Agentic Commerce Protocol (ACP): What It Is and How It Works

The Agentic Commerce Protocol (ACP) is an open standard that defines the interaction model between a shopper, their AI agent, and a merchant so the agent can complete a purchase on the shopper's behalf. OpenAI and Stripe released ACP on September 29, 2025, and continue to maintain the specification under the Apache 2.0 license. Stripe described it at launch as a standard that "already powers the new Instant Checkout in ChatGPT." The protocol is currently in beta and uses date-based versioning, with versioned snapshots that should be checked against the current implementation contract.

ACP is one of several open standards shaping agentic commerce. Its checkout component defines: how the agent and the merchant exchange cart, payment, and order information securely while the merchant remains the system of record for the order, payments, taxes, and compliance. Platform enrollment and product selection remain with each AI platform. Implementing a protocol does not automatically list a merchant.

Because ACP is an open standard, businesses can adopt it even if they do not process payments with Stripe. Stripe's implementation is the first compatible reference and OpenAI's implementation powers ChatGPT, but the specification is designed to be processor- and platform-flexible.

What ACP specifies today is the checkout session and the secure sharing of payment credentials among the shopper, agent, merchant, and payment provider. The reference specification covers checkout sessions, capability negotiation, payment handlers (including seller-backed payment handlers), extensions, and discounts. The 2026-04-17 release added cart, feed, orders, authentication, and Model Context Protocol (MCP) compatibility.

What ACP explicitly leaves out of scope are PSP authorization and capture semantics, returns and exchanges, tax configuration, and fraud modeling. Those stay with the merchant's payment service provider and commerce stack.

OpenAI expanded ACP to support product discovery in March 2026, while platform participation remains separately managed. The current OpenAI product-feed reference distinguishes discovery data from an enabled checkout integration. See ChatGPT Product Feed Format for that layer.

ACP defines four participants in a checkout:

• Shopper. The consumer who authorizes the purchase and owns the payment credentials.
• AI agent. The application, such as ChatGPT, that discovers, presents, and completes the purchase on the shopper's behalf. The agent is explicitly not the merchant of record.
• Merchant. The business that owns the product, the order, taxes, and compliance, and remains the system of record for the transaction.
• Payment provider. The merchant's payment service provider, which processes the payment. ACP passes secure payment tokens between the buyer and the business through the agent rather than exposing raw card details to the agent or the merchant.

The flow is a checkout-session lifecycle: the agent creates a checkout session, updates it as the shopper confirms selections, and completes it to create an order, or cancels it. Checkout can complete inside the agent interface, or the merchant can use a redirect mode that hands the shopper back to the merchant's site. Both are valid ACP paths. Which one a shopper sees depends on the merchant's and platform's implementation, not on the protocol.

ACP itself is an open standard with no protocol-level fee. A merchant's costs come from the payment processor and commerce platform it already uses, not from ACP.

Stripe's first compatible implementation uses Stripe's standard payment processing and its Shared Payment Token, so merchants already on Stripe pay their existing Stripe processing rates. Because the specification is processor-flexible, merchants on other payment providers can adopt ACP through their own provider's implementation when one is available.

Be specific when comparing costs. Protocol fees (none for ACP), platform fees from an AI surface, and payment-processing fees from a PSP are three different things, and only the last two ever show up on a merchant's bill.

OpenAI launched Instant Checkout on ACP in September 2025 and retired it in March 2026, moving in-conversation purchases to retailer-built ChatGPT Apps while ChatGPT itself sends shoppers to the merchant's site. ACP continues as the standard for the product feed and for Apps that transact. Announcements describe stages of a rollout, not a permanent list of supported merchants or surfaces.

The ACP site says each AI platform manages participation separately. OpenAI's product-feed reference separates search eligibility from a separately enabled checkout integration. Confirm the current contract for the workflow you intend to deploy.

ACP supports configuring checkouts for physical goods, digital goods, subscriptions, and asynchronous purchases. The specification's fulfillment types include shipping and digital.

Current limitations are mostly about what is out of scope rather than what is unsupported: PSP authorization and capture semantics, returns and exchanges, tax configuration, and fraud modeling all remain with the merchant's existing systems. On the OpenAI commerce onboarding side, prohibited categories include adult content, age-restricted products such as alcohol and nicotine, gambling, harmful or dangerous materials, weapons, prescription-only medications, and unlicensed financial products.

ACP and UCP overlap in commerce functions. Consult their current specifications and the platform’s enabled capabilities rather than assuming either name guarantees a complete journey. MCP sits underneath as the data-access layer. AP2 and A2A are companion standards for payment authorization and agent communication. See the ACP integration checklist for implementation planning.

Checkout is the last step. Before an agent can sell a product it has to find it, trust the title, attributes and description, and prefer it over the alternatives. That product information is the part of ACP readiness an ecommerce team controls, and it matters just as much for stores that never enable in-chat checkout.

This is the work Paz does. A Paz expert looks at your catalog against the questions shoppers ask in ChatGPT and the other AI surfaces, fixes the gaps in the product information that keep products out of answers, and tracks appearances over time. Our experts publish within agreed guidelines and bring exceptions to you. Checkout, payments, orders, and fulfillment remain with the merchant's commerce stack and payment provider. Start with a free check of one product page or read how the AI visibility service works.