# ACP (Agentic Commerce Protocol) - Definition > What ACP is, what changed with Instant Checkout in March 2026, what the 2026-04-17 release covers, and what it leaves out. Source: https://angeo.dev/acp-definition/ Updated: 2026-10-09 Canonical definition # ACP (Agentic Commerce Protocol) - Definition **Agentic Commerce Protocol (ACP) is an open standard that defines how a shopper, their AI agent and a merchant interact so the agent can help complete a purchase on the shopper's behalf.** It was co-developed by OpenAI and Stripe, announced on 29 September 2025, and is maintained on GitHub under Apache 2.0. The design keeps the merchant as merchant of record: the agent never holds the buyer's card number, and the merchant charges through its own payment provider. **In one sentence** An open interaction model between buyer, AI agent and business - launched for in-chat checkout, and since March 2026 mainly the route by which a merchant's catalogue reaches ChatGPT product discovery. ## Current version ACP uses date-based versioning and is still labelled beta. The latest stable snapshot is **2026-04-17**, which added cart, feed, orders, authentication and MCP compatibility. Previous releases: 2025-09-29 (initial), 2025-12-12 (fulfillment), 2026-01-16 (capability negotiation), 2026-01-30 (extensions, discounts, payment handlers). ## What changed in March 2026 **OpenAI stepped back from Instant Checkout; the protocol continued** ACP launched alongside Instant Checkout in ChatGPT, live first with US Etsy sellers and later a set of Shopify brands. On 24 March 2026 OpenAI said it was moving away from a standalone in-chat checkout and extending ACP toward product discovery instead: merchants share feeds and promotions over the protocol, and the purchase completes on the merchant's own site or app. OpenAI's shopper help pages still mention in-chat checkout for some eligible products, so treat it as an exception rather than the normal path. This matters for how you read older material. Guides written before March 2026 describe in-conversation checkout as the default. The specification, the feed format and the merchant-of-record design all continued. The feed itself is described in [ACP product feed](https://angeo.dev/acp-product-feed-definition/). ## The four actors | Actor | Role | | Shopper | Authorizes the purchase and owns the payment credentials | | AI agent | Discovers, presents and - where supported - completes the purchase. Never the merchant of record | | Merchant | System of record: catalogue, pricing, branding, fulfillment, disputes | | Payment provider | Processes the charge the merchant initiates | ## What ACP explicitly leaves out The specification is deliberately narrow. Out of scope: payment-provider authorization and capture semantics, returns and exchanges, tax configuration, and fraud modelling. Merchant onboarding is also not part of the protocol - each AI platform runs its own programme. That last point is the one merchants most often miss: implementing ACP does not by itself put products in ChatGPT. The platform's merchant programme decides that, and OpenAI says a store can also appear through ordinary crawling if OAI-SearchBot is allowed. ## Two different things are called "ACP" **Agentic Commerce Protocol vs Agent Client Protocol** The *Agentic Commerce* Protocol covers purchases. The *Agent Client* Protocol - same acronym - connects AI agents to editors and command-line tools. If a page discusses IDE integrations, it is not about commerce. ## ACP and UCP compared | | ACP | UCP | | Maintainers | OpenAI and Stripe | Google with Shopify, Etsy, Target, Walmart, Wayfair and others | | Licence | Apache 2.0 | Open source | | Latest stable | 2026-04-17 | 2026-08-25 | | Primary surface | ChatGPT product discovery | Google AI surfaces, discovery and transaction | | Discovery artefact | Product feed pushed to the platform | Profile pulled from `/.well-known/ucp` | The prerequisites overlap almost entirely - complete product data, coherent prices, real availability, accessible pages - so most of the work counts twice. Full comparison: [ACP vs UCP for Magento 2](https://angeo.dev/acp-vs-ucp-for-magento-2/). ## What a Magento store implements For most merchants the practical ACP surface is the product feed and the REST endpoints around it, not a checkout integration: - [angeo/module-openai-product-feed](https://angeo.dev/modules/openai-product-feed/) - an ACP-conforming feed, cron-scheduled, multi-store - [angeo/module-openai-product-feed-api](https://angeo.dev/modules/openai-product-feed-api/) - bearer-authenticated REST endpoints for feeds, paginated products with variants, and promotions Both are MIT-licensed. Walkthrough: [preparing a Magento 2 store for ChatGPT Shopping](https://angeo.dev/magento-2-chatgpt-shopping-registration/). ## Questions Can an AI agent still complete a checkout in ChatGPT using ACP? Mostly not. In March 2026 OpenAI moved away from standalone Instant Checkout, and purchases now normally complete on the merchant's own site or app. OpenAI's help pages still mention in-chat checkout for some eligible products. What is the current ACP version? 2026-04-17 is the latest stable snapshot. It added cart, feed, orders, authentication and MCP compatibility. The specification is still labelled beta. Does implementing ACP put my products in ChatGPT? Not by itself. Merchant onboarding is run by the platform, not by the protocol. OpenAI's merchant programme decides which feeds are used, and a store can also appear through ordinary crawling if OAI-SearchBot is allowed. Who stays the merchant of record under ACP? The merchant. The agent never holds the buyer's primary account number, and the merchant charges through its existing payment provider while keeping catalogue, pricing, branding, fulfillment and dispute handling. Is ACP the same as the Agent Client Protocol? No, they share an acronym and nothing else. The Agentic Commerce Protocol covers purchases; the Agent Client Protocol connects AI agents to editors and command-line tools. ### What was the 4% ACP fee, and does it still apply? In 2025, merchants who sold through Instant Checkout inside ChatGPT paid OpenAI a fee on each purchase. It was widely reported as 4% for Shopify merchants, on top of normal payment processing. On 24 March 2026 OpenAI stepped back from Instant Checkout. It now says there are no fees on purchases that start in ChatGPT, because those purchases complete on the merchant's own site. So a 4% figure in an ACP guide describes the 2025 Instant Checkout model, not today's feed-based route. Sharing a product feed under ACP has no fee. ## Related - [ACP product feed - definition](https://angeo.dev/acp-product-feed-definition/) - [UCP - definition](https://angeo.dev/ucp-definition/) - [Agentic checkout - definition](https://angeo.dev/agentic-checkout-definition/) - [ACP vs UCP: which to implement first](https://angeo.dev/acp-vs-ucp-for-magento-2/) - [Module: ChatGPT Shopping feed](https://angeo.dev/modules/openai-product-feed/) Verified 28 August 2026 against the ACP specification repository and OpenAI's March 2026 announcement; March 2026 wording re-checked against OpenAI's merchant page in September 2026. Version and status change frequently - re-check before relying on the dates above. Disclosure: we publish the open-source ACP feed modules referenced here. ## More on this topic - [Merchant of Record - Definition](https://angeo.dev/merchant-of-record-definition/) - [Agentic Commerce Protocols (ACP, UCP, AP2, MCP)](https://angeo.dev/agentic-commerce-protocol-definition/) ## Sources - [Agentic Commerce Protocol - official site](https://www.agenticcommerce.dev/) - [ACP specification on GitHub](https://github.com/agentic-commerce-protocol/agentic-commerce-protocol) - [OpenAI: Powering product discovery in ChatGPT (24 March 2026)](https://openai.com/index/powering-product-discovery-in-chatgpt/) - [OpenAI: Product Feed Spec](https://developers.openai.com/commerce/specs/file-upload/products) Links checked 23 September 2026.