ACP vs UCP vs MCP vs AP2: Agentic Commerce Protocols Compared

ACP, UCP, AP2 and MCP are open protocols that handle different steps of a purchase made by an AI agent. ACP (OpenAI and Stripe) and UCP (Google, with a ten-member Tech Council) let a shopper’s agent read a merchant’s catalog and complete checkout. AP2 (now at the FIDO Alliance) proves the user authorized the payment, and MCP (now at the Linux Foundation) is the general way agents call tools, which ACP and UCP can both run over.

Visa’s Trusted Agent Protocol and Mastercard Agent Pay add agent trust and tokenized payment at the card networks. None of these protocols decides what a merchant should offer a particular customer. That is the gap a personalized offer fills, and it’s where haggl.ai works. New to the topic? Start with what agentic commerce is.

Updated 14 October 2026. This version replaces our February 2026 comparison and covers this year’s changes, from OpenAI’s move away from Instant Checkout to AP2’s move to the FIDO Alliance.

The protocols at a glance

ACP: product feeds and checkout for ChatGPT

OpenAI and Stripe published the Agentic Commerce Protocol in September 2025 under the Apache 2.0 license. It defines how an agent receives a merchant’s product feed, opens a checkout session and passes a payment token without exposing the card. Stripe’s Shared Payment Token was the first compatible method, and the merchant stays the merchant of record (agenticcommerce.dev). OpenAI and Stripe are the founding maintainers, and Meta took a seat on the technical steering committee in April 2026.

Two releases widened it this year. Version 2026-01-30 added capability negotiation, a payment handler framework and the first extension, for discount codes. Version 2026-04-17 added carts, a discovery file at /.well-known/acp.json, a feed API and an MCP binding for checkout. “Capability negotiation” here means the agent and the merchant agree which features they both support. It has nothing to do with price.

The bigger change was in ChatGPT. In March 2026, OpenAI said the first version of Instant Checkout wasn’t as flexible as it wanted, so merchants can now use their own checkout while ChatGPT concentrates on product discovery (CNBC). Merchants share product feeds and promotions with OpenAI, and retailers can still build their own apps inside ChatGPT. OpenAI’s docs say feed onboarding is open to approved partners.

UCP: Google’s standard for the whole shopping journey

Google launched the Universal Commerce Protocol in January 2026. It was co-developed with Shopify, Etsy, Wayfair, Target and Walmart, and endorsed by more than 20 companies, including Adyen, American Express, Mastercard, Stripe and Visa (Google for Developers). A business publishes a profile at /.well-known/ucp, and agents call its capabilities over REST, MCP or A2A. Payments are compatible with AP2. At launch, UCP was set to power checkout on eligible Google listings in AI Mode and the Gemini app, starting with US retailers (Google).

What changed in 2026:

• March: Cart, Catalog and Identity Linking, so agents can build multi-item carts, read live prices and stock, and carry a shopper’s loyalty benefits (Google).
• April: Amazon, Meta, Microsoft, Salesforce and Stripe joined Google, Shopify, Etsy, Target and Wayfair on the Tech Council that steers the standard.
• May: Google announced a Universal Cart across retailers and said UCP checkout would reach Canada and Australia, then the UK (Google).
• August: release v2026-08-25 formalized a loyalty extension and added payment schedules, split payments and grocery features.

UCP also carries offers the merchant has already set up. Its discount extension lets an agent submit codes and the business return the discounts it applied, including automatic ones. Talon.One sells UCP extensions that expose promotions and loyalty programs to agents.

AP2: proof that the user approved the payment

Google announced the Agent Payments Protocol in September 2025 with more than 60 organizations. AP2 uses cryptographically signed mandates: a record of what the user asked for, the exact cart they approved and the payment they authorized. Together they give merchants, payment providers and networks an audit trail when an agent, not a person, makes the purchase.

In April 2026, Google donated AP2 to the FIDO Alliance and released v0.2. It adds payments the agent makes while the user isn’t present, such as buying tickets the moment they go on sale. Google and Mastercard also built Verifiable Intent, an AP2-compatible record of what the user authorized, which is going to FIDO too.

