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AP2, ACP and x402 address different parts of agentic payments, not three interchangeable payment rails. AP2 defines authorization and evidence for agent-led transactions; OpenAI’s Agentic Commerce Protocol (ACP) connects ChatGPT commerce to merchant catalogs and checkout systems; and the AP2 FAQ describes x402 as a crypto-payment standard that can be used with A2A. The sources do not establish a complete x402 flow or show that all three compete.
How do AP2, ACP and x402 differ?
| Protocol | Job supported by the cited documentation | Payment and checkout role | What the evidence does not establish |
|---|---|---|---|
| AP2 | Defines agent-payment authorization, mandates, receipts and role responsibilities. The displayed specification is v0.2. | Payment-agnostic according to its FAQ; it is an authorization and evidence layer, not a complete catalog or checkout API. | The specification does not by itself demonstrate broad production adoption. AP2 v0.2 specification; AP2 FAQ. |
| ACP | Defines merchant catalog and checkout integration with ChatGPT, including product feeds, checkout sessions and order updates. | Merchants handle order decisions, payment processing, fulfillment and support, using their existing payment providers. OpenAI says it is not the merchant of record. | Open documentation does not mean every merchant can use live Instant Checkout; participation is for approved partners. ACP key concepts; Agentic Checkout Spec. |
| x402 | The AP2 FAQ identifies it as a crypto-payment standard and points to an implementation used with A2A. | The FAQ says AP2 is payment-agnostic and that alignment with AP2 is planned. | The cited source does not establish a full x402 architecture, current version, supported chains, fees or adoption. AP2 FAQ. |
The practical distinction is layer and responsibility: AP2 focuses on what an agent is authorized to do and what evidence records that authorization; ACP focuses on how ChatGPT interacts with merchant product and checkout systems; x402 is referenced narrowly in AP2’s materials as a crypto-payment standard. A system could involve more than one layer, but the cited sources do not define one universal combined AP2–ACP–x402 flow.
What does AP2 do in an agent payment?
AP2’s v0.2 specification describes an open agent-payment protocol built around mandates and receipts. A mandate records transaction details and authorization; receipts provide evidence associated with the purchase and payment. The specification assigns responsibilities to defined roles rather than treating an AI agent’s own decision as sufficient proof of authorization.
Human-present and autonomous flows
AP2 documentation describes both human-present and human-not-present flows. In the described model, a Shopping Agent assembles mandate contents based on the user’s task, while a Trusted Surface is used to obtain signed Checkout and Payment Mandates. The mandates capture constraints and transaction authorization, so an autonomous flow can still be bounded by user-defined terms rather than treated as unrestricted spending. AP2 specification.
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What the mandates and receipts represent
- A Checkout Mandate and its receipt relate to what is being purchased.
- A linked Payment Mandate and its receipt relate to the payment.
- Role-specific verification and validation help create evidence that can be used in a dispute.
The specification states: “When this document refers to validation or processing for a particular role, it MUST happen in deterministic code regardless of whether the role is agentic or not.” This is a normative requirement in the AP2 v0.2 specification, not a claim that every implementation already follows it.
AP2 is therefore best understood as an authorization and evidence framework that can sit alongside broader commerce protocols. The documentation does not make it a product catalog, merchant order-management system or complete checkout API. It also does not, on its own, establish production adoption.
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How does ACP connect ChatGPT to merchant checkout?
ACP is OpenAI’s open protocol for connecting ChatGPT commerce to merchant product information and checkout. Its documented flow keeps the merchant’s systems central: ChatGPT can discover products through structured feeds, then use merchant checkout endpoints to create and update a checkout session and complete it with an order-state response. ACP key concepts; checkout specification.
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- Create and update a checkout session. ChatGPT calls the merchant’s checkout endpoints. The merchant calculates and validates checkout details.
- Make the order decision. The merchant accepts or declines the order and returns the resulting order state.
- Process payment and fulfill the order. The merchant uses its payment processor and remains responsible for fulfillment and customer support.
Payments and merchant responsibility
ACP’s Delegated Payments approach can pass a limited payment token through a merchant’s trusted payment-service provider. The developer documentation identifies Stripe Shared Payment Token as the first implementation compatible with the Delegated Payment Spec; that does not establish support for every processor or payment method. OpenAI’s documentation says merchants accept or decline orders, charge payment methods and handle fulfillment, and that OpenAI is not the merchant of record. ACP key concepts.
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Open specification versus live access
ACP documentation and integration are open to developers, but Instant Checkout is described as available to approved partners. An open protocol therefore does not automatically give any merchant access to live ChatGPT checkout. ACP key concepts.
OpenAI announced Instant Checkout on September 29, 2025, with an initial U.S. rollout, U.S. ChatGPT Free, Plus and Pro users, initial Etsy seller availability, and single-item purchases. Those are launch-time details, not a verified availability matrix for October 2026; check current partner and regional eligibility in the developer documentation. September 29, 2025 announcement.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What is x402’s relationship to AP2?
The AP2 FAQ describes x402 as a crypto-payment standard and points to an A2A-plus-x402 implementation for crypto payments. It also says AP2 is payment-agnostic and that alignment between the implementation and AP2 is planned over time. This supports a limited relationship: x402 can be used with A2A, and AP2 intends alignment. It does not show that x402 is built into AP2, that the two standards have identical roles, or that their integration is complete. AP2 FAQ.
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Which protocol answers which implementation question?
- “How can an agent’s authority and transaction evidence be represented?” AP2 addresses this through mandates, receipts and defined role responsibilities.
- “How can ChatGPT use merchant product data and checkout?” ACP describes the feed, merchant checkout-session and order-state integration.
- “How might a crypto payment be used with an agent protocol?” The AP2 FAQ points to x402 with A2A, while noting planned alignment with AP2.
These answer different questions. Comparing them as rival payment rails obscures the distinction between authorization, merchant integration and a referenced crypto-payment standard. The official materials cited here also provide no comparable production transaction volumes or adoption counts for the three.
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