and Stripe are, where each runs today, and what each asks of a merchant, from their own pages.

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Enes Özkan, Founder and CEO8 min read

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In this article
  1. What is UCP?
  2. What is ACP?
  3. What does each ask of a merchant?
  4. What can't be bought through Google's agent checkout?
  5. What should a small store do first?
  6. Where does FaStart stand?
  7. FAQ
  8. Sources

UCP and ACP are open standards that let an AI assistant shop with a store while the store stays the seller. Today they show up in different places: UCP runs checkout in Google's AI Mode and Gemini for select US merchants, starting from a Merchant Center account, while ChatGPT uses ACP mainly to read product feeds and sends shoppers to the store's own site to pay.

Note: Read on 20 October 2026 from Google's, OpenAI's, Stripe's and the protocol's own pages, all linked below. Both programs open to new countries and merchants in stages, so check the source before you plan around a detail.

What is UCP?

The Universal Commerce Protocol is an open standard Google launched on 11 January 2026. Google co-developed it with Shopify, Etsy, Wayfair, Target and Walmart, and more than 20 others endorsed it, including Adyen, American Express, Mastercard, Stripe and Visa. Google describes it as "a common language for agents and systems to operate together across consumer surfaces, businesses and payment providers," covering discovery, buying and support after the sale (Google).

On Google, UCP is what puts a buy option on product listings in AI Mode in Search and in the Gemini app. In March 2026 Google announced new optional capabilities: carts, live catalog details such as price and stock, and account linking so shoppers get their loyalty pricing (Google). Its Universal Cart, which uses UCP for checkout, opened in the US on 15 October 2026. Whether the shopper pays with Google Pay in the cart or moves it to the merchant's site, the merchant remains "the seller of record" (Google).

Who can use it right now is narrow. Google's Merchant Center guide, updated 19 October 2026, says the UCP integration hub "is gradually rolling out in the United States, with Australia and Canada to follow early next year," covers "only products sold within the United States," and that checkout "is available for select merchants" through an early access program (Google).

What is ACP?

The Agentic Commerce Protocol is an open standard, published under the Apache 2.0 license, that Stripe and OpenAI developed "to define a common language for how agents and businesses transact." The business stays the merchant of record, keeps the customer relationship, and "can then choose to accept or decline transactions on a per agent, per transaction, or custom logic basis." It works with any compatible payment provider, and Stripe's Shared Payment Token was the first (agenticcommerce.dev). Stripe's own documentation now names Meta as a third creator (Stripe).

ChatGPT is where most small stores will meet ACP, and its role there changed this year. On 24 March 2026 OpenAI wrote that "the initial version of Instant Checkout did not offer the level of flexibility that we aspire to provide, so we're allowing merchants to use their own checkout experiences while we focus our efforts on product discovery." Through ACP, merchants share product feeds and promotions so their catalogs show up in ChatGPT (OpenAI). ChatGPT's page for merchants says it sends shoppers "to your site or app by default, with no fees for purchases made on your site or app," and that shopping is live for ChatGPT users in the US (ChatGPT). Checkout inside ChatGPT still exists for approved partners (OpenAI).

What does each ask of a merchant?

UCP on GoogleACP in ChatGPT
Who can join todaySelect merchants in an early access program, for products sold in the US; you join a waitlist and Google approves the integration before it goes liveMerchants who apply and are accepted; Shopify and Etsy catalogs are already integrated
Product dataA Merchant Center account in good standing with approved products, and a feed that marks each product that may be bought on GoogleA product feed in OpenAI's format; OpenAI recommends the full feed once a day and updates through the day
PoliciesA return policy in Merchant Center with its cost, window and a link, plus customer support contact detailsOpenAI's prohibited products policy; you answer for your products and content
CheckoutEither native checkout, where you build the checkout endpoints Google calls, or a cart path that hands the cart to your site; plus a profile published at /.well-known/ucpBy default none: the shopper pays on your site. Approved Instant Checkout partners build five checkout endpoints
PaymentsYour payment provider must be able to process Google Pay tokensYour existing payment provider
After the saleOrder updates pushed to Google: created, shipped with tracking, deliveredOrder events sent by webhook, for checkout partners
Who is the sellerYou, as merchant of recordYou, as merchant of record
Cost to youNo fee mentioned on the UCP pages readNo fees for purchases made on your own site or app

The Google rows come from its UCP guides (overview, Merchant Center, FAQ, orders, profile). The ChatGPT rows come from OpenAI's feed guide, its checkout spec and the merchants page.

What can't be bought through Google's agent checkout?

The list is long. Google's Merchant Center guide lists products that must stay out of checkout, among them subscriptions and anything billed on a cycle, personalized goods such as engravings, pre-orders, refurbished, used and "Final Sale" items, products that need special or freight delivery, and age-restricted items. Google asks merchants to leave the checkout flag empty or false on those, so they can stay in the feed and in Google's listings without the buy button.

Take Bellamy Coffee, a roaster in Tacoma (an example, not a real shop). Its bags of beans can be marked eligible in its Merchant Center feed. Its monthly subscription can't, because Google keeps recurring billing out of checkout. On ACP's side, the protocol itself supports subscriptions, and if ChatGPT accepts Bellamy's feed, both would send the shopper to Bellamy's own site to pay.

What should a small store do first?

Start with the product data, because it's the one thing both programs read. That means a feed with accurate titles, prices, availability, GTINs and shipping, kept current. If your Merchant Center feed is complete and your returns and support details are filled in, you've done the part of Google's preparation that doesn't need a developer.

Then ask your platform what it already does before you build anything. OpenAI says that "If you sell through Shopify or Etsy, your catalog is already integrated, and no additional setup or application is required." Google tells merchants who use a platform or service provider to "contact them directly to learn about their UCP integration plans."

Write your return policy with a cost, a window and a link. Google requires all three for checkout and shows the policy on its checkout screen.

And decide which products you'd sell through an agent at all. Google's eligibility flag is set per product, and under ACP you can decline a transaction by agent, by order or by your own rule. Our guide to getting a store ready for AI shopping agents covers the rest of the groundwork, from crawlers to policies, and what an AI agent can run in your store today covers the jobs that should still wait for your yes.

Where does FaStart stand?

We plan a way for shoppers' AI assistants to read a FaStart store's catalog and buy within the store's own rules. The page on agentic commerce for merchants shows where that work stands and walks through the four things worth fixing in a store now, and a demonstration on sample products shows the kind of product record an assistant can read.

FAQ

Do I need both UCP and ACP? Only for the places you want to sell. UCP is how Google's AI surfaces check out, and ACP is how ChatGPT reads merchants' catalogs. A complete, current product feed is the shared starting point.

Will using UCP change my ranking on Google? Google says no: "Opting for our Native integration does not influence how we rank your offers in product listings."

Who owns the customer when an agent places the order? You do. Google says you "retain full ownership" of the customer relationships and data, and ACP keeps the business as merchant of record with its own customer relationship.

Sources

All read on 20 October 2026.

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