ACP

The protocol's site describes it as an open standard for programmatic commerce flows between buyers, AI agents and businesses. Its checkout half is specified as a set of REST endpoints for creating, updating and completing a checkout session, published on OpenAI's developer site. The stated purpose is to let merchants run end-to-end checkout flows inside a chat interface, while keeping orders, payments and compliance on their existing commerce stack.

Its payment half is a shared payment token — a scoped grant that lets an agent use a customer's payment method, carrying usage and expiration limits. The merchant keeps its own payment service provider and its own settlement; the token is what the agent is given to present, in place of the credential itself.

Set against the HTTP payment rails it is a different job rather than a competitor. Stripe's integration table places ACP with the protocols for selling through agents, and MPP and x402 with the rails for accepting machine payments — different capabilities rather than ranked alternatives. A machine payment has no catalogue and no cart, which is the whole of the difference.