Agentic Checkout Spec (developers.openai.com)

OpenAI published the Agentic Checkout Spec to let merchants run end-to-end checkout flows directly inside ChatGPT—Instant Checkout is live for approved partners (applications are open). The spec is designed so ChatGPT drives the UI while merchants retain authoritative order, payment and fulfillment logic on their own commerce stack. That makes it easy to embed conversational buying into chats without moving settlement, tax calculation or fraud controls into OpenAI’s systems. Technically, merchants must implement a small REST surface (POST /checkout_sessions, POST /checkout_sessions/{id}, POST /checkout_sessions/{id}/complete plus optional cancel/GET) that always returns a “rich” cart state (line items, pricing, taxes/fees, shipping, discounts, totals, status) and publish order lifecycle events (e.g., order.created/order.updated) to a supplied webhook so ChatGPT stays in sync with fulfillment-grade truth. Endpoints require HTTPS/JSON and strict headers (Authorization, Idempotency-Key, Request-Id, Signature, Timestamp, API-Version, Accept-Language, User-Agent). Payments stay on the merchant’s PSP (Delegated Payments is optional). The spec emphasizes security (auth, signature verification), idempotency, input validation, retry safety, and conformance checks (schema, error codes, rate limits, webhook reliability). For AI/ML and commerce teams this means higher-conversion, agent-driven shopping is feasible but demands robust backend integration and webhook-driven consistency to avoid order duplication or mismatch in conversational flows.