Universal Commerce Protocol (UCP) Explained: What It Means for Merchants

What is the Universal Commerce Protocol (UCP)?

The Universal Commerce Protocol (UCP) is an open standard that defines how an AI agent finds out what a store sells, builds a cart, checks out and follows the order afterwards, without a custom integration for every agent. Google announced it on 11 January 2026 at the NRF retail show and co-developed it with Shopify, Etsy, Wayfair, Target and Walmart. The specification is open source under the Apache 2.0 licence, published at ucp.dev and in the Universal Commerce Protocol GitHub repository.

For a merchant, three facts matter more than the acronym:

• It is how Google sells your products inside AI answers. UCP powers checkout in AI Mode in Google Search and in Gemini, and since 15 October 2026 it also runs checkout in Google's Universal Cart in the US.
• You stay the seller of record. The order, the payment, the customer and the returns are yours, not Google's.
• Eligibility is narrow today. Google's own checkout is limited to US merchants and to products that suit a one-step purchase. Subscriptions, personalised goods and pre-orders, for example, are out.

The rest of this guide explains who backs the protocol, how a UCP checkout actually flows, what you need in place to be eligible, and what is still missing. For the bigger picture of AI shopping agents, start with what AI commerce is.

Who backs UCP, and who governs it

At launch Google listed five co-developers and more than 20 endorsers, including Adyen, American Express, Best Buy, Flipkart, Macy's, Mastercard, Stripe, The Home Depot, Visa and Zalando (Google, 11 January 2026).

The list grew in two steps:

• March 2026. Google said Commerce Inc, Salesforce and Stripe would implement UCP soon (Google, 19 March 2026).
• April 2026. A press release of 24 April announced that Amazon, Meta, Microsoft, Salesforce and Stripe joined the UCP Tech Council, the body that reviews proposals and maintains the protocol. The founding council members named in that release are Google, Shopify, Etsy, Target and Wayfair. Walmart, a launch co-developer, is not in that list.

As of October 2026, ucp.dev lists Amazon, Microsoft, Meta, Salesforce and Stripe among the shopping co-developers, plus separate groups for lodging (Booking.com, Expedia Group, Marriott and others) and food ordering (DoorDash, Uber Eats, Toast and others). The copyright line credits the UCP authors, and the site names no foundation.

Read the council list carefully. Membership means a company helps shape the standard. It does not mean that company's own store or assistant already accepts UCP checkouts. Check each surface on its own before you plan around it.

How a UCP checkout flows

UCP has three parties: the platform (the agent surface, such as AI Mode), the business (you), and the payment handler (the wallet or processor that supplies a payment credential). The protocol is split into capabilities, and a store supports only the ones it chooses. As of October 2026 the specification lists Catalog, Cart, Checkout, Identity Linking and Order for shopping.

A purchase through Google's checkout runs roughly like this, based on Google's developer walkthrough and the checkout specification:

1. Discovery. Your store publishes a JSON profile at the path /.well-known/ucp. It lists your services, the capabilities you support (checkout, discounts, fulfilment), your endpoints and your payment handlers. The agent reads it instead of relying on a hard-coded integration.
2. Create checkout. When the shopper shows intent to buy, the platform creates a checkout session on your server. You return the line items, totals, tax and delivery options.
3. Update. The platform sends the shipping address, the chosen delivery option or a discount code. You recalculate and return the new totals.
4. Escalate if needed. If something cannot be handled through the API, such as a delivery date picker or an age check, you set the status to requires_escalation and return a continue_url. The shopper finishes that step on your own pages.
5. Pay. The platform collects a payment instrument from a handler such as Google Pay. You receive a token, not the raw card number, and charge it through your existing processor.
6. Complete. The session moves from ready_for_complete to completed, and you place the order.
7. After the sale. With the Order capability, you push status, tracking and return updates back to the platform.

Two technical details matter for planning. First, transport: Google says the checkout capability can be bound to REST, MCP or A2A, so you are not tied to one style of API (Google Developers Blog). Second, autonomy: the specification says a checkout must be finalised by the user through a trusted interface unless the AP2 Mandates extension is supported. In plain terms, an agent cannot buy on its own without signed proof of what the shopper approved. That proof comes from Google's Agent Payments Protocol (AP2).

The protocol is versioned by date. The current checkout specification shows version 2026-08-25, and Shopify storefronts advertise that version in their discovery profiles since late August 2026.

Who is the seller of record?

The merchant. Google says it in each of its main UCP announcements:

• The January launch post says retailers remain the seller of record (Google).
• The developer guide says you remain the Merchant of Record, keep your customer data and relationships, and own the transaction and the post-purchase experience (Google for Developers).
• The Universal Cart announcement repeats it and adds that the merchant handles confirmations and customer support (Google, 15 October 2026).

In practice this means the AI surface is a storefront, not a marketplace. Your processor charges the card. You collect and remit sales tax, ship the order, take the returns and answer the chargebacks. Google shows your return policy on its checkout screen, pulled from Merchant Center, so whatever you publish there becomes part of the sale.

UCP does not turn Google into your store. It turns your store into something an agent can buy from.

Jakub Riegel

The upside is that you keep the customer record and the order data. The cost is that every promise in your feed is now a promise at checkout. A wrong price or a stale stock count no longer just loses a click. It produces a failed or refunded order inside someone else's interface.

