How Google's Universal Commerce Protocol (UCP) Works: A Payments Perspective

The NxN Problem

UCP attempts to address the NxN problem between AI platforms and Sellers. Imagine the average e-commerce merchant that wants to maximize it’s reach through all major AI platforms: Gemini, ChatGPT, Claude, Perplexity, etc. They’d have to build an integration with each platform, in every platform’s own defined protocol.

UCP makes this task less complex by providing a universal “language” with which the platforms and sellers can communicate. Let’s review how UCP achieves this with an end-to-end product discovery to checkout and payment through a simplified breakdown of steps.

Part 1: Capability Negotiation

Before anything can happen, both the AI Surface/Interface (Platform) and the Business (Merchant) define their UCP Profiles. The profile outlines what the platform or business is capable of doing under UCP and the relevant communication details.

1. The Platform looks up the Business’s profile from the UCP-structured URL address hosted by the business.

2. Platform contacts Business via endpoints listed in the Business’s profile, and sends over its own UCP profile.

3. Business computes the intersection of capabilities and services supported on both profiles and responds to the Platform with the details of what they both support.

4. Going forward, Platform can interact with Business within the selected UCP Services and Capability specifications.

Part 2: Product Discovery

1. Platform looks up or searches for products at the Business using lookup requests to the Business. How these inquiries are structured and handled is defined in the Catalog Capability.

2. Business responds with various details of products it has determined match the Platform’s lookup criteria, including product IDs, SKUs, prices, links, etc.

3. Platform can show the user the product details and interact with the user if they’d like to purchase the product(s).

Part 3: Checkout Initiation & Payment

If the user asks the Platform to purchase the product:

1. Platform makes checkout ‘creation’ request to the Business outlining the selected product IDs as line items and other checkout specific info like the user’s billing and shipping addresses. This request is defined in the Checkout Capability.

2. Business responds, acting on the requested checkout action with the created Checkout ID, supported payment handlers and its checkout specific configs and constraints.

3. Platform interacts with user to choose a payment method among those the Business indicated it supported in (2).

4. Platform triggers user payment authorization flow with the Credential Provider of the selected payment method. User authenticates and/or authorizes the payment with the Credential Provider (e.g. ApplePay, GooglePay, PayPal, ShopPay or other Tokenizer).

5. Credential Provider generates a payment token according to the Business’s payment handling configs shared in (2). The payment token is then given to the Platform.

6. Platform passes the Payment Token, the checkout ID and other checkout info in the “complete-checkout” request to the Business. This is the final step performed by the platform.

7. Business validates the checkout completion request and processes the provided payment token with its PSP.

8. The result of the payment processing and the order in general are returned to the Platform in the Business’s response. In case of issues that require escalation, such as SCA or 3DS, UCP has a requires_escalation state/response where the Business shares a continue_url to the Platform. With this URL, the platform can hand the user over to the Business through that URL either in a new browser tab or through an embedded web-view.

Part 4: Key Takeaways

1. Each Payment Method or its relevant authority, defines its UPC specs and how Businesses and Platforms use it under UCP.

2. By having a decoupled payment architecture, UCP solves for the N-times-N problem within agentic payments. Platforms do not necessarily have to build or integrate APIs and/or SDKs from every possible PSP a Business might have.

3. UCP is payment protocol agnostic. Although Google obviously promotes its own AP2 protocol, UCP also works with other payment protocols.

4. The business remains the merchant of record. The AI Platform does not take on the merchant of record responsibility.

5. Complex situations that require escalation such as 3DS, SCA or KYC can be handled for example, by handing the user over to the business through a web-view of whatever URL the business provides for escalation.

6. The AI platform defines how it recommends or searches for products. This is not defined by UCP. Remember, the platform communicates directly with the Business, UCP is just the shared communication language.

The Order, Identity Linking and Cart capabilities have not been mentioned in this overview but are worth checking out too. It is interesting that UCP only introduced the Catalog (lookup, search) capability in the April version release. The initial release at the end of 2025 didn’t have it, which to me it felt quite incomplete.

Let me know in the comments if you’ve found value in this article and video. Your feedback and critique is also very welcome.

See you in the next one - Paul