A2A Extensions: Empowering Custom Agent Functionality- Google Developers Blog
Sep 9, 2025Philip Stephens, Junjie Bu, Mike Smith, Chitra Venkatesh
Summary
This post introduces A2A Extensions, a mechanism to add custom, domain-specific functionalities to the A2A protocol. It details the 'helloworld' extension for timestamps, the Traceability Extension with `ResponseTrace` and `Steps` (ToolInvocation, AgentInvocation) for logging agent requests hierarchically, Twilio's Latency Extension for model selection, and Identity Machines' zero-trust handshake implementation. It also mentions Ethereum's ERC-8004 proposal for a trust layer for AI agents.
More from the Agentic Application Middleware trail
- The Outer Loop, Insights First: An Ambient Quality Agent That Diagnoses Your Production Agent- Google Developers Blog
- Supercharge your development with the Google Developer Knowledge API ecosystem- Google Developers Blog
- Turn your REST APIs into MCP tools with Google Cloud API Gateway- Google Developers Blog
- Introducing Support for Local AI Models in the Antigravity SDK- Google Developers Blog
- Why client SDK generation belongs in the open- Google Developers Blog