What Is UCP? The Universal Commerce Protocol Explained for eCommerce Merchants
What is UCP? The Universal Commerce Protocol lets AI agents search, cart and check out in your store. How it works and what merchants must prepare.
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ACP vs UCP: Which Agentic Commerce Protocol Should Merchants Support?
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Key takeaways
- Two protocols, one goal: ACP (Agentic Commerce Protocol) and UCP (Universal Commerce Protocol) both let an AI agent complete a purchase in an online store.
- Different origins: OpenAI and Stripe built ACP and announced it on 29 September 2025. Google built UCP with Shopify and announced it on 11 January 2026.
- Same merchant role: under both protocols you stay the merchant of record and keep the customer relationship.
- A lot of shared groundwork: clean product data, live stock and price, a checkout endpoint and a compatible payment provider serve both.
- Check your platform first: Shopify and the large payment providers already support both, so the decision often starts with what your platform handles for you.
Merchants who read about agentic commerce meet two acronyms very quickly. ACP and UCP appear in the same articles, and it is easy to assume you must pick one. This guide explains what each protocol does, where they differ, what changed in 2026, and what to prepare first.
The short version
ACP is an open standard for connecting buyers, their AI agents and businesses to complete purchases. OpenAI and Stripe maintain it as founding maintainers under an Apache 2.0 license, and ChatGPT is its main surface.
UCP is an open standard that covers the shopping journey from discovery to post-purchase support. Google announced it at NRF 2026 together with Shopify, and Etsy, Wayfair, Target and Walmart co-developed it. Its main surfaces are AI Mode in Google Search and the Gemini app.
In short: ACP grew out of ChatGPT and Stripe. UCP grew out of Google and Shopify. Both describe how an agent talks to a store.
How the two protocols arrived
The order of events explains much of the confusion, because both protocols changed quickly in 2026.
- 29 September 2025: OpenAI and Stripe announce ACP together with Instant Checkout in ChatGPT.
- 11 January 2026: Google announces UCP at NRF.
- 19 March 2026: Google adds Cart, Catalog and Identity linking as optional UCP capabilities.
- 24 March 2026: OpenAI shifts ChatGPT shopping toward product discovery and deprioritizes Instant Checkout.
- 17 April 2026: the latest stable ACP spec version, 2026-04-17, is released.
ACP in detail
ACP asks a merchant to implement three flows.
- Product feed. You share a secure, regularly refreshed feed in CSV or JSON with product details, pricing, inventory and fulfillment options. ChatGPT uses it for search and shopping.
- Checkout. The agent collects buyer information and calls your endpoints. You validate the order, determine fulfillment options, calculate and charge sales tax, and accept or decline the order on your own systems.
- Delegated payment. OpenAI shares payment details securely with your payment service provider, which processes the transaction. Stripe's Shared Payment Token is the first implementation compatible with the Delegated Payment Spec.
OpenAI is not the merchant of record under ACP. You bring your own payment provider and handle payments as you would for any other digital transaction. The protocol is in beta and has shipped several dated spec versions, from 2025-09-29 to 2026-04-17. The spec now covers cart management, order tracking and MCP integration as well as checkout.
Before going live, OpenAI expects testing in a sandbox. That covers session creation, shipping option updates, payment tokenization, order completion and webhook delivery with valid HMAC signatures. All traffic to your endpoints must use TLS 1.2 or later.
UCP in detail
For a step-by-step explanation of UCP itself, see What Is UCP?.
UCP starts from a public profile that your store publishes at /.well-known/ucp. The profile lists the protocol version, the services and capabilities you support, your payment handlers and your public signing keys.
Agents publish a profile of their own, and the two sides compute the capabilities they both support. The specification calls this capability negotiation. Because profiles carry signing keys, an agent can verify who it is talking to without a pre-arranged API key.
UCP defines five capabilities: Catalog, Cart, Checkout, Identity linking and Orders. Merchants choose which ones to support. It offers four transports: REST, MCP, A2A and an embedded protocol for host-to-context communication.
