What does ACP standardise?
Stripe and OpenAI released the Agentic Commerce Protocol at the end of September 2025, alongside Instant Checkout going live in ChatGPT for United States buyers of Etsy listings (Stripe, Payments Dive). Its scope is the merchant-facing half of the purchase: a common way for an agent to read a checkout, submit an order, and hand over a payment credential without ever storing the card itself. The business keeps the customer relationship and controls how its products are presented. It is published under Apache 2.0, and a business that does not process with Stripe can still adopt it with its existing provider (agenticcommerce.dev, Stripe).
What sits outside that scope is the question of whether the person genuinely authorised the spend. ACP's published remit is checkout configuration, credential sharing and transaction coordination, and authorising an agent to buy unattended is not part of it.
What does AP2 standardise?
Google announced the Agent Payments Protocol on 16 September 2025 alongside more than sixty payment and technology companies (Google Cloud). Its unit is the mandate: a cryptographically signed record of what the user asked for and what they agreed to pay, designed to survive an argument afterwards. The launch post described two, an intent mandate carrying the original instruction and its limits, and a cart mandate signed against the exact items and price.
The specification has moved since, and this is worth checking before you quote it. Version 0.2 lists a Checkout Mandate, covering the items and purchase details negotiated with the merchant, and a Payment Mandate, authorising payment against a specific instrument (the AP2 specification). Most comparison pieces still quote the launch names. Read the spec, not the write-ups.
Google donated AP2 to the FIDO Alliance in late April 2026, and standardisation now continues inside FIDO working groups rather than at Google (Google, FIDO Alliance). The same release added human-not-present payments, the case ACP's remit leaves open: the agent buying while you sleep, against limits you set earlier.
Why do people think they compete?
They arrived thirteen days apart, both were introduced as protocols for agent payments, and both came with a long list of card networks and processors attached. Rivalry is the easier story to write.
The tell that it is the wrong story is technical rather than commercial. AP2 was built on top of the Model Context Protocol and Google's Agent2Agent protocol (Google Cloud), and ACP ships an MCP-compatible integration path alongside its REST one (agenticcommerce.dev). Both were designed to sit in the same stack as the same agent plumbing, which is not what two candidates for one job look like.
Where does Google's UCP fit?
Google announced the Universal Commerce Protocol on 11 January 2026, co-developed with Shopify (Google, Shopify). It covers discovery, catalogue, checkout sessions and the handoff back to a human, which puts it on ACP's side of the line rather than AP2's.
Three names, three jobs: find the item and run the checkout, prove the buyer agreed, move the money.
Which one should you build against?
If you are a merchant, the honest answer is that you follow the agent surfaces that actually send you traffic, which today means ACP for ChatGPT and UCP for Google. That decision is a distribution question rather than a standards one, and it will keep changing.
If you are building the agent, you do not get to skip the authorisation layer. Ten years inside payment operations taught me that every dispute eventually collapses into one argument: what was authorised, by whom, and can you show it. A checkout standard has nothing to say about that question, and a signed mandate exists to answer it. Build the layer that survives the argument, and treat the checkout integration as the part you will rewrite twice.