ACP Overview

The Agentic Commerce Protocol — how an agent completes a real checkout inside a conversation.

ACP Overview

The Agentic Commerce Protocol is OpenAI’s specification for ChatGPT Instant Checkout. It lets an AI agent take a buyer from conversation to completed order without leaving the chat — while orders, payments, and compliance stay on your existing commerce stack.

This is the “rails” half of what StateSet builds: the engine an agent runs on, and the protocol it transacts over.

Two specifications

The handler implements both halves:

Spec	What it covers
Agentic Checkout	The merchant checkout API — five endpoints
Delegated Payment	PSP payment vault integration

Delegated payment is what makes this safe: the agent never handles raw card details. A vaulted credential is passed to your payment provider, which authorises it.

The flow

 Buyer in ChatGPT
      │  "order me another bag of the dog food"
      ▼
   Agent ──▶ POST /checkout_sessions          create
         ──▶ POST /checkout_sessions/:id      update — address, shipping, promo
         ──▶ POST /agentic_commerce/delegate_payment
         ──▶ POST /checkout_sessions/:id/complete
                        │
                        ▼
              order created in your stack
                        │
                        ▼
              fulfillment / ERP

Each step is a deterministic API call with a defined response, so an agent can drive it without bespoke per-merchant logic.

Components

Piece	Role
ACP handler	Terminates the protocol; a standalone Rust server
Embedded engine	iCommerce in-process, so a session really reserves inventory
Sync Server	Validation, routing, orchestration to downstream systems
Fulfillment / ERP	Execution and tracking

The handler carries the commerce engine in the same process. There’s no control plane and no network hop between the protocol and the thing that fulfils it — which is why a completed session produces a real order rather than a queued request.

What it enables

• Conversational commerce across ChatGPT, Claude, and custom agents.
• Automated purchasing and reorders — an agent can reorder without a human touching a checkout form.
• One API across channels, rather than an integration per assistant.

Compliance is testable

ACP is a spec, so conformance is a fact rather than an opinion:

npx acp-conformance --url <handler-url> --api-key <key>

The reference implementation ships a spec-compliance matrix documenting exactly which requirements are met.

How ACP relates to UCP and ICP

Protocol	Scope
ACP	ChatGPT Instant Checkout — sessions plus delegated payment
UCP	Platform-neutral checkout interop — discovery, tokenization, OAuth, AP2
ICP	The superset — agent identity, mandates, negotiation, returns, subscriptions, global commerce

ACP is the right target when your buyers are in ChatGPT. ICP subsumes it when you need agent identity, budgets, or peer-to-peer agent commerce.

Related

• ACP Quickstart
• Checkout guide
• ACP Reference