Discovery gets the attention, but checkout is where agentic commerce becomes real money. The stack settled into layers during 2026: open protocols (ACP for merchant feeds and orders, AP2 for authorization), card networks (Visa Intelligent Commerce, Mastercard Agent Pay with its scoped Agentic Tokens), processors (Stripe's Shared Payment Tokens), and crypto rails (x402 for machine-to-machine payments).
The market spoke on which model leads for retail: after OpenAI retired in-chat Instant Checkout in March 2026, handoff — agent discovers and shortlists, merchant hosts the checkout — became the dominant pattern, with fully delegated payment growing fastest in machine-to-machine contexts (APIs, data, tools) rather than consumer carts.
Yes, but mostly via handoff or tightly scoped credentials. Consumer flows typically end on the merchant's checkout; autonomous payment is furthest along for machine-to-machine purchases like API calls, where x402-style rails settle in stablecoins.