Multi-Agent Interop — June 6, 2026

The read

A2A and registries wire agents together — protocol, not moat. Value sits in delegation topology humans design and the institutional rules that govern who can act on whose behalf.

What moved

• Microsoft Foundry ships incoming A2A public preview with versioned agent cards and Entra-gated discovery — Microsoft Foundry Blog At Build 2026, Foundry Agent Service adds incoming Agent2Agent (public preview) alongside existing outbound A2A tools. Any prompt or responses-protocol hosted agent can expose an A2A base path, publish v1.0 and v0.3 agent cards at agentCard/{version}, and accept JSON-RPC delegation from external agents. Agent card fetch and invocation require Microsoft Entra ID (OBO or service identity); anonymous discovery is not supported. Foundry documents A2APreviewTool connections with custom AgentCardPath for cross-agent calls within the same project. Builder angle: Bidirectional A2A on Foundry lets you publish a governed agent card once and accept delegated tasks from LangGraph, ADK, or other A2A clients without rebuilding the agent per partner stack.

• Hosted agents in Foundry add A2A as fourth protocol for cross-agent delegation on production runtimes — Microsoft Foundry Blog Build 2026 updates to hosted agents extend the protocol surface beyond Responses, Invocations (HTTP), and Invocations (WebSocket) with Agent2Agent (A2A) for agent delegation. A single hosted agent can expose multiple protocols simultaneously, including Teams/M365 channel bridging and A2A handoffs. The post also ships direct source-code deployment (python_3_13/3_14, dotnet_10) without container registry, built-in Content Safety guardrails, and Voice Live/WebSocket for real-time voice agents. Builder angle: Adding A2A beside Responses/Invocations means production hosted agents can both answer users and accept delegated sub-tasks from remote specialist agents on the same deployment.

Also tracking

• A2A v1.0 reaches production with Signed Agent Cards and 150+ enterprise adopters — source — Linux Foundation A2A v1.0 (April 9) adds Signed Agent Cards, multi-tenancy, and SDKs in five languages; embedded in Azure Foundry, Copilot Studio, and Bedrock AgentCore Runtime.
• Amazon Bedrock AgentCore Runtime adds native A2A protocol with Agent Card discovery — source — AgentCore hosts stateless A2A servers on port 9000 with SigV4/OAuth inbound auth, session isolation headers, and /.well-known/agent-card.json discovery for cross-framework delegation.