UCP Explained: The Universal Commerce Protocol

The Universal Commerce Protocol (UCP) is Google’s open standard for agentic commerce. Where ACP began as a checkout handshake, UCP is broader: it aims to standardize the entire shopping journey, from discovery and buying through to post-purchase support. It is the one genuine rival to ACP at the commerce layer, and it is live today inside Google’s own surfaces.

Who is behind it

UCP was announced on 11 January 2026 at the NRF retail show. It was co-developed with Shopify, Etsy, Wayfair, Target, and Walmart, and endorsed at launch by more than twenty other companies including Adyen, American Express, Best Buy, Flipkart, Macy’s, Mastercard, Stripe, The Home Depot, Visa, and Zalando. That circle has since widened: ucp.dev now lists Amazon, Microsoft, Meta, Salesforce, and Stripe alongside the original shopping co-developers, and the endorsement list has grown to include payment and platform names such as Affirm, Block, Checkout.com, Fiserv, Klarna, PayPal, SAP, Splitit, VTEX, and Worldpay. It is licensed under Apache 2.0, with the specification at ucp.dev and code under a dedicated GitHub organization.

How UCP is governed

Governance runs on two levels. A Governance Council is responsible for the overall adoption and health of the protocol. Beneath it sit per-domain Tech Councils, each responsible for the technical direction of one vertical. The public roster is the MAINTAINERS.md file in UCP’s GitHub organization, and it names individuals rather than companies, which is the detail most summaries miss.

The Shopping Tech Council reviews contribution proposals and stewards the shopping specification. Its founding members were Google, Shopify, Etsy, Target, and Wayfair. On 24 April 2026 it expanded to sixteen seats when Amazon, Meta, Microsoft, Salesforce, and Stripe joined, a notable convergence that brought several companies with previously rival positions under one open-standard governance body. All sixteen seats are currently filled, spread across ten companies. Four days later, on 28 April 2026, Stripe also joined the Governance Council alongside Google and Shopify, and that council added two more seats to be filled by election.

On 16 July 2026 a second domain body was seated. The Food Tech Council, which covers local food ordering and delivery, welcomed Block (Square), DoorDash, Google, Toast, and Uber Eats as inaugural members, filling ten of its sixteen seats with six left open for election. A third followed on 11 August 2026: the Lodging Tech Council, with inaugural members Amadeus, Booking.com, Expedia, Google, Hilton, Marriott, and Trip.com. Read the roster as a map of the lodging supply chain: global distribution and online travel agencies, hotel groups, and Google as the consumer surface convening the effort. Three domain councils in five weeks is the clearest signal yet that UCP intends to be a multi-vertical protocol rather than a retail one.

Two things are worth reading plainly off that roster. First, Google’s weight: it holds four of the sixteen Shopping seats and six of the ten filled Food seats, and one of the three filled Governance Council seats. UCP is open-governed on paper, and Google is still its largest single voice. Second, the overlap: Stripe and Meta sit formally inside UCP governance while remaining tied to the rival ACP, where Stripe is a founding maintainer and Meta is a lead maintainer. The big platforms are hedging across both commerce standards.

One distinction to keep straight: the companies listed on ucp.dev as shopping co-developers are a wider group than the Tech Council. Walmart, for instance, is named as a co-developer and as a launch retailer for Universal Cart, but does not hold a Tech Council seat.

Which version of the spec is current

UCP uses date-based releases. The published versions are v2026-01-11 (the launch release), v2026-01-23, v2026-04-08, and v2026-08-25, which is the current one. Releases and governance notices are posted on ucp.dev’s announcements page and tagged in the GitHub repository.

The 2026-04-08 release was a substantial expansion of scope: the Cart capability for basket building, Catalog search and lookup for product discovery, an updated Order capability, identity linking on an OAuth 2.0 foundation with capability-driven scopes, request and response signing, a first-class error model, and an embedded checkout protocol.

The 2026-08-25 release, published on 25 August 2026, is a change of shape rather than a change of scope. UCP’s announcement describes it as “major protocol enhancements, key structural refactorings to support multi-vertical expansion, payments security improvements (3DS2), structured request constraints, independent capability versioning, grocery shopping readiness and many more.” What that means in the published specification:

• The tree is no longer shopping-first. The top level is now Common, Shopping, and Payment. Payment constructs moved out of shopping and into the cross-vertical common group, so the 3DS challenge action, for example, is namespaced dev.ucp.common.payment.three_ds_challenge rather than living under shopping. This is the refactor that makes food and lodging possible without forking the payment layer.
• A Payment Authentication extension, with vendor-neutral EMV 3-D Secure challenge and device data collection actions, alongside new Payment Terms and Split Payments extensions and the existing AP2 Mandates extension.
• A Location capability under Common, for agents to find physical stores, which is the groundwork for grocery and for anything else with a store estate.

It carries breaking changes. If you have a UCP integration running, read the release notes against the capabilities you actually use before moving versions; UCP’s versioning policy lets you keep serving an earlier snapshot in the meantime.

