A2A Protocol v1.0: What's New, What Changed, and What's Next

A2A Protocol v1.0, released in March 2026 with v1.0.1 as its current patch release, establishes a stable open standard for agent-to-agent discovery and task delegation while introducing significant incompatibilities with v0.3. Key migration changes include member-based message parts rather than a kind field, renamed operations and enum constants, revised HTTP paths and errors, version negotiation through the A2A-Version header, and Agent Cards that advertise multiple versioned interfaces through supportedInterfaces. The release also adds enterprise-oriented capabilities including multi-tenancy, signed Agent Cards, task listing, asynchronous sending, and modern OAuth support, while v1.0.1 clarifies media types, error mappings, and examples without changing the wire format. A2A has moved under Linux Foundation governance through the Agentic AI Foundation, alongside MCP, and its official CLI supports card discovery, requests, streaming, local test servers, and wrapping stdin/stdout programs as A2A services. The material distinguishes protocol conformance from behavioral assurance, noting that conformance tools validate implementation rules while TestMu AI’s Rook evaluates an agent’s functional and security behavior through its endpoint, limited by evidence the remote agent exposes. Planned v1.1 work includes task history, event filtering, bidirectional streaming, structured elicitation, and coding-harness integration, but these roadmap items are not yet released.

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