MCP: how agents call tools

Anthropic created the Model Context Protocol and, in December 2025, donated it to the Agentic AI Foundation, a fund under the Linux Foundation co-founded by Anthropic, Block and OpenAI. ChatGPT, Cursor, Gemini, Microsoft Copilot and VS Code support it, as does Claude. The current specification is dated 2026-07-28.

MCP isn’t a commerce protocol. It’s the general way an AI app finds and calls tools, which is why “UCP vs MCP” isn’t a real choice: UCP defines what a cart or a checkout is, and MCP is one way to call it. ACP added an MCP binding with five checkout tools in April 2026, and UCP supports MCP alongside REST and A2A.

WebMCP brings the same idea to the browser: a page registers tools that an agent in the browser can call. It’s still experimental, offered as an origin trial in Chrome 149.

Visa and Mastercard: trust at the card networks

Visa launched the Trusted Agent Protocol with Cloudflare in October 2025. An agent signs its requests using HTTP Message Signatures, so a merchant can tell a legitimate agent acting for a user from an anonymous bot. The agent can also pass identifiers the consumer agreed to share, such as a loyalty number (GitHub). In April 2026, Visa began piloting Intelligent Commerce Connect, one integration that accepts agent payments made through the Trusted Agent Protocol, the Machine Payments Protocol, ACP and UCP.

Mastercard launched Agent Pay in April 2025. It issues Agentic Tokens to agents that are registered and verified, and the consumer controls what the agent may buy. Mastercard works with acquirers and checkout providers such as Braintree and Checkout.com, so the tokens arrive through the payment setup merchants already use. In June 2026 it added Agent Pay for Machines, for frequent, low-value payments made by agents.

Where a personalized offer fits

Feeds and catalogs tell the shopper’s agent what you sell. ACP and UCP complete the checkout. AP2, Visa and Mastercard prove the user approved the payment. MCP carries the calls. Each one moves something the merchant has already decided: a product, a price, a promotion, a code.

None of them defines how you decide what to offer one customer, or why. Yet that is what a shopper’s agent compares when it checks for something better before it buys (see how to sell to AI shopping agents). A public code gives everyone the same terms.

This is where haggl.ai works. Your sales agent talks with the shopper’s agent, asks what matters to that customer and makes a personalized offer: a discount, a bundle, a plan or a gift. Every offer stays inside the budget you cap and the max discount you set. You see what the shopper’s agent asked, what your sales agent offered and whether the shopper accepted. Negotiation is how it works, not what it is. The product is an offer made for that customer.

haggl.ai works next to the protocols, not instead of them:

• Discovery: the embed adds discovery tags to your storefront, and /.well-known/mcp.json describes the MCP server.
• The conversation: shoppers’ agents connect over REST (/api/negotiate), remote MCP (/api/mcp) or WebMCP tools where the browser supports them. All three share one session.
• Checkout: an accepted offer becomes a single-use Shopify discount applied to the cart, or a single-use Wix coupon with a checkout link. The shopper finishes your normal checkout.

Today this runs on Shopify Plus, with haggl.ai-assisted setup, and on Wix through the haggl.ai app for Wix (email contact@haggl.ai for the install link). Merchants can start at haggl.ai/ecom. Developers can read the full spec at /protocol.

How to choose

For merchants

1. Let your platform handle discovery and checkout. Shopify’s Agentic Storefronts are on by default for eligible stores and reach ChatGPT, Microsoft Copilot, Gemini and AI Mode, and Meta. Wix is rolling out Stripe’s Agentic Commerce Suite to eligible merchants. On your own stack, Stripe supports selling through agents with UCP or ACP.
2. Get your product data right. OpenAI and Google both start from it: a product feed for ChatGPT, and Merchant Center for Google.
3. Ask your payment provider about agent payments. AP2, Visa and Mastercard support mostly reaches merchants through the provider, not through code you write.
4. Decide what you’ll offer, and to whom. Discovery and checkout put you on the shortlist. The offer is what the shopper’s agent compares. Set a budget and a max discount before you start.

For developers

• Building a shopper’s agent: use MCP for tools, UCP and ACP for carts and checkout, AP2 for payment authorization, and the Trusted Agent Protocol so Visa merchants can verify you.
• Building for a merchant: publish /.well-known/ucp and /.well-known/acp.json if you implement those protocols, and expose your tools over MCP. To add personalized offers, read the haggl.ai protocol or install haggl.ai with a coding agent.

Frequently asked questions