Agentic Commerce Protocol Compared: ACP, UCP, AP2 and MCP

There is no single agentic commerce protocol. There are several, and they do different jobs. ACP, UCP and AP2 define how an AI agent shops and pays at a store. MCP (Model Context Protocol) is a more general standard that connects AI assistants to tools and data, and it is not specific to commerce. Most of these are designed to work together rather than replace each other.

This guide explains each one in plain terms, shows how they differ, and flags what is live today versus announced. For the broader concept, see our article Agentic Commerce Explained: How It Works for Online Stores.

What is the difference between ACP, UCP, AP2 and MCP?

Think of them as layers in one trip:

• MCP is the plug. It lets an AI assistant call tools and read data.
• ACP (Agentic Commerce Protocol) covers cart, checkout and delegated payment, from OpenAI and Stripe.
• UCP (Universal Commerce Protocol) covers the wider shopping journey: discovery, checkout and post-purchase, from Google with Shopify.
• AP2 (Agent Payments Protocol) is Google's payment authorization and trust layer, built around signed "mandates" (records that show a user approved a purchase).

A protocol here is simply an agreed format. If a store and an AI agent both speak it, they can do business without custom integration for every pair.

Comparison table: agentic commerce protocols side by side

Protocol	Led by	Main job	Commerce-specific	Status notes
MCP	Anthropic (now under the Agentic AI Foundation)	Connect AI assistants to tools and data	No	Widely adopted; current spec version 2026-07-28
ACP	OpenAI and Stripe	Cart, checkout, delegated payment, orders	Yes	Beta, date-based versions; ChatGPT Instant Checkout ended in March 2026
UCP	Google with Shopify	Discovery, checkout, post-purchase	Yes	Announced January 2026; phased rollout in Google surfaces
AP2	Google	Payment authorization and trust	Yes (payments only)	UCP is described as compatible with it

How is an agentic commerce protocol different from MCP?

The short version: MCP moves information and actions between an assistant and a tool. It does not know what a cart or an order is. A commerce protocol defines those things.

Anthropic introduced MCP in November 2024 as an open standard. In December 2025 it was donated to the Agentic AI Foundation, a fund under the Linux Foundation co-founded by Anthropic, Block and OpenAI. An MCP server exposes tools, resources and prompts, and an MCP client (an AI app) connects to it.

In practice, an MCP server can be the doorway through which a commerce protocol is offered. Google says UCP exchanges can run over an API, MCP or A2A (Agent2Agent, another Google protocol for agents talking to agents). ACP has also reportedly added MCP compatibility. So "agentic commerce protocol vs MCP" is not an either-or choice. If you want the basics of MCP first, read What Is MCP? A Plain-English Guide for E-commerce Merchants.

What is ACP, the Agentic Commerce Protocol?

ACP was released on 29 September 2025 by OpenAI and Stripe under the Apache 2.0 open-source license. It launched alongside Instant Checkout in ChatGPT.

How it works, according to the reporting:

• The agent never sees raw card details. A payment token is passed to the merchant.
• The merchant stays merchant of record (the party legally selling the goods) and can process payment through Stripe or another provider.
• The spec covers cart construction, capability negotiation, delegated payment and the order lifecycle.
• Changes are managed through a proposal process called SEP (Specification Enhancement Proposal).

What changed: Reports say OpenAI ended Instant Checkout in ChatGPT in March 2026. The exact date varies by source. OpenAI's stated reason was that the first version lacked flexibility. ACP continues, with more emphasis on product feeds and discovery, and shoppers are handed off to the merchant's own checkout or to merchant apps in ChatGPT. Reports also say few Shopify merchants went live. Treat adoption numbers as unconfirmed and check OpenAI's and Stripe's documentation for current status.

What is the Universal Commerce Protocol (UCP)?

UCP is an open protocol under Apache 2.0, announced by Google in January 2026 together with Shopify. Google's developer blog says it was developed with Shopify, Etsy, Wayfair, Target and Walmart, and endorsed by more than 20 other companies, including payment firms such as Adyen, Mastercard, Stripe and Visa.

What it covers:

• Discovery of products and merchant capabilities
• Capability negotiation (agent and store agree on what each supports)
• Checkout
• Post-purchase steps

Merchants keep merchant-of-record status. Agents reportedly find a store's capabilities in a manifest file at /.well-known/ucp, and payment handlers are negotiated per transaction. An optional embedded checkout exists for approved merchants.

What exists today: Google's implementation shows a "Buy" button on eligible listings in AI Mode in Search and in Gemini, paid with Google Pay and Google Wallet. Rollout is phased with an early access program, and only products with the native_commerce checkout-eligibility attribute show the button. Google's developer page lists AI Mode and Gemini on the web as live and the Gemini app as coming soon. Check Google Merchant Center Help for current eligibility.

What is the AP2 protocol?

AP2 (Agent Payments Protocol) is Google's answer to a narrow question: how does a payment provider know that a real person authorized what an agent is about to buy? It relies on signed mandates, which are verifiable records of what the user approved.

AP2 is not a shopping protocol. It does not handle product discovery or carts. It sits underneath, at the payment step. Google describes UCP as compatible with AP2 for secure agentic payments. The research behind this article did not confirm AP2 adoption by specific merchants or processors, so check the official AP2 documentation before planning around it.

UCP vs ACP: which one matters for my store?

Both let an agent buy from a store without a custom integration. The practical differences:

• Who pushes them: ACP is tied to OpenAI and Stripe, so ChatGPT is its main surface. UCP is tied to Google and Shopify, so AI Mode in Search and Gemini are its main surfaces.
• Scope: UCP is positioned as the full journey. ACP is centered on cart, checkout, payment and, more recently, feeds and discovery.
• Overlap: Both keep the merchant as merchant of record, both are open source, and both can be exposed through MCP.

For most merchants the choice is made by the platform. Shopify merchants are most likely to get UCP support through Shopify itself. Stripe users may get ACP support through Stripe's tooling. Neither choice is exclusive, and nothing in the notes suggests you must pick one.

What should a merchant do now?

1. Clean your product data. Every one of these protocols depends on accurate titles, prices, stock, shipping and return information.
2. Check your platform's status. Look at your e-commerce platform and payment provider documentation to see which protocols they support and whether you are eligible.
3. Check Google Merchant Center. Look for the early access program and the native_commerce attribute if you sell through Google surfaces.
4. Keep your own checkout solid. With ACP now steering shoppers to merchant checkouts, your checkout still matters.
5. Start MCP read-only. If you connect an assistant to your store or ad accounts, begin with read-only access. Our MCP Security checklist covers this in more detail.

What are the risks and limits?

• Fast-moving specs. ACP uses date-based versions and is in beta. MCP released a new spec in July 2026. Details change.
• Features come and go. Instant Checkout in ChatGPT shows that a launched feature can be withdrawn.
• Unclear conversion data. One report claims a large retailer saw weaker conversion from ChatGPT checkout than from its own site. It is a single secondary report, so do not treat it as a benchmark.
• Protocols do not create demand. Supporting a protocol makes your store reachable by agents. It does not make agents recommend you.
• Payments need trust controls. Letting an agent pay raises fraud, refund and dispute questions. Keep human approval in the loop until you understand how your provider handles them.

Verify every claim here against the official specifications before making technical or contractual decisions.