A2A v1 Compatibility Matrix

Last reviewed: 2026-08-10.

This matrix records the repository-backed compatibility status for the Agent2Agent v1 line. A2A Mesh targets the official v1.0 method surface and keeps selected legacy aliases only where they are already covered by tests.

Method surface

A2A operation	Runtime	Client SDK	CLI	REST binding	SSE	WebSocket	gRPC	Verification	Status
message/send	handleRpcRequest	sendMessage	a2amesh send	POST /message:send	Not required	Contract transport	Contract transport	Unit, integration, conformance, examples	Supported
message/stream	SSE handler	sendMessageStream	Conformance command	POST /message:stream	Canonical path	Contract transport	Contract transport	Unit, integration, conformance, transport contract	Supported
tasks/get	Task lookup with authz	getTask	a2amesh task status	GET /tasks/{taskId}	N/A	Contract transport	Contract transport	Unit, integration, transport contract	Supported
tasks/list	Task listing with tenant/context filters	listTasks	Registry/task flows	GET /tasks	N/A	Contract transport	Contract transport	Unit, performance smoke, transport contract	Supported
tasks/cancel	Lifecycle transition guard	cancelTask	Task command path	POST /tasks/{taskId}:cancel	N/A	Contract transport	Contract transport	Unit, integration, transport contract	Supported
tasks/resubscribe	Streaming reattach	subscribeTask	Conformance command	GET /tasks/{taskId}:subscribe	Canonical path	Contract transport	Contract transport	Unit, conformance, transport contract	Supported
tasks/pushNotificationConfig/create	Callback config normalization and storage	createPushNotificationConfig	N/A	POST /tasks/{taskId}/pushNotificationConfigs	N/A	Contract transport	Contract transport	Unit, integration, transport contract	Supported
tasks/pushNotificationConfig/get	Config lookup	getPushNotificationConfig	N/A	GET /tasks/{taskId}/pushNotificationConfigs/{configId}	N/A	Contract transport	Contract transport	Unit and transport contract	Supported
tasks/pushNotificationConfig/list	Config list result	listPushNotificationConfigs	N/A	GET /tasks/{taskId}/pushNotificationConfigs	N/A	Contract transport	Contract transport	Unit and transport contract	Supported
tasks/pushNotificationConfig/delete	Config removal	deletePushNotificationConfig	N/A	DELETE /tasks/{taskId}/pushNotificationConfigs/{configId}	N/A	Contract transport	Contract transport	Unit and transport contract	Supported
GetExtendedAgentCard	Official-v1 mapping to authenticated card lookup	getExtendedAgentCard	N/A	GET /extendedAgentCard	N/A	Not exposed	Not exposed	Unit, integration, conformance	Supported
agent/getAuthenticatedExtendedCard	Mesh compatibility method retained	getAuthenticatedExtendedCard	N/A	JSON-RPC only	N/A	Not exposed	Not exposed	Unit, integration, conformance	Mesh compatibility
agent/authenticatedExtendedCard	Legacy alias retained	authenticatedExtendedCard	N/A	JSON-RPC only	N/A	Not exposed	Not exposed	Unit and integration tests	Legacy alias

Protocol negotiation and metadata

Capability	Implementation	Verification	Status
A2A-Version header negotiation	Runtime HTTP middleware, client headers, WebSocket query negotiation, gRPC metadata paths	Unit, transport, and compatibility tests	Supported
application/a2a+json REST media type	REST binding responses and protocol-version errors	Unit tests	Supported
Required extension rejection	Runtime message configuration validation	Unit and integration tests	Supported
Optional extension passthrough	Task/message extension propagation	Unit tests and golden traces	Supported
Agent Card signing	Runtime/registry signing and verification helpers	Unit tests and registry hardening tests	Supported
JSON-RPC error normalization	Official-v1 response projection plus REST semantic/status mapping; mesh codes stay compatible	Unit, fuzz, and integration tests	Supported
Tenant-aware task authorization	Runtime and registry request context filters	Unit and integration tests	Supported

Official v1 JSON-RPC method names are projected to the A2A v1 error identities at the response boundary. GetTask task misses use TaskNotFoundError (-32001), terminal CancelTask requests use TaskNotCancelableError (-32002), terminal message/subscribe lifecycle failures use UnsupportedOperationError (-32004), and required-extension failures use ExtensionSupportRequiredError (-32008). The equivalent REST routes use the same semantic mapping for HTTP status and problem details. Legacy Mesh JSON-RPC method names retain their historical internal error codes for compatibility.

The conformance fixtures additionally execute the exact public Agent Card discovery path, validate interface and extension metadata, reject unsupported required extensions and protocol versions, and compare JSON-RPC/REST task and push configuration results. SSE version rejection runs in the same suite. WebSocket and gRPC implement the canonical A2A v1 operation set declared by the shared transport contract. Transport-specific framing, authentication hooks, malformed input handling, stream cleanup, and version rejection are exercised by their package tests.

Fixture ownership

Fixture surface	Repository evidence	Profile/classification	Owning area	Required gate
Version negotiation	tests/conformance/fixtures/compatibility/version-negotiation.json	Official v1.0 default, legacy 0.3, experimental v1.2 opt-in	Protocol and runtime	Conformance plus shared transport contract
Authenticated extended card	tests/conformance/fixtures/compatibility/authenticated-extended-card.json	Canonical official method, Mesh compatibility method, and legacy alias	Runtime and security	Conformance
Signed Agent Card trust	tests/conformance/fixtures/compatibility/signed-agent-card.json	Official v1.0	Security and interop	Conformance and schema checks
Cross-transport version rejection	tests/transport-contract/transportContract.ts	Shared HTTP/SSE, WebSocket, and gRPC behavior	Transport maintainers	Transport contract and package unit tests

The compatibility fixtures are offline and checked in. Signed-card evidence contains only public keys, compact JWS values, the canonical payload, and its SHA-256 digest. Private keys must never be committed. When rotating fixture keys, security reviewers own the trust-failure cases, protocol reviewers own the canonical payload and profile classification, and transport maintainers own their contract adapters. The detailed fixture maintenance rules live beside the fixtures in tests/conformance/fixtures/compatibility/README.md.

Compatibility policy

• Official v1.0 methods must be covered by at least one runtime test and one integration or conformance test before they are marked supported.
• Legacy aliases may remain only when they are documented and covered by tests.
• Experimental v1.2 features must require explicit opt-in and must not replace the v1.0 default path.
• New transports must share the same task lifecycle, error, version-negotiation, and authorization semantics as HTTP JSON-RPC.