Stripe and OpenAI release the Agentic Commerce Protocol with Instant Checkout
A checkout-session protocol for agents, distinct from x402’s HTTP 402 challenge.
2025-09
What happened
By September 2025 x402 had been public for four months, MCP for ten, and Visa Intelligent Commerce for five. Google AP2 and Stripe/OpenAI ACP arrived in the same month. The public record still showed announcements and SDKs more than independent payer proof.
OpenAI opens Instant Checkout and publishes ACP as an open standard
ChatGPT becomes a commerce client. Merchants keep their processor.
ACP docs define merchant checkout-session REST endpoints
Five HTTPS JSON endpoints, not an HTTP 402 challenge.
ACP documentation home states the job to be done: programmatic checkout
Agents render checkout state; sellers keep processors. Not HTTP 402.
Machine payments leave the whitepaper phase
By September 2025 x402 had been public for four months, MCP for ten, and Visa Intelligent Commerce for five. Google AP2 and Stripe/OpenAI ACP arrived in the same month. The public record still showed announcements and SDKs more than independent payer proof.
Trade press same-day coverage of AP2 is corroboration, not a primary source
zFinia prefers the Google Cloud post. This record shows how secondary reports are filed.
Google announces the Agent Payments Protocol (AP2)
A payment-agnostic mandate framework meant to sit beside A2A and MCP.
Google publishes the AP2 specification in an open GitHub repo
Mandate-based agent authorization is now a readable spec, not only a keynote.
USDC is the default settlement asset across x402, Base and several agent rails
Circle’s dollar token is the unit most machine-payment demos actually move.
@x402/core becomes the reference TypeScript client/server SDK
Package cadence is a developer-activity signal for the protocol’s real adoption, not GitHub stars.