ACP (Agentic Commerce Protocol)

Stripe + OpenAI’s protocol for agent-driven checkout. Card-network-native.

ACP is the Agentic Commerce Protocol developed by Stripe and OpenAI. It defines how AI agents conduct checkout against merchants in the Stripe / OpenAI ecosystem — notably including the OpenAI Agent marketplace and ChatGPT shopping.

Sly provides a full ACP implementation compatible with the published spec, plus server-side policy enforcement (KYA tiers, wallet limits) that ACP itself doesn’t define.

Core concept: the checkout session

ACP works in terms of checkout sessions — stateful objects that represent a purchase in progress. The session transitions through states as the agent and merchant interact.

created ─▶ pending_payment ─▶ paid ─▶ fulfilled
                   │
                   ▼
               failed / expired / cancelled

Create a checkout session (agent side)

curl -X POST https://api.getsly.ai/v1/acp/checkouts \
  -H "Authorization: Bearer agent_..." \
  -H "Content-Type: application/json" \
  -d '{
    "merchant_id": "mer_stripe_...",
    "items": [
      { "sku": "widget-pro", "quantity": 2, "unit_price": "24.99", "currency": "USD" }
    ],
    "shipping_address": { ... },
    "payment_method": "card"
  }'

Response:

{
  "id": "acp_chk_...",
  "status": "pending_payment",
  "total": "49.98",
  "currency": "USD",
  "client_secret": "cs_...",
  "expires_at": "2026-04-22T14:30:00Z"
}

Complete payment

curl -X POST https://api.getsly.ai/v1/acp/checkouts/acp_chk_.../complete \
  -H "Authorization: Bearer agent_..." \
  -d '{
    "payment_method_id": "pm_..."
  }'

Payment is executed synchronously against the card network (or async for deferred methods). On success the session transitions to paid; on failure, to failed with a reason code.

Fulfillment

Merchants report fulfillment back to Sly; buyers poll or subscribe to acp.checkout.fulfilled webhooks:

curl https://api.getsly.ai/v1/acp/checkouts/acp_chk_.../events \
  -H "Authorization: Bearer agent_..."

Endpoints

Endpoint	Purpose
POST /v1/acp/checkouts	Create checkout session
GET /v1/acp/checkouts	List sessions
GET /v1/acp/checkouts/:id	Get session state
PATCH /v1/acp/checkouts/:id	Update (e.g. swap payment method)
POST /v1/acp/checkouts/:id/complete	Complete payment
POST /v1/acp/checkouts/:id/cancel	Cancel session
POST /v1/acp/checkouts/batch	Batch checkout (marketplace baskets)
POST /v1/acp/checkouts/:id/refund	Refund completed checkout

Plus 26+ sub-resource endpoints for items, shipping, discounts, tax calculation, and webhook replay. See API reference for the complete list.

Differences from the canonical ACP spec

Sly’s implementation adheres to the Stripe/OpenAI spec, plus:

• KYA tier enforcement — agents cannot complete checkouts that exceed their KYA tier limits
• Wallet policies — per-merchant allowlists/blocklists enforce at checkout time
• Composition — checkouts can be funded by UCP tokens, AP2 mandates, or x402 bridged payments
• Approval workflow — checkouts above a policy threshold auto-trigger human approval

When to use ACP

• Merchant is on Stripe Connect or listed in the OpenAI Agent marketplace
• Buyer is a ChatGPT agent or OpenAI-ecosystem agent
• You want card-network-native payment (Visa, Mastercard, Amex)
• You need the Stripe / OpenAI compliance posture out of the box

For non-Stripe merchants or non-card rails, prefer UCP.