What is the difference between ACP and UCP?

ACP comes from OpenAI and Stripe and is mainly how catalogues reach ChatGPT product discovery. UCP comes from Google and partners and covers discovery and transaction on Google's AI surfaces through a profile at /.well-known/ucp.

Does ChatGPT still have Instant Checkout?

Not as the normal path. In March 2026 OpenAI moved away from checkout inside ChatGPT; purchases that start in ChatGPT now complete on the merchant's site, with no fees on them.

Who is the merchant of record in agentic commerce?

The store. It charges the payment through its own provider and handles tax, refunds and fulfilment. The agent never holds the card number.

Does Magento support ACP or UCP natively?

No. Magento needs modules or custom work for the product feed, the UCP profile and any agent endpoints.

Canonical definition

Agentic Commerce Protocols (ACP, UCP, AP2, MCP) – Definition

An agentic commerce protocol is a standard that lets an AI agent discover products, build a cart and help complete a purchase with a store – while the store stays the merchant of record. Four protocols matter in 2026: ACP (OpenAI and Stripe), UCP (Google and partners), AP2 for payment authorisation, and MCP as the tool-calling layer the others can run on.

In one sentence

Four standards, four jobs: ACP and UCP for discovery and buying, AP2 for payment proof, MCP as the plumbing.

The protocols, side by side

	ACP	UCP	AP2	MCP
Full name	Agentic Commerce Protocol	Universal Commerce Protocol	Agent Payments Protocol	Model Context Protocol
Led by	OpenAI and Stripe	Google with retail partners	Google, now at the FIDO Alliance	Anthropic, now at the Linux Foundation
Job	Product feed and discovery for ChatGPT; checkout model for agents	Discovery and transaction across Google’s AI surfaces	Proof that the shopper authorised a payment	Tool calling – the transport other protocols can use
Latest version	2026-04-17 (beta)	2026-08-25	v0.2	2026-07-28
Store publishes	A product feed sent to OpenAI	A profile at `/.well-known/ucp` plus endpoints	Usually nothing – payment providers implement it	An MCP server with store tools

They are layers, not rivals. A purchase can be discovered through a UCP profile, carried over MCP and authorised under AP2. The work underneath is shared: complete product data, true availability and totals that do not change after the agent reads them.

What changed in 2026

ChatGPT no longer checks out in the chat by default

ACP launched in September 2025 with Instant Checkout in ChatGPT. In March 2026 OpenAI moved away from it: shoppers now discover products in ChatGPT and buy on the merchant’s site, and there are no fees on those purchases. ACP continued, mainly as the route for product feeds and promotions. Guides that still describe a 4% Instant Checkout fee describe the 2025 model.

UCP went the other way and gained cart and checkout capabilities during 2026. Google’s Universal Cart, built on it, began rolling out in the US in May 2026.

The merchant stays the seller

In every one of these protocols the store remains the merchant of record: it charges the payment through its own provider, handles tax, refunds and fulfilment, and owns the customer relationship. The agent never holds the card number – ACP passes a limited Shared Payment Token, AP2 passes signed mandates, and MCP checkout hands payment to a link.

What a Magento store needs

Magento supports none of these protocols out of the box. In order of payoff:

Clean product data – server-rendered Product JSON-LD with offers.availability, identifiers, shipping and returns.
An ACP product feed for ChatGPT shopping results – see ACP product feed.
A UCP profile that advertises only what you serve – see /.well-known/ucp.
An MCP server, read-only first, when you want assistants to query the live catalogue – see MCP for commerce.

Which to ship first: ACP vs UCP for Magento 2.

Questions

What is an agentic commerce protocol?: A standard that lets an AI agent discover products, build a cart and help complete a purchase with a store, while the store stays the merchant of record. ACP, UCP, AP2 and MCP each cover a different part of that.
What is the difference between ACP and UCP?: ACP comes from OpenAI and Stripe and is mainly how catalogues reach ChatGPT product discovery. UCP comes from Google and partners and covers discovery and transaction on Google’s AI surfaces through a profile at /.well-known/ucp.
Does ChatGPT still have Instant Checkout?: Not as the normal path. In March 2026 OpenAI moved away from checkout inside ChatGPT; purchases that start in ChatGPT now complete on the merchant’s site, with no fees on them.
Who is the merchant of record in agentic commerce?: The store. It charges the payment through its own provider and handles tax, refunds and fulfilment. The agent never holds the card number.
Does Magento support ACP or UCP natively?: No. Magento needs modules or custom work for the product feed, the UCP profile and any agent endpoints.

Sources

Rewritten 28 September 2026 against the ACP (2026-04-17), UCP (v2026-08-25), AP2 (v0.2.0) and MCP (2026-07-28) specification repositories and OpenAI’s March 2026 announcement. Disclosure: we build open-source Magento modules for ACP feeds, UCP and MCP.