What a merchant must do to be eligible today

There are three routes, depending on your stack.

If you sell on Shopify

Shopify co-developed UCP, and its Agentic Storefronts feature manages the AI channels from the Shopify admin (Shopify, 11 January 2026). As of October 2026, Shopify's help center says Agentic Storefronts is active by default for eligible stores. For Google AI Mode and Gemini it requires products to flow through the Google & YouTube sales channel or Merchant Center, and direct checkout turned on (Shopify Help Center). Shopify's own pages describe Google access as limited to US-based stores selling to US customers. We cover the Shopify side in detail in Shopify and agentic commerce.

If you integrate directly with Google

Google's Merchant Center preparation guide sets the bar:

• A Merchant Center account in good standing, with products approved for free listings.
• Return policies set in Merchant Center, each with the return cost, the return window and a link to the full policy.
• At least one customer support contact (website, email or phone). It powers the Contact Merchant link on the order confirmation.
• The product attribute native_commerce, with its sub-attribute checkout_eligibility set to TRUE, on every product you want sold through checkout. Missing or FALSE means not eligible, and that is the default.
• A consumer_notice on products that legally need a warning, such as California Proposition 65 items.
• A merchant_item_id when your feed ID differs from the product ID your checkout API uses.

Then you build the checkout itself. Google's default is native checkout, where your logic plugs straight into AI Mode and Gemini. An embedded, iframe-based checkout is reserved for specific merchants Google approves (Google for Developers). Onboarding runs through a waitlist and, since September 2026, through a UCP integration hub in Merchant Center (Google, 16 September 2026).

If you run another platform or a custom stack

Check whether your commerce platform or payment provider ships UCP before you build anything. Salesforce and Stripe announced support in March. As of October 2026, Stripe's agentic commerce documentation lists UCP next to its own tools. The protocol is the same whoever implements it, so a vendor implementation saves you the endpoint work but not the data work.

What is still limited

UCP the protocol and Google's checkout the product move at different speeds. As of October 2026:

• Geography. Google's checkout is US only. Google said Australia and Canada should follow early in 2027 (Google, 16 September 2026).
• Products. Google excludes subscriptions and instalment plans, personalised goods, used and final-sale items, pre-orders, bundled services, age-restricted items, rentals and most digital goods (Merchant Center guide).
• Features on Google's side. The protocol added Cart, Catalog and Identity Linking in March 2026 (Google). Google's developer guide still lists multi-item carts, loyalty account linking and post-purchase tracking and returns as roadmap items, and describes the Gemini app as coming soon. Google's February and October posts describe checkout in the Gemini app already. The documentation and the announcements do not agree here. Check your Merchant Center account rather than either one.
• Adoption figures. Google says UCP enables direct checkout for "hundreds of thousands of brands and retailers" (Google, 16 September 2026). That is Google's own number. We found no independent count and no published conversion data.
• Other assistants. ChatGPT and Microsoft Copilot run on a different standard, the Agentic Commerce Protocol. See ACP vs UCP vs AP2 for how they differ, and what happened to ChatGPT Instant Checkout for why in-chat checkout is not a given.

The timeline so far:

What to do now

1. Clean the feed first. Every agent surface starts from your product data, and UCP checkout reads your price, stock and policies at the moment of sale. Fix titles, attributes and variants before anything else. Our guide on product attributes and structured data covers the fields agents depend on.
2. Set your policies once, properly. Return cost, return window and a support contact are eligibility requirements, not nice-to-haves.
3. Choose your checkout scope. Set checkout_eligibility per product. Leave out anything that needs a conversation: made-to-order items, bundles with services, regulated goods.
4. Use your platform before you build. On Shopify, review Agentic Storefronts and the direct checkout setting. On other platforms, ask your vendor and payment provider for their UCP timeline.
5. Design the escalation path. Anything your API cannot settle goes back to your own pages through the continue_url. Make that page fast on mobile and make it pick up the cart where the agent left off.
6. Watch the version dates. UCP ships dated versions. Track the changelog in the GitHub repository and the status of the Gemini app, multi-item carts and new countries in your Merchant Center account.

More on the agent side of this shift lives on the AI shopping agents topic page.

FAQ

What is the Universal Commerce Protocol?

An open standard, announced by Google on 11 January 2026, that lets AI agents discover a store's products, build a cart, check out and track the order through one shared interface. Shopify, Etsy, Wayfair, Target and Walmart co-developed it.

Is UCP open source, and where is it on GitHub?

Yes. The specification is licensed under Apache 2.0 and lives in the Universal-Commerce-Protocol organisation on GitHub, with documentation and a playground at ucp.dev.

Who is the seller of record when a shopper buys through Google AI Mode?

The merchant. Google states that retailers remain the seller of record: you charge the payment, ship the order, handle returns and own the customer relationship.

Does Shopify support the Universal Commerce Protocol?

Yes. Shopify co-developed UCP, its storefronts publish a UCP profile, and eligible US stores can sell through Google AI Mode and Gemini via Agentic Storefronts with direct checkout turned on.

What is the difference between UCP and ACP?

Both move a checkout from an AI agent to the merchant. UCP comes from Google and its retail partners and runs Google's surfaces; ACP comes from OpenAI and Stripe and runs ChatGPT and Stripe-powered Copilot Checkout.