When we first compared these two protocols in January, they looked like mirror images. Both put a “Buy” button inside an AI conversation, and the question was which one to build first. That symmetry broke in March 2026. OpenAI moved checkout out of ChatGPT, while Google kept adding capabilities to UCP. The two protocols now do different jobs, and the choice between them looks different as a result.
The short answer: UCP is Google’s open standard for agent checkout, and Google says it now enables direct checkout for hundreds of thousands of brands and retailers across its surfaces. ACP is the standard OpenAI and Stripe built for ChatGPT. Since March 2026, its main job is getting your catalog into ChatGPT’s shopping discovery, and checkout happens on your own site or inside an app you control in ChatGPT. If you want checkout inside an AI surface today, UCP is the live path. If you want visibility in ChatGPT, start with an ACP product feed.
UCP vs ACP at a glance
| UCP (Universal Commerce Protocol) | ACP (Agentic Commerce Protocol) | |
|---|---|---|
| Built by | Google, co-developed with Shopify and retail partners | OpenAI and Stripe (Stripe’s docs now also list Meta) |
| Launched | January 2026 | September 2025 |
| Where checkout happens today | Inside Google AI Mode and Gemini, or handed off to the merchant’s site | On the merchant’s own site, or inside a merchant’s own app in ChatGPT |
| Main job today | Agent checkout, multi-item carts, live catalog queries, identity linking | Getting products into ChatGPT through product feeds; payments inside merchant apps |
| How agents find you | Merchant Center feeds; business profiles published on your domain | Product feed onboarded by OpenAI for approved partners |
| Payments | Google Pay in Google’s implementation; modular payment handlers; AP2 for agent payments | Delegated payment tokens through providers such as Stripe, Braintree, Checkout.com and Worldpay |
| Integration | REST, MCP or Agent2Agent (A2A) | Endpoints specified in OpenAPI, with JSON Schemas |
What changed in 2026
| Date | Event |
|---|---|
| September 2025 | OpenAI and Stripe launch ACP to power Instant Checkout in ChatGPT |
| January 2026 | Google launches UCP with Shopify and retail partners |
| March 2026 | OpenAI moves checkout into merchant apps and refocuses ChatGPT on discovery |
| March 2026 | Google adds cart, catalog and identity linking to UCP |
| March 2026 | Shopify switches on Agentic Storefronts across AI channels |
| May 2026 | Google announces Universal Cart and UCP expansion to new categories and countries |
| June 2026 | Visa announces a partnership to bring agent-initiated payments into OpenAI’s products |
| September 2026 | Google expands UCP onboarding in Merchant Center, adding cart transfer to merchant sites |
The March change at OpenAI is the one that reshaped the comparison. An OpenAI spokesperson told Search Engine Land that Instant Checkout was moving to Apps, where purchases happen inside connected services instead of in ChatGPT itself, and that the company would prioritize product search and discovery. ACP survived the change. Digital Commerce 360 noted that transactions touching store stock, sales tax and pricing need constant updates that individual merchant apps handle better, and CNBC reported that product selection had stayed limited and item information wasn’t always current.
Google moved the other way. Its March update added a Cart capability that lets agents add several items from one store at once, and a Catalog capability that retrieves real-time details such as variants, inventory and pricing. In May, Google announced Universal Cart, which works across retailers and lets shoppers pay with Google Pay or move their items to the merchant’s site. The brand stays the merchant of record either way. TechCrunch reported that Google is also expanding UCP to categories such as hotels and local food delivery, and to Canada and Australia, followed by the UK.
ChatGPT’s payment story isn’t finished either. In June, Visa said it will integrate its payment network into OpenAI’s products so agents can make purchases within limits users set, but the companies haven’t said when it will fully launch, which merchants will take part, or what checkout will look like.
The core difference now: where the purchase completes
In January, both protocols answered the same question: how does an AI agent complete a purchase? Today they answer different ones.