What UCP actually does

What distinguishes UCP is scope. Its capability set covers catalog search and lookup, cart building, checkout, identity linking via OAuth 2.0, an order lifecycle (shipped, delivered, returned, refunded), and a payment-handler model. Businesses choose which capabilities to support. There are also two ways to do checkout: a native mode, where the platform negotiates directly with the seller’s checkout API and renders its own interface, and an embedded mode, where the seller’s own checkout interface is rendered inside the platform’s surface for more complex flows. In other words, UCP tries to standardize the whole sequence, with payment as one composable piece rather than something baked in.

That payment piece is where AP2 comes in. Google designed the two to fit together. UCP’s own documentation states that “UCP is fully compatible with Agent Payments Protocol (AP2)” and that AP2 “serves as the trust layer for agent-led transactions completed on behalf of a user.” Mechanically, AP2 is an opt-in UCP extension: the business declares support in its discovery document, signs the checkout state, and at completion the platform submits a CheckoutMandate and a PaymentMandate that the business and the payment processor verify separately. UCP is also designed to be compatible with the agent-to-agent protocol A2A and with MCP, and businesses can expose UCP capabilities over REST or JSON-RPC transports.

What is actually live

As of mid-2026, the specification, documentation, code samples, SDKs, reference implementations, and an interactive playground are published, and Google built the first production implementation to power checkout inside AI Mode in Search and the Gemini app for eligible US retailers, paying through Google Pay, with PayPal flagged at launch as a payment option to follow.

In March 2026 Google announced new optional UCP capabilities: a Cart option that lets agents add multiple items at once from a single store, a Catalog capability for retrieving real-time product details like variants, inventory, and pricing, and Identity Linking so shoppers keep loyalty and member benefits on UCP-integrated surfaces, plus a simplified onboarding path in Merchant Center. The same announcement named Commerce Inc, Salesforce, and Stripe as platforms that would implement UCP on their own products.

At Google Marketing Live on 20 May 2026, Google set out how far it intends to take this. Its Universal Cart, introduced the previous day at Google I/O, works across retailers and across Google surfaces, and UCP handles the checkout: shoppers either pay with Google Pay in a few taps or transfer the items to the merchant’s site to finish there, with the retailer remaining merchant of record either way. Google said shoppers would be able to try these checkout features “soon” with retailers including Nike, Sephora, Target, Ulta Beauty, Walmart, and Wayfair, and Shopify merchants such as Fenty and Steve Madden. Google also said UCP-powered buying would reach ad formats (Direct Offers and Shopping ads on YouTube), that Affirm and Klarna buy-now-pay-later options would be embedded in Google Pay, and that UCP-powered checkout would roll out across Canada and Australia in the coming months and later the UK.

Beyond retail, ucp.dev now lists two further verticals with their own co-developer groups: lodging (Amadeus, Booking.com, Expedia Group, Google, Hilton, Marriott, and Trip.com) and food (DoorDash, Google, Square, Toast, and Uber Eats). Detailed specifications for both are described as still to come.

Lodging is the furthest along on Google’s own side. Google runs a dedicated developer site, UCP for Lodging, pitching hotel operators on turning AI interactions into room bookings on Google surfaces such as AI Mode in Search, with the merchant of record staying with the hotel. What it does not yet offer is a specification: the page opens an interest waitlist and states that detailed onboarding and specs are coming soon, and the product image carries the label “Conceptual mock only.” That is a useful calibration for the whole vertical expansion. A developer surface and a waitlist are real steps, and they are still several steps short of something a hotel can integrate against. So UCP is real and shipping in Google’s own surfaces, is scoped to expand geographically and into new industries, and has a large endorsement list that now includes several payment providers and platforms. Broad third-party adoption outside Google’s surfaces is still early, and a good deal of what was announced in May is framed as coming rather than live.

A common point of confusion

“UCP” the acronym is overloaded in the wider tech world, and the generic phrase “unified commerce platform” is a different, older retail concept. In agentic commerce, UCP means this Google-led protocol. The live confusion to avoid is UCP versus ACP: two parallel standards launched by rivals, not two names for the same thing. For a side-by-side, see ACP vs UCP, and for where UCP sits among the other standards, see the protocol stack.

FAQ

What is UCP? Google’s open standard for agentic commerce, launched January 2026, covering the full shopping journey from discovery to post-purchase, with payment as a composable piece.

Is UCP the same as ACP? No. They are rival commerce-layer standards: UCP is Google’s whole-journey protocol; ACP is OpenAI and Stripe’s checkout protocol. Both are Apache 2.0, and several companies back both.

How do UCP and AP2 fit together? Google pairs them. UCP’s documentation says UCP is fully compatible with AP2 and that AP2 is the trust layer for agent-led transactions. AP2 is an opt-in extension within UCP: the business signs the checkout state, and at completion the platform submits a CheckoutMandate and a PaymentMandate for verification.

Which version of the UCP spec is current? UCP uses date-based releases. The published versions are v2026-01-11, v2026-01-23, v2026-04-08, and v2026-08-25, which is the current one. UCP describes the 25 August 2026 release as introducing major protocol enhancements, structural refactorings to support multi-vertical expansion, payments security improvements (3DS2), structured request constraints, independent capability versioning, and grocery shopping readiness. It carries breaking changes, so existing implementers should read the release notes before moving versions.