UCP vs ACP: What E-commerce Brands Need to Know About Agentic Commerce Protocols
Google's Universal Commerce Protocol (UCP) and OpenAI's Agentic Commerce Protocol (ACP) are reshaping how AI handles shopping. This article explains what UCP and ACP mean for e-commerce visibility and how to prepare.
Key Takeaways
- Agentic commerce: an AI agent completes the whole buying journey, from discovery to checkout, without the customer visiting the merchant's website.
- Google's Universal Commerce Protocol (UCP) is open-source: UCP powers checkout in Google AI Mode and is developed by Google in collaboration with Shopify, Etsy, Wayfair, Target, and Walmart.
- OpenAI's Agentic Commerce Protocol (ACP) now covers product discovery: OpenAI scaled back Instant Checkout on 4 March 2026, and ChatGPT now hands the purchase to the merchant's own checkout.
- UCP and ACP now cover different stages: UCP runs transactable checkout, and ACP covers the stage where the buyer finds the merchant before leaving to buy.
- Answer engine optimization (AEO) for e-commerce is now about being transactable: when an AI agent cannot complete a purchase through a product, the AI agent recommends a competitor whose product it can transact.
In January 2026, something significant happened that most e-commerce brands missed: Google announced the Universal Commerce Protocol (UCP) at the National Retail Federation (NRF) conference, and OpenAI quietly expanded its Agentic Commerce Protocol (ACP) to more merchants.
UCP and ACP are infrastructure protocols. They decide which products AI agents recommend and which products AI agents can sell on a merchant's behalf.
UCP and ACP are a probable reason why some e-commerce brands' products do not show up in ChatGPT's shopping recommendations or Google's AI Mode.
What Is Agentic Commerce?
Agentic commerce is shopping in which an AI agent acts on behalf of the customer.
Traditional e-commerce: the customer searches, browses, adds products to the cart, and checks out.
Agentic commerce: the customer tells the AI what the customer wants, the AI finds options, and the AI completes checkout.
The AI agent completes the entire shopping journey without the customer visiting the merchant's website. Agentic commerce is already happening in ChatGPT, Google's AI Mode, and Perplexity.
Forecasts for Agentic Commerce Spending
Morgan Stanley Research estimates that agentic shoppers will account for $190 billion to $385 billion of US e-commerce spending by 2030. The Morgan Stanley estimate is a likely 10% share of online retail and up to 20% at the top of the estimate range. Gartner forecasts that by 2028, 90% of B2B buying will be AI-agent intermediated, moving more than $15 trillion of B2B spend through agent exchanges. Neither forecast requires the protocols in this article to succeed in their current form. Both forecasts assume buyers keep arriving through an agent.
Google's Universal Commerce Protocol (UCP)
The Universal Commerce Protocol (UCP) is Google's open-source standard for agentic commerce. Google announced UCP at NRF 2026 and documented it on the Google Developers Blog on 11 January 2026. UCP is designed to let AI agents complete the entire shopping journey, from discovery to checkout to post-purchase support.
Key Features
- Powers checkout in Google AI Mode, Google's AI search experience
- Single integration point: one UCP implementation works across all Google consumer surfaces
- Open-source: compatible with Agent Payments Protocol (AP2), Agent2Agent (A2A), and Model Context Protocol (MCP)
- Partners: developed by Google in collaboration with Shopify, Etsy, Wayfair, Target, and Walmart, and endorsed by Visa, Mastercard, Stripe, Best Buy, and Home Depot
What UCP Means for Your Products
When someone asks Google AI Mode "find me running shoes for flat feet under $150," UCP enables:
- AI to pull product data from Google's Shopping Graph, which Google described in May 2026 as carrying over 60 billion product listings, up from the 50 billion it cited in November 2025
- AI to compare products based on attributes you've provided
- AI to complete checkout without sending the customer to your site
- AI to handle post-purchase support
Products whose feed is not prepared for UCP are left out of the entire Google AI Mode shopping flow.
How Merchants Connect to UCP
Google's UCP documentation gives merchants two routes: integrate checkout logic directly with AI Mode in Google Search and Gemini, or keep using existing Merchant Center shopping feeds to be surfaced during discovery. Neither route requires rebuilding the storefront. Google states that merchants choose which capabilities and extensions to support, and the communication medium that suits their development team: application programming interfaces (APIs), Model Context Protocol (MCP), or Agent2Agent (A2A). The practical read for a brand owner: the existing Merchant Center feed is the entry route to UCP, and the deeper checkout integration is an optional upgrade.
OpenAI's Agentic Commerce Protocol (ACP)
The Agentic Commerce Protocol (ACP) is OpenAI's cross-platform protocol for shopping and payments within ChatGPT and other AI assistants. OpenAI co-developed ACP with Stripe and released it under the Apache 2.0 license in September 2025. The OpenAI developer documentation is the reference implementation for ACP.
