The AP2 Protocol (Agent Payments Protocol) is an open protocol developed by Google to establish a secure, interoperable framework for AI agent-initiated payment transactions. AP2 can be used as an extension of the Agent2Agent (A2A) protocol and Model Context Protocol (MCP), establishing a payment-agnostic framework for users, merchants, and payment providers to transact with confidence across all types of payment methods. The startup is AP2 protocol documentation site.