UCP answers “how does an agent buy from you inside Google?” Google says UCP already enables direct checkout for hundreds of thousands of brands and retailers across its surfaces. Merchants using the Merchant Center integration hub can also enable cart transfer to their own site. Those new capabilities are rolling out in the US first, with Australia and Canada following early next year.
ACP answers “how does ChatGPT know what you sell?” An ACP integration now starts with a structured product feed that gives ChatGPT the catalog data it needs to index your products and describe them accurately. Onboarding is currently limited to approved partners. Checkout inside ChatGPT is still possible, but only inside a merchant’s own app, which calls a checkout flow the merchant controls with a payment provider such as Braintree.
Shopify’s setup shows the split in practice. ChatGPT works as a discovery-focused referrer, and shoppers complete their purchase on the merchant’s own checkout, in an in-app browser or a new tab. On Google AI Mode, Gemini, Microsoft Copilot and Meta, merchants who turn on direct checkout let shoppers buy without leaving the AI channel. Shopify says its Copilot Checkout is powered by UCP.
Scope: what each protocol covers
UCP covers most of the commerce journey, and the pieces are optional. Its capabilities span discovery, carts, checkout, identity linking and order updates. The January version handled single checkout sessions. The March update filled most of the gaps our original comparison listed as roadmap items. Merchants choose which capabilities to support, so a retailer can start with checkout and add carts or identity linking later.
ACP now centers on feeds and delegated payments. Its published specifications cover the product feed, agentic checkout and delegated payment. In practice, the feed does most of the work for most merchants today, because that is what puts products in front of ChatGPT users.
Discovery: how agents find merchants
This difference from our original comparison still holds, and it matters more now that discovery is ACP’s main job.
ACP uses centralized discovery. Merchants apply to OpenAI, get approved, and send their feed to OpenAI. OpenAI controls which merchants and products appear, and it can remove products or ban sellers who break its policies.
UCP supports decentralized discovery. Businesses publish a UCP profile on their own domain that tells agents which capabilities they support, without a bespoke integration for each pair. In practice, most merchants still reach Google’s surfaces through Merchant Center, where Google has been simplifying UCP onboarding.
The trade-off is control versus reach. A curated ChatGPT catalog gives OpenAI quality control. UCP’s design lets any compliant agent discover a UCP-enabled merchant, not only Google’s.
Payments
ACP relies on delegated payment tokens. The AI surface collects the buyer’s payment selection and passes a scoped token to the merchant, who charges it through a supported provider. The provider list has grown well beyond Stripe: Braintree, Checkout.com and Worldpay all document ACP integrations.
UCP uses modular payment handlers. Merchants declare which payment methods they support, and agents choose among them. In Google’s own implementation, shoppers check out with Google Pay or move their cart to the merchant’s site. UCP works alongside Google’s Agent Payments Protocol (AP2), which Google is extending so users can authorize agents to buy within limits they set.
Integration and transport
UCP gives you a choice: businesses can integrate through REST APIs, Agent2Agent (A2A) or the Model Context Protocol (MCP). That flexibility helps if you are building agent workflows across several AI platforms and business systems. It adds decisions if you only need one straightforward integration.
ACP is specified as OpenAPI endpoints with JSON Schema definitions. Stripe’s documentation lists the latest spec version as April 17, 2026. The practical work for most merchants is the product feed itself: required fields, canonical names and validation rules, not protocol plumbing.
Who supports what
UCP
- Google AI Mode, Gemini and Universal Cart. Early Universal Cart retailers include Nike, Sephora, Target, Ulta Beauty, Walmart, Wayfair, and Shopify merchants such as Fenty and Steve Madden.
- Commerce Inc, Salesforce and Stripe, which Google said in March would implement UCP on their platforms.
- Microsoft Copilot Checkout for Shopify merchants.
ACP
- ChatGPT product feeds, for approved partners, and merchant apps inside ChatGPT.
- Payment providers including Stripe, Braintree, Checkout.com and Worldpay.
Both
- Adobe Commerce has committed to supporting both protocols, and its Stripe and Adyen partnerships support them for transactions. It also introduced a Commerce MCP server that gives developers real-time access to catalog, cart, pricing, inventory, checkout and order data.