Payments run through pluggable payment handlers declared in the profile. AP2 (Agent Payments Protocol) acts as the payment layer inside UCP and provides cryptographic proof of the shopper's authorization. Your payment provider must be able to process Google's tokens, and you remain the merchant of record.
On Google surfaces, a Merchant Center account with complete product feeds, brand assets and return policies is still required. Native checkout is the default path, and an iframe-based embedded checkout is available for complex checkout flows.
ACP vs UCP at a glance
Two details in the comparison matter more than the rest.
- Discovery works differently. ACP starts from a feed you share with OpenAI. UCP starts from a profile you host yourself, although Google surfaces also use your Merchant Center feed.
- The roles look alike. Under both protocols the merchant keeps the order, the customer data and the payment relationship.
What changed for ChatGPT in March 2026
On 24 March 2026, OpenAI revamped shopping in ChatGPT. It said the first version of Instant Checkout "did not offer the level of flexibility that we aspire to provide," and refocused on product discovery. Merchants keep their own checkout, and they can build ChatGPT apps for deeper integrations.
Forrester reported that Walmart saw conversion rates about three times lower for products sold inside the ChatGPT checkout than for products that sent shoppers to its own site. OpenAI named Target, Sephora, Nordstrom, Lowe's, Best Buy, The Home Depot and Wayfair among the retailers that integrated ACP for product discovery. Shopify Catalog feeds product data into ChatGPT.
What this means in practice:
- For ChatGPT, product data quality decides whether your products appear and how accurately agents describe them.
- For Google surfaces, UCP checkout lets an agent complete the purchase with you directly.
- For both, the shopper can still end up on your own site, so your site must stay fast and consistent with the feed.
Do you need to choose?
Often the platform decides for you. Shopify says merchants can sell in ChatGPT, Microsoft Copilot, Google AI Mode and the Gemini app, and manages product data centrally from Shopify Admin through Agentic Storefronts. Forrester notes that payment providers such as Adyen, PayPal, Stripe and Worldpay are positioning themselves as connectors, building support for several protocols rather than one.
A practical way to decide:
- On Shopify: confirm which AI channels are enabled in Agentic Storefronts, and focus on the quality of your catalog data.
- On Magento, BigCommerce or a custom stack: build the shared groundwork first, then add each protocol's specific pieces as your platform or partners support them.
- If you want ChatGPT visibility: start with the product feed and keep stock and prices fresh.
- If you want Google checkout: prepare the Merchant Center feed, the checkout endpoint and the /.well-known/ucp profile.
What to do this month
- Audit product data. Check titles, descriptions, GTINs, prices, availability and return policy for every product that should be agent-visible.
- Check stock and price freshness. Agents commit to a purchase based on what your feed says, so delays create failed orders.
- Review your payment provider. Ask whether it supports Stripe Shared Payment Tokens for ACP and Google's tokens and AP2 for UCP.
- Map your checkout. List the endpoints that return pricing, tax and shipping options, and check they can run without a browser session.
- Ask your platform for its roadmap. Find out which protocols it supports today and which it plans to support.
If you want to know which of these your store already meets, our agentic commerce readiness audit checks it in one week for a fixed price.
FAQ
Do I have to choose between ACP and UCP?
No. The protocols serve different AI surfaces, and platforms such as Shopify support several of them. Choose based on where your customers shop and what your platform already handles.
Which protocol is more open?
Both are open standards. ACP is published on GitHub under Apache 2.0 and maintained by OpenAI and Stripe. UCP is open and co-developed by a wider group of companies, which ucp.dev lists as including Google, Shopify, Etsy, Wayfair, Target, Walmart, Amazon, Microsoft, Meta, Salesforce and Stripe.
Who is the merchant of record?
You are, under both protocols. OpenAI states it is not the merchant of record in ACP, and Google states that merchants remain the merchant of record in UCP.
Is ACP still relevant after OpenAI dropped Instant Checkout?
Yes. OpenAI shifted its focus to product discovery, and retailers integrated ACP for that purpose. The protocol continues to ship spec versions, and the latest stable one is dated 17 April 2026.
Conclusions
Where should a small store start?
With the shared groundwork: accurate product data, live stock and prices, and a payment provider that supports agent payments. These help under both protocols.
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