feat(spec): Provide ability for SDKs to be backwards compatible. by herczyn · Pull Request #1401 · a2aproject/A2A

herczyn · 2026-01-22T16:14:45Z

fixes #1417
for context see #1416

…nterface.

gemini-code-assist · 2026-01-22T16:16:04Z

Summary of Changes

Hello @herczyn, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on enhancing the gRPC API definitions and improving backward compatibility for agents. It streamlines gRPC configurations by removing redundant bindings and introduces explicit protocol versioning for agent interfaces. Additionally, it deprecates older transport-related fields in the AgentCard message, signaling a shift towards newer, more standardized transport mechanisms.

Highlights

gRPC API Updates: Modified the a2a.proto file to streamline gRPC API definitions by removing redundant additional_bindings in google.api.http options for methods like GetTask, ListTasks, SubscribeToTask, GetTaskPushNotificationConfig, ListTaskPushNotificationConfig, GetExtendedAgentCard, and DeleteTaskPushNotificationConfig.
Agent Interface Enhancements: Added protocol_versions field to the AgentInterface message in a2a.proto to explicitly define supported A2A protocol versions, ensuring backward compatibility. The field is required and should list the latest supported minor version per major version (e.g., ["0.3", "1.0"]).
AgentCard Deprecation: Deprecated several fields in the AgentCard message of a2a.proto, including url, preferred_transport, and additional_interfaces. These fields are marked as deprecated and are intended for use only with the 0.3 version of the transport, indicating a move towards newer transport mechanisms.

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Code Review

The pull request effectively addresses backward compatibility concerns by refining the A2A protocol's versioning strategy. The relocation of protocol_versions from AgentCard to AgentInterface is a logical improvement, allowing for more granular versioning per transport. The deprecation of older fields in AgentCard with clear comments is a good practice for maintaining backward compatibility while signaling future removals. The changes also include some minor formatting adjustments in the additional_bindings sections, with a suggestion to maintain multi-line formatting for readability.

specification/grpc/a2a.proto

…lity' into backwards_compatibility

herczyn · 2026-01-27T21:07:27Z

/vote

git-vote · 2026-01-27T21:07:29Z

Vote created

@herczyn has called for a vote on feat(spec): Provide ability for SDKs to be backwards compatible. (#1401).

The members of the following teams have binding votes:

Team
@a2aproject/a2a-tsc

Non-binding votes are also appreciated as a sign of support!

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The vote will be open for 11months 29days 3h 50m 24s. It will pass if at least 51% of the users with binding votes vote In favor 👍. Once it's closed, results will be published here as a new comment.

git-vote · 2026-01-28T21:25:41Z

Vote status

So far 0.00% of the users with binding vote are in favor and 0.00% are against (passing threshold: 51%).

Summary

In favor	Against	Abstain	Not voted
0	0	0	8

Binding votes (0)

User	Vote	Timestamp
@muscariello	Pending
@darrelmiller	Pending
@geneknit	Pending
@hughesthe1st	Pending
@ToddSegal	Pending
@000-000-000-000-000	Pending
@SivaNSAP	Pending
@spetschulatSFDC	Pending

Non-binding votes (2)

User	Vote	Timestamp
Tehsmash	In favor	2026-01-28 9:05:01.0 +00:00:00
herczyn	In favor	2026-01-28 13:48:56.0 +00:00:00

muscariello

LGTM

herczyn · 2026-01-29T13:02:37Z

LGTM

i assume we still wait for the vote, right?

muscariello · 2026-01-29T17:51:32Z

@ToddSegal @geneknit @spetschulatSFDC @SivaNSAP @hughesthe1st

git-vote · 2026-01-29T21:26:31Z

Vote status

So far 75.00% of the users with binding vote are in favor and 0.00% are against (passing threshold: 51%).

Summary

In favor	Against	Abstain	Not voted
6	0	0	2

Binding votes (6)

User	Vote	Timestamp
SivaNSAP	In favor	2026-01-29 19:22:55.0 +00:00:00
ToddSegal	In favor	2026-01-29 19:20:50.0 +00:00:00
darrelmiller	In favor	2026-01-29 0:25:48.0 +00:00:00
geneknit	In favor	2026-01-29 19:04:36.0 +00:00:00
muscariello	In favor	2026-01-29 12:42:57.0 +00:00:00
spetschulatSFDC	In favor	2026-01-29 19:20:21.0 +00:00:00
@hughesthe1st	Pending
@000-000-000-000-000	Pending

Non-binding votes (3)

User	Vote	Timestamp
Tehsmash	In favor	2026-01-28 9:05:01.0 +00:00:00
herczyn	In favor	2026-01-28 13:48:56.0 +00:00:00
holtskinner	In favor	2026-01-29 15:49:14.0 +00:00:00

git-vote · 2026-01-30T09:26:07Z

Vote closed

The vote passed! 🎉

75.00% of the users with binding vote were in favor and 0.00% were against (passing threshold: 51%).

