For the past eighteen months, three acronyms have come up repeatedly in every discussion about agentic commerce: ACP, UCP, and AP2. They are often portrayed as competitors vying for a single standard. This is an inaccurate interpretation, and it leads to poor technical decisions.

The short answer

ACP and UCP are e-commerce transport protocols: they describe how an agent discovers products, builds a shopping cart, and places an order. AP2 is a payment authorization protocol: it describes how to prove that an agent was indeed authorized to pay, and for what amount.

A typical agentic transaction therefore combines both layers: an ACP or UCP transport layer, with an AP2 authorization layer underneath. The question is not “which one to choose over the others,” but “which ones should I support, and in what order.”

The Comparison

	ACP	UCP	AP2
Supported by	OpenAI and Stripe	Google and Shopify	Payment ecosystem, powered by UCP
Type	Commercial transportation	Commercial transportation	Payment Authorization
Scope	Focused on checkout, with a shift toward discovery	Full cycle: discovery, shopping cart, payment, tracking, and after-sales service	Signed authorization, tokenization, proof of intent
Relevant platforms	ChatGPT, Copilot	Google, Shopify, Etsy, Wayfair	Cross-functional
Catalog context exchange	Via the protocol	Relies in particular on MCP	Not applicable
Maturity expected in 2026	Deployed on OpenAI platforms	In production at major merchants	Accepted by banking institutions

ACP: Entry via Payment

ACP was born out of the need to complete a transaction directly from a conversation, without redirecting the user to the merchant’s website. It operates like a delegated checkout funnel: the merchant provides the necessary information to build a valid order, the agent assembles it, and the payment is processed within the conversational context.

What this means for merchants: an entry point capable of creating an order in an idempotent manner, returning the exact taxes and shipping costs, and properly handling product unavailability between the time of the offer and the time of confirmation.

The pitfall: believing that simply setting up an entry point is enough. The real engineering challenge lies in calculating the total price—including taxes and shipping—in real time; an error here leads to a dispute, not an abandoned cart.

UCP: The Full Customer Journey

UCP covers the entire customer journey: discovery, shopping cart, payment, order tracking, and after-sales service. It relies on AP2 for the payment portion and on MCP for context exchange between the merchant’s catalog and the agent’s reasoning engine.

It is the protocol with the broadest functional scope, and the one that has seen the fastest adoption within the ecosystem, notably through its default activation on U.S. Shopify stores in March 2026.

What this means for merchants: the catalog must be semantically queryable, not just exportable as a file. And merchants must be able to answer post-sale questions—such as “Where is my order?”—via a machine interface.

AP2: The Layer No One Can Ignore

AP2 addresses the question that legitimately concerns banks and merchants: how can you prove that an agent was authorized to spend that money? The principle is that of a signed authorization—the user authorizes a limited purchase intent (an amount, a scope, a duration), and the agent presents this proof at the time of payment.

For a merchant, the benefit is clear: liability in the event of a dispute becomes traceable. This is what has garnered support from banking institutions, and it’s why AP2 is included in both transport protocols.

What to Do Depending on Your Situation

You’re on Shopify. UCP is widely supported by the platform. Your focus should be on the quality of your product catalog and the accuracy of your inventory, not on the protocol.
You’re on PrestaShop, Magento, or a custom solution. Start with a clean product feed and an idempotent order API. These two building blocks are essential regardless of which protocol you enable later.
Most of your traffic comes from France or Europe. Don’t rush into a full-scale implementation. Start by cleaning up your data first: this represents the bulk of the effort and benefits all channels, including your marketplaces.
You’re currently redesigning your platform. This is the only scenario where integrating protocols from the design phase actually costs less than adding them later.

Frequently Asked Questions

Do you need to implement all three?

Eventually, probably—but not all at once. AP2 comes with the transport protocol you activate. Start with the one that best suits your platform and your market.

What is the implementation cost?

On a platform that natively supports them, it’s just a matter of configuration. On a custom-built platform, the bulk of the work involves three areas: semantic catalog exposure, real-time total price calculation, and idempotent order creation. The protocol itself is the simplest part.

What happens if a standard disappears?

The groundwork—complete product data, reliable inventory, and a clean order API—remains valid regardless of which protocol survives. That’s why it must be done first.

Do these protocols replace marketplace feeds?

No. They coexist, and they often draw from the same source data. A central product repository feeds both a Mirakl feed and an agentic storefront—see our article on product data.

Conclusion

ACP, UCP, and AP2 aren’t competing with each other—they complement one another. The key decision for a merchant isn’t which protocol to choose; it’s upgrading their product data and order API—a task that benefits all protocols at once and pays off even if they change.

Next in this series: the technical checklist for making your store readable by agents. For a platform that includes these protocols by default rather than as extensions, check out Pixee Commerce.

ACP, UCP, AP2: Which Agentic Commerce Protocol Should You Adopt?