UCP changing

What it is

UCP is Google and Shopify’s protocol for agent-driven shopping, announced in January 2026 and co-developed with Etsy, Wayfair, Target and Walmart, with more than twenty endorsing partners including Adyen, American Express, Best Buy, Mastercard, Stripe and Visa. Google’s reference implementation powers checkout in AI Mode in Search and the Gemini app.

How it works

Three layers:

1. Shopping service: the core transaction primitives. Checkout session, line items, totals, messages, status.
2. Capabilities: independently versioned functional areas. Checkout, Orders, Catalog search and lookup, Cart building, and Identity Linking over OAuth 2.0. Each side advertises what it supports and validates the other’s claims.
3. Extensions: domain-specific schemas composed onto capabilities, with no central approval needed.

A merchant publishes a JSON manifest at /.well-known/ucp so an agent can discover its capabilities, endpoints and payment configuration. Payment instruments (what the buyer pays with) are separated from payment handlers (who processes it).

It is compatible with AP2 for purchase authorization and can be reached over plain APIs, A2A or MCP.

When to use it

You are a merchant and want to be buyable in Google’s assistants. For ChatGPT, the equivalent is the Agentic Commerce Protocol. Shopify merchants get UCP through the platform.

Watch out for

• Four commerce protocols exist in this space. The short version: x402 is the payment rail for machines, AP2 is user authorization, and ACP and UCP are merchant integration for ChatGPT and Google respectively.