ACP vs UCP
ACP is how OpenAI and Stripe describe agent checkout. UCP is how Google and Shopify describe a full commerce conversation. If you are on Shopify, your platform is already in the UCP camp and still feeds ChatGPT as a discovery channel. You rarely pick one spec in a vacuum.
| ACP | UCP | |
|---|---|---|
| Who published it | OpenAI and Stripe | Google and Shopify, with Etsy, Wayfair, Target, Walmart on the launch set |
| First public date | 29 Sep 2025 | 11 Jan 2026 (NRF). Profile version 2026-01-11 |
| License | Apache 2.0 | Open spec at ucp.dev |
| Job | Checkout session an agent can create, update, complete, cancel | Discovery through fulfillment. Agents and merchants advertise capabilities |
| How you find it | Partner integration. No well-known URL in the early spec | GET /.well-known/ucp JSON profile |
| Where you feel it | ChatGPT shopping (now mostly send-to-merchant checkout) | Google AI Mode, Gemini, Shopify agentic storefronts |
They are not substitutes
ACP started as a checkout API for Instant Checkout. That product went away in March 2026. The protocol repo is still maintained. Stripe still wants delegated payment tokens. If you take Stripe and want ChatGPT-shaped agents to pay, ACP is the language they published.
UCP is a capability handshake. Merchant says checkout, fulfillment, which wallets. Agent says what it can do. The protocol negotiates. Payments are not "must be Stripe." Shop Pay and Google Pay show up in Shopify's examples. That matches Google's shopping surfaces.
A small Shopify shop does not implement either spec by hand. Shopify already chose UCP and still lists ChatGPT as a referrer. WooCommerce, BigCommerce, and Magento shops are in a different boat: you or your agency pick a plugin. That is a later piece.
How to decide
Already on Shopify: open Agentic in admin. Read the Shopify page. You are not choosing ACP vs UCP in a vacuum.
On Stripe, not Shopify, and you care about ChatGPT: read the ACP repo and Stripe's current agentic docs. Confirm Instant Checkout is gone so you do not build for a button that does not exist.
Building an agent that must talk to many merchants: UCP's well-known profile is the thing you can crawl. ACP still looks partner-specific. That may change. Date-check the repos.
Sources: ACP GitHub, Shopify UCP, ucp.dev, Shopify agentic storefronts.
September 2026.