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Google published the AP2 protocol specification this week 1, a transport-layer standard defining how agents communicate payment intent to processors without exposing credential material. AP2 specifies a structured message envelope with fields for amount, currency, merchant identifier, and a single-use authorisation token scoped to each transaction.
The specification is designed for cross-processor interoperability, distinguishing it from network-specific implementations. It draws on the tool-calling semantics of the Anthropic Model Context Protocol 2 and the agent-to-agent communication patterns from Google’s earlier A2A framework 3, consolidating both into a commerce-specific message format.
AP2 is the second publicly available agent-payment specification within five months. Mastercard’s Agent Pay APIs 4 provide a network-specific implementation for the Mastercard card network; AP2 targets the layer above network rails where multiple processors may be addressed by a single agent session.
Two agent-payment specifications now exist in public form: Google’s AP2 and Mastercard’s Agent Pay. Both define mechanisms for agents to initiate transactions; neither had published a formal interoperability mapping with the other as of this week.
Open payment protocol using cryptographically-signed Mandates to authorise agent-led transactions across credit, debit, stablecoins, and real-time transfers; extends A2A and MCP.
Google Cloud Blog