UCP vs ACP vs MPP: The Agentic Commerce Protocols Explained

The Universal Commerce Protocol (UCP) is an open standard, launched by Google with Shopify, Etsy, Wayfair, Target and Walmart in January 2026, that lets AI agents discover a store's capabilities, build carts, check out and track orders. The Agentic Commerce Protocol (ACP), whose lead maintainers are OpenAI, Stripe and Meta, covers similar ground and is the route for sharing product feeds with ChatGPT. The Machine Payments Protocol (MPP), from Stripe and Tempo, is different: it lets agents pay for APIs and digital services over HTTP, not buy physical products from a store. Most merchants will meet UCP through Google and ACP through ChatGPT, often both.

Everything below is dated November 2026. These specifications are versioned and changing; check the official pages before you build.

Protocol comparison table

The Universal Commerce Protocol in detail

UCP is designed so an agent can work with any compliant business without a custom integration. Its main building blocks:

• Capabilities such as checkout, with extensions such as discounts and fulfillment options.
• Catalog and cart: capabilities for catalog search and product lookup, and for building multi-item carts before checkout.
• Identity linking via OAuth 2.0, so logged-in shoppers keep loyalty or member pricing without sharing passwords.
• Orders: status, shipment tracking and returns via webhooks.
• Payments that separate the payment instrument (what the shopper pays with) from the payment handler (who processes it), using tokenized credentials.
• Discovery: businesses publish a JSON profile at /.well-known/ucp listing their services, capabilities, endpoints and payment handlers.

UCP supports REST and JSON-RPC transports and works with MCP, Agent2Agent (A2A) and AP2; with the AP2 extension, the agent platform submits signed checkout and payment mandates that the business and its payment processor verify. Under UCP the business stays the merchant of record and keeps its own business logic.

Google's implementation

Google's Merchant Center help describes UCP-powered checkout as a buy button on eligible product listings in AI Mode in Search and Gemini. Shoppers pay with Google Pay using details saved in Google Wallet. To take part, a merchant meets Google's UCP requirements, submits an interest form, completes the technical implementation, adds the native_commerce checkout eligibility attribute to products, sets up a Google Pay and Wallet Console account, and works with a PSP that integrates with the Google Pay API. Google describes access as phased through an early access program and says customers may see the experience soon, so treat it as an early program rather than a standard Merchant Center feature.

The Agentic Commerce Protocol in detail

ACP defines how an agent and a business complete a purchase. Stripe's documentation lists its building blocks as agentic checkout, cart and feed, delegated payment, delegated authentication (OAuth 2.0) and order webhooks. The full specification lives at agenticcommerce.dev and on GitHub, where the maintainers describe it as beta.

In ChatGPT, ACP matters in two ways:

• Product feeds. OpenAI's current feed spec takes full catalog snapshots, delivered at least daily over SFTP; Parquet is preferred, and gzipped JSONL, CSV and TSV are also accepted. Nine fields are required: item_id, title, description, url, brand, seller_name, image_url, availability and price. Separate flags control eligibility for search, checkout and ads. Direct feed onboarding is open to approved partners, who apply through OpenAI's form.
• Checkout. OpenAI's checkout spec keeps the merchant as merchant of record: ChatGPT calls the merchant's endpoints, and the merchant validates the order, calculates tax and shipping, charges payment through its own PSP and accepts or declines. In its most recent statement on the subject (March 24, 2026), OpenAI said the first version of Instant Checkout had not offered the flexibility it wanted, so it is letting merchants use their own checkout while it focuses on product discovery. Merchants that want deeper native experiences can build ChatGPT apps.

Stripe supports ACP payments through Shared Payment Tokens, which let an agent pass a scoped payment credential to the business without exposing card details.

The Machine Payments Protocol in detail

MPP solves a different problem. When an agent requests a paid resource, such as an API call or a dataset, the server replies with HTTP 402 and payment details. The agent authorizes payment, retries, and receives the resource plus a receipt. Stripe's integration supports cards through Shared Payment Tokens and stablecoin payments, settling into the business's Stripe balance. For a retail store, MPP is rarely the first priority. It matters if you sell digital goods, data or services that other software buys.

UCP vs ACP: practical differences for a merchant

• Where shoppers are: UCP is the route into Google's AI surfaces; ACP is the route into ChatGPT. Most merchants will want visibility in both.
• Scope: both cover checkout, identity and orders. UCP also defines catalog and cart capabilities and a discovery profile. ACP pairs with OpenAI's product feed format for discovery.
• Payments: Google's implementation uses Google Pay and Wallet. ACP is commonly paired with Stripe Shared Payment Tokens, though the spec supports other payment handlers.
• Merchant of record: in both, you stay the seller and keep control of order acceptance and fulfillment.
• Maturity: both are young. Expect version changes and phased access.

The protocols overlap more than they compete, and platforms are adding support for several at once. Adobe, for example, has stated that it is committed to supporting both UCP and ACP for Adobe Commerce; what you can use will depend on edition and licence.

What to do now

1. Fix product data first. Both routes depend on accurate titles, identifiers, prices, availability and images. This also helps classic search and marketplaces.
2. Get your Merchant Center account clean if you want to be ready for Google's UCP checkout when access opens to you.
3. Prepare a product feed for ChatGPT in OpenAI's format, or confirm your platform or feed tool can produce one.
4. Check your PSP's roadmap for Google Pay agent checkout and Shared Payment Tokens.
5. Make checkout API-ready. Tax, shipping and stock must be calculable via API for any agent checkout.
6. Avoid deep custom builds on a single spec version. Keep a thin adapter layer so protocol updates are cheap.

For the bigger picture of who does what in an agent purchase, read what agentic commerce is. For how agents connect to store tools, see MCP for ecommerce.

FAQ

Is UCP only for Google?

No. It is an open standard with many co-developers and endorsers. Google uses it for checkout in AI Mode and Gemini, and its co-developers include other retailers, platforms and payment companies, so other agents and platforms can use it too.

Do I need both UCP and ACP?

If you want to sell through both Google's and OpenAI's assistants, likely yes, or a platform that supports both. Start with product data and feeds, which serve both.

Is MPP a competitor to ACP?

Not really. They solve different problems, and Stripe documents both: ACP for agent checkout with businesses, MPP for agents paying for APIs and services.

Next step

Mistri helps Adobe Commerce and Magento merchants prepare feeds, APIs and protocol integrations; see our agentic commerce services.

Sources

UCP: Universal Commerce Protocol site; UCP on GitHub: announcements and releases; Google Developers Blog: Under the hood of UCP (January 11, 2026); Google Merchant Center Help: About UCP-powered checkout; Agentic Commerce Protocol on GitHub; OpenAI: Powering product discovery in ChatGPT (March 24, 2026); Stripe Docs: Agentic Commerce Protocol; Stripe Docs: Machine Payments Protocol; AP2: Agent Payments Protocol. Checked November 2026.