Key Features
- Three specifications: Product Feed Spec, Agentic Checkout Spec, Delegated Payment Spec
- Stripe integration: ACP uses a Shared Payment Token for payments, which hands a narrowly scoped credential to the merchant, who charges it through the merchant's own processor
- Open source: released under Apache 2.0 and co-maintained by OpenAI and Stripe
What Changed in March 2026
The version of this page published in January described ACP as a way to buy inside ChatGPT. That January description is no longer how ACP works, and the correction matters more than the original claim.
On 4 March 2026, OpenAI scaled back Instant Checkout, its feature for completing purchases inside ChatGPT. In OpenAI's announcement, the company said the initial version "did not offer the level of flexibility that we aspire to provide," and that OpenAI would allow merchants to use their own checkout experiences while OpenAI focused its efforts on product discovery. Adoption had been thin: Forbes reported Shopify president Harley Finkelstein saying that only about a dozen of Shopify's millions of merchants had gone live.
ACP itself was not discontinued. Checkout.com's April 2026 analysis states that ACP is expanding past payments into product discovery and richer commerce interactions, with two live merchant patterns. The redirect model hands the buyer to the merchant's site or app. The app model has the merchant build the experience inside ChatGPT on OpenAI's software development kit (SDK), using the merchant's own payment infrastructure.
What ACP Means for Your Products
When someone asks ChatGPT "I need a gift for my sister who likes skincare," ACP enables:
- ChatGPT to search and compare products from merchants whose catalog data it can read
- ChatGPT to present product cards with pricing, reviews, specs
- A hand-off to your checkout, on your site or in your ChatGPT app, rather than a purchase completed in the chat
- Order tracking and support through whichever surface you built
Since March 2026, ACP does less for a brand, and the brand's own product data does more. ChatGPT does not take the order, so the product data that decides whether a product makes the ChatGPT shortlist is the whole of a brand's ACP exposure.
UCP vs ACP: The Key Differences
| Aspect | UCP (Google) | ACP (OpenAI) |
|---|---|---|
| Where the purchase completes | Inside Google AI Mode and Gemini | On the merchant's site or in a merchant-built ChatGPT app, since March 2026 |
| Primary Platform | Google AI Mode, Gemini | ChatGPT |
| Feed Source | Google Merchant Center | ACP Product Feed Spec |
| Payment Integration | Google Pay + multiple processors | Delegated payment tokens, merchant's own processor |
| Open Source? | Yes | Yes, Apache 2.0, OpenAI and Stripe maintained |
| Entry route for merchants | Existing Merchant Center feed, deeper checkout integration optional | Structured catalog data; redirect or ChatGPT app for the transaction |
Checkout.com's January 2026 comparison argued that both protocols would coexist, serving different moments of intent across different platforms. As of July 2026, UCP and ACP coexist, but not as an even contest. UCP and ACP cover different stages of the same buying journey. Prepare for both protocols. Expect purchases to complete through UCP or through the merchant's own checkout. Purchases will not complete inside ChatGPT.
What UCP and ACP Mean for E-commerce AEO
AEO for e-commerce now includes being transactable, in addition to being cited.
When an AI agent cannot complete a purchase through a product, the AI agent recommends a competitor whose product it can transact.
The New E-commerce AEO Stack
Missing any layer of the e-commerce AEO stack loses sales.
Action Items for E-commerce Brands
Do This Now
- Audit your Google Merchant Center feed: check that inventory is updated in real time and that product attributes are complete. The feed is the entry route to UCP, and maintaining it is work the merchant already owns.
- Make your catalog readable to ChatGPT: Since March 2026, product discovery is the whole ACP opportunity, so structured, complete product data decides whether ChatGPT shortlists your products.
- Enable guest checkout: guest checkout is required for agentic commerce on both UCP and ACP.
- Integrate Google Pay: Google Pay gives UCP transactions frictionless payment.
Next Quarter
- Add contextual product attributes: describe use cases, for example "best for flat feet, rainy conditions", in addition to the basic description "blue running shoe".
- Implement schema markup: Product, Offer, AggregateRating, and FAQPage at minimum.
- Choose a ChatGPT pattern: redirect buyers to your own checkout, or build a ChatGPT app on OpenAI's software development kit (SDK) with your own payment infrastructure.
- Support delegated payment tokens: delegated payment tokens are the one payment capability both UCP and ACP assume, whichever protocol prevails.
Long-Term (2026-2027)
- Build for multiple AI agents: AI agents, rather than human shoppers, will compare your products.
- Invest in real-time data infrastructure: AI agents penalize stale inventory and pricing instantly.
- Develop agentic customer service: buyers will expect post-purchase support through AI.
Summary: UCP and ACP for E-commerce Brands
UCP and ACP are the new distribution layer for e-commerce, not merely technical plumbing. Brands that integrate early will capture demand that competitors cannot even see.