- Shopware offers an Agentic Commerce sales channel that generates a product feed for ChatGPT, with registration currently limited to the US. UCP can be configured per sales channel, independently of that feed.
- Shopify supports both through Agentic Storefronts, managed from one admin panel.
What neither protocol solves yet: B2B buying
Both protocols grew out of consumer checkout. For B2B merchants, the closest either has come to account-specific buying is UCP’s identity linking. It lets shoppers on UCP-integrated platforms get the same loyalty or member benefits, such as member pricing or free shipping, that they would get logged in on the retailer’s site.
That is a start. A distributor’s “member price” is a negotiated contract price, and a B2B order also depends on credit status, approval chains, purchase orders and net terms. None of those feature in either protocol’s announced capabilities so far. They live in your ERP and B2B platform. Whichever protocol an agent uses, it will need an authenticated way to reach that data. Our guide to preparing your commerce stack for UCP, ACP and agentic checkout covers the platform side, and our ERP integration services cover the connection to the ERP.
Which should you prioritize?
“UCP or ACP” is still the wrong question. The better question now is which job you need done first.
Prioritize an ACP product feed if:
- Your buyers research in ChatGPT and you want to appear in its shopping answers
- Your own checkout is fast and reliable, because that is where ChatGPT sends buyers
- You are a large retailer considering a dedicated app with in-app checkout in ChatGPT
Prioritize UCP if:
- You want buyers to complete purchases inside an AI surface today
- You already manage feeds in Google Merchant Center
- You sell to US shoppers now, or to Canada, Australia and the UK as Google’s rollout reaches them
Build for both if:
- You run Shopify, where Agentic Storefronts manages both from one place
- You are an enterprise merchant on Adobe Commerce, Shopware or a custom stack, and can keep protocol adapters separate from your business logic
The last point matters more than it did in January. One of the two protocols changed its main job within six months, and its payment layer is changing again. If your checkout logic is tied to a single protocol’s current model, the next change will cost you a rebuild.
The questions to ask instead
- Where do my buyers discover products? ChatGPT-first means a feed and a strong checkout on your own site. Google-first means UCP.
- Where do I want the purchase to happen? Inside an AI surface points to UCP. On your own site means ACP feeds plus your own checkout.
- How clean is my product data? Both protocols depend on accurate price, stock and attributes. Google reports that merchants who adopt its core feed best practices see an average 5% increase in conversions the following month.
- How much of my checkout logic is reachable by API? If promotions, shipping rules or customer-specific pricing only work in the browser, neither protocol can use them.
How we’d approach it on Adobe Commerce, Shopware and Shopify
On Shopify, turn on Agentic Storefronts, then decide per channel whether to allow direct checkout. The work that remains is data quality: attributes, variants, policies and inventory accuracy.
On Shopware, start with the Agentic Commerce sales channel for ChatGPT visibility, and check that variant properties such as color and size map to the feed’s fields before you submit it. Configure UCP on the sales channels that sell into Google’s rollout markets.
On Adobe Commerce, treat the API as the contract. Make sure pricing, stock, shipping and customer-specific rules are available through it, then evaluate the Commerce MCP server and Adobe’s protocol support as the connection layer.
On every platform, start by finding out how AI engines see your store today. Our AI-readiness (GEO) audit checks access, commerce data, citable content, brand accuracy and feeds using public data only.
The bottom line
In January, ACP looked like the faster route to AI checkout and UCP like the broader, slower one. By September, the picture had reversed. UCP is where agent checkout runs at scale today, across Google’s surfaces. ACP’s lasting role is discovery: it decides whether ChatGPT knows your products well enough to recommend them, then sends the buyer to a checkout you own. Agent payments in ChatGPT may return through Visa, but the details aren’t public yet.
Both still reward the same foundations. Accurate product data, checkout logic reachable by API, and reliable order events will serve whichever protocol an agent speaks next year.
Talk to us about UCP and ACP for your store. We’ll look at your platform, where your buyers shop, and your catalog data, and recommend where to start.