The shift from "getting found" to "being transactable" is the biggest change in e-commerce since mobile.
FAQ: UCP, ACP, and What Changed
What is the difference between UCP and ACP?
The Universal Commerce Protocol (UCP) is Google's open-source protocol, announced in January 2026. UCP powers checkout inside Google AI Mode and Gemini and takes product data from Google Merchant Center. The Agentic Commerce Protocol (ACP) was co-developed by OpenAI and Stripe, released under Apache 2.0 in September 2025, and operates inside ChatGPT. Since March 2026, ACP's role has narrowed: OpenAI stopped completing purchases inside ChatGPT and now routes buyers to the merchant's own checkout.
Is ChatGPT Instant Checkout still available?
ChatGPT Instant Checkout is not available in its original form. On 4 March 2026, OpenAI scaled Instant Checkout back and said the initial version "did not offer the level of flexibility that we aspire to provide," and that OpenAI would let merchants use their own checkout experiences while OpenAI focused on product discovery. Buyers now discover products in ChatGPT and complete the purchase on the merchant's site or inside a merchant-built ChatGPT app.
Are Shopify and Etsy stores automatically eligible for ChatGPT checkout?
No. Automatic eligibility for ChatGPT checkout was the January 2026 position and no longer applies. Shopify's president said only about a dozen of Shopify's millions of merchants had gone live with ChatGPT checkout before OpenAI pulled it back in March 2026. Treat platform eligibility as a product discovery question: what matters is whether a store's product data is structured well enough for ChatGPT to surface it, not whether checkout is switched on.
Which agentic commerce protocol should an e-commerce brand prioritise?
Prioritise both protocols, for different jobs. UCP runs transactable checkout today, through Merchant Center feeds into Google AI Mode and Gemini. ACP covers discovery inside ChatGPT, with the purchase completing on the merchant's own site. Both protocols require the same prerequisite: complete, accurate, real-time product data.
How does a merchant integrate with Google's UCP?
Google's documentation gives merchants two routes: integrate checkout logic directly with AI Mode in Google Search and Gemini, or use existing Merchant Center shopping feeds to be surfaced during discovery. Merchants choose which capabilities to support and the communication medium that suits them: application programming interfaces (APIs), Model Context Protocol (MCP), or Agent2Agent (A2A).
What do UCP and ACP cost a merchant?
Neither Google nor OpenAI publishes a merchant fee schedule for the protocols themselves in their public documentation, so the widely quoted percentage comparisons circulating in vendor blogs should be treated as unverified. Budget instead for the work that is certain: feed quality, real-time inventory and pricing, and payment infrastructure that can accept delegated payment tokens.
Sources
- Google Developers Blog, Amit Handa and Ashish Gupta (11 January 2026). The UCP announcement: an open-source standard covering discovery, checkout and order management, with Google's first reference implementation in AI Mode and Gemini.
- Google Merchant UCP documentation. The two merchant integration routes (native checkout with AI Mode and Gemini, or existing Merchant Center feeds) and the choice of APIs, MCP or A2A.
- Google, Vidhya Srinivasan (19 May 2026). The Shopping Graph at over 60 billion product listings. The earlier 50 billion listings and 2 billion hourly updates figure comes from Google's 13 November 2025 post.
- OpenAI Developers. The Agentic Commerce Protocol reference documentation.
- OpenAI (March 2026). The Instant Checkout retreat in OpenAI's own words: the initial version "did not offer the level of flexibility that we aspire to provide."
- Forbes, Jason Goldberg (10 March 2026). The 4 March 2026 pullback, the routing of transactions through third-party apps, and Shopify president Harley Finkelstein on the dozen live merchants.
- Checkout.com, Rami Josef (11 January 2026). The original ACP-versus-UCP comparison and the coexistence argument.
- Checkout.com, Rami Josef (20 April 2026). The post-pivot merchant patterns (redirect model and ChatGPT app model) and ACP's extension beyond payments into discovery.
- Search Engine Journal, Alex Moss (12 January 2026). Why agents query APIs, parse feeds and evaluate structured data rather than browsing pages.
- Productsup, Marcel Hollerbach (23 November 2025). How Google Shopping AI Mode works and what feeds it.
- Modern Retail, Allison Smith (6 January 2026). The competitive field for the default shopping interface.
- Morgan Stanley Research. Agentic shoppers at $190 billion to $385 billion of US e-commerce spend by 2030, a likely 10% share of online retail and up to 20%.
- Gartner (21 October 2025). By 2028, 90% of B2B buying AI-agent intermediated, moving over $15 trillion through agent exchanges.
Check Whether AI Can Sell Your Products
Novastacks' Answer Architecture program for e-commerce includes feed optimization, schema implementation, and a UCP and ACP readiness assessment. The free AEO audit shows which brands AI recommends instead of yours.