Summary

In favor	Against	Abstain	Not voted
6	0	0	2

Binding votes (6)

User	Vote	Timestamp
@SivaNSAP	In favor	2026-01-29 19:22:55.0 +00:00:00
@ToddSegal	In favor	2026-01-29 19:20:50.0 +00:00:00
@darrelmiller	In favor	2026-01-29 0:25:48.0 +00:00:00
@geneknit	In favor	2026-01-29 19:04:36.0 +00:00:00
@muscariello	In favor	2026-01-29 12:42:57.0 +00:00:00
@spetschulatSFDC	In favor	2026-01-29 19:20:21.0 +00:00:00

Non-binding votes (3)

User	Vote	Timestamp
@Tehsmash	In favor	2026-01-28 9:05:01.0 +00:00:00
@herczyn	In favor	2026-01-28 13:48:56.0 +00:00:00
@holtskinner	In favor	2026-01-29 15:49:14.0 +00:00:00

🤖 I have created a release *beep* *boop* --- ## [1.0.0](v0.3.0...v1.0.0) (2026-03-12) ### ⚠ BREAKING CHANGES * **spec:** Combine `TaskPushNotificationConfig` and `PushNotificationConfig` ([#1500](#1500)) * **spec:** remove duplicated ID from the create task push config request ([#1487](#1487)) * **spec:** pluralize configs in `ListTaskPushNotificationConfigs` ([#1486](#1486)) * **spec:** Add LF prefix to the package. ([#1474](#1474)) * **spec:** Switch to non-complex IDs in requests ([#1389](#1389)) * **spec:** Standardize spelling of "canceled" to use American Spelling throughout ([#1283](#1283)) * **spec:** Align enum format with ADR-001 ProtoJSON specification ([#1384](#1384)) * **spec:** Remove redundant `final` field from `TaskStatusUpdateEvent` ([#1308](#1308)) * **spec:** Move `extendedAgentCard` field to `AgentCapabilities` ([#1307](#1307)) * **spec:** Fixes for the last_updated_after field ([#1358](#1358)) * **spec:** modernize oauth 2.0 flows - remove implicit/password, add device code / pkce ([#1303](#1303)) * **spec:** Make "message" field name consistent between protocol bindings ([#1302](#1302)) * **spec:** Remove deprecated fields from a2a.proto for v1.0 release ([#1301](#1301)) * **spec:** Rename `supportsAuthenticatedExtendedCard` to `supportsExtendedAgentCard` ([#1222](#1222)) * **spec:** Remove v1s from a2a url http bindings * **spec:** Large refactor of specification to separate application protocol definition from mapping to transports ### Features * **spec:** Add `tasks/list` method with filtering and pagination to the specification ([0a9f629](0a9f629)) * **spec:** modernize oauth 2.0 flows - remove implicit/password, add device code / pkce ([#1303](#1303)) ([525ff38](525ff38)) * **spec:** Natively Support Multi-tenancy on gRPC through an additional scope field on the request. ([#1195](#1195)) ([cfbce32](cfbce32)), closes [#1148](#1148) * **spec:** Provide ability for SDKs to be backwards compatible. ([#1401](#1401)) ([227e249](227e249)) * **spec:** Remove v1s from a2a url http bindings ([1bd263f](1bd263f)) ### Bug Fixes * Add missing metadata field to Part message in gRPC specification ([#1019](#1019)) ([b3b266d](b3b266d)), closes [#1005](#1005) * Add name field to FilePart protobuf message ([#983](#983)) ([2b7cb6f](2b7cb6f)), closes [#984](#984) * Clarify blocking calls return on interrupted states ([#1403](#1403)) ([0655ff3](0655ff3)) * **doc:** Makes JSON-RPC SendMessage response clearer ([#1241](#1241)) ([5792804](5792804)) * **docs:** Clearer wording around context id. ([#1588](#1588)) ([dec790a](dec790a)) * **grpc:** Fix inconsistent property name between gRPC and JSON-RPC in Message object ([#1100](#1100)) ([2a1f819](2a1f819)) * **grpc:** missing field in gRPC spec - state_transition_history ([#1138](#1138)) ([a2de798](a2de798)), closes [#1139](#1139) * **grpc:** Update `CreateTaskPushNotificationConfig` endpoint to `/v1/{parent=tasks/*/pushNotificationConfigs}` ([#979](#979)) ([911f9b0](911f9b0)) * **proto:** Add icon_url to a2a.proto ([#986](#986)) ([17e7f62](17e7f62)) * **proto:** Adds metadata field to A2A DataPart proto ([#1004](#1004)) ([a8b45dc](a8b45dc)) * Remove unimplemented state_transition_history capability field ([#1396](#1396)) ([c768a44](c768a44)), closes [#1228](#1228) * Restore CreateTaskPushNotificationConfig method naming ([#1402](#1402)) ([d14f410](d14f410)) * Revert "chore(gRPC): Update a2a.proto to include metadata on GetTaskRequest" ([#1000](#1000)) ([e6b8c65](e6b8c65)) * Simplify Part message structure by flattening FilePart and DataPart ([#1411](#1411)) ([bfae8f7](bfae8f7)) * **spec:** Add LF prefix to the package. ([#1474](#1474)) ([a54e809](a54e809)) * **spec:** add metadata to `CancelTaskRequest` ([#1485](#1485)) ([c441b91](c441b91)), closes [#1484](#1484) * **spec:** Added clarification on timestamps in HTTP query params ([#1425](#1425)) ([6292104](6292104)) * **spec:** Added clarifying text around messages and artifacts ([#1424](#1424)) ([b03d141](b03d141)) * **spec:** Adjust field number for `ListTasksRequest.tenant` to prevent missing number ([#1470](#1470)) ([cd16c52](cd16c52)) * **spec:** Clarify contextId behavior when message is sent with taskId but without contextId ([#1309](#1309)) ([a336a5a](a336a5a)) * **spec:** Clarify versioning strategy and client responsibilities in protocol specification ([#1259](#1259)) ([a4afeea](a4afeea)) * **spec:** Fix/1251 clarify authentication scheme ([#1256](#1256)) ([3e6c7db](3e6c7db)) * **spec:** Fixes for the last_updated_after field ([#1358](#1358)) ([0e204bf](0e204bf)) * **spec:** Make "message" field name consistent between protocol bindings ([#1302](#1302)) ([1e5f462](1e5f462)), closes [#1230](#1230) * **spec:** make `history_length` optional ([#1071](#1071)) ([0572953](0572953)) * **spec:** pluralize configs in `ListTaskPushNotificationConfigs` ([#1486](#1486)) ([cf735cb](cf735cb)) * **spec:** Remove config from binding. ([#1587](#1587)) ([010b9cc](010b9cc)) * **spec:** Remove deprecated fields from a2a.proto for v1.0 release ([#1301](#1301)) ([60f83c3](60f83c3)), closes [#1227](#1227) * **spec:** remove duplicated ID from the create task push config request ([#1487](#1487)) ([393898d](393898d)) * **spec:** Remove metadata field from ListTasksRequest ([#1235](#1235)) ([b6ef9ee](b6ef9ee)) * **spec:** Remove reserved and fix tags ordering ([#1494](#1494)) ([1997c9d](1997c9d)) * **spec:** Rename `supportsAuthenticatedExtendedCard` to `supportsExtendedAgentCard` ([#1222](#1222)) ([c196824](c196824)), closes [#1215](#1215) * **spec:** Standardize spelling of "canceled" to use American Spelling throughout ([#1283](#1283)) ([4dd980f](4dd980f)) * **spec:** Suggest Unique Identifier fields to be UUID ([#966](#966)) ([00cf76e](00cf76e)) * **spec:** Switch to non-complex IDs in requests ([#1389](#1389)) ([2596c1c](2596c1c)), closes [#1390](#1390) * **spec:** Update security schemes example ([#1364](#1364)) ([f9a8f5b](f9a8f5b)) * Update the Java tutorials and descriptions ([#1181](#1181)) ([202aa06](202aa06)) ### Documentation * **spec:** Align enum format with ADR-001 ProtoJSON specification ([#1384](#1384)) ([810eaa1](810eaa1)), closes [#1344](#1344) ### Code Refactoring * **spec:** Combine `TaskPushNotificationConfig` and `PushNotificationConfig` ([#1500](#1500)) ([d1ed0da](d1ed0da)) * **spec:** Large refactor of specification to separate application protocol definition from mapping to transports ([b078419](b078419)) * **spec:** Move `extendedAgentCard` field to `AgentCapabilities` ([#1307](#1307)) ([40d6286](40d6286)) * **spec:** Remove redundant `final` field from `TaskStatusUpdateEvent` ([#1308](#1308)) ([5b101cc](5b101cc)) --- This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please). Co-authored-by: Amye Scavarda Perrin <amye@amye.org> Co-authored-by: Holt Skinner <13262395+holtskinner@users.noreply.github.com>

Reintroduce some AgentCard fields + move protocol versions to agent i…

318d617

…nterface.

herczyn requested a review from a team as a code owner January 22, 2026 16:14

gemini-code-assist bot reviewed Jan 22, 2026

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specification/grpc/a2a.proto Outdated Show resolved Hide resolved

holtskinner changed the title ~~[spec]: Provide ability for SDKs to be backwards compatible.~~ feat(spec): Provide ability for SDKs to be backwards compatible. Jan 22, 2026

herczyn added 5 commits January 23, 2026 08:45

Add security and security schemes in the old style to agent card.

ff66c85

Remove deprecated fields from agent card.

553a49e

Add missing reserved.

249d103

Restore removed old auth flows, marked as deprecated.

88469ba

Remove formatting

3fa8613

darrelmiller reviewed Jan 26, 2026

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herczyn added 3 commits January 26, 2026 12:35

Move fields back with name change.

0b5fa8b

Retag field.

20c561c

Merge branch 'a2aproject:main' into backwards_compatibility

cba6e84

herczyn added TSC Review To be reviewed by the Technical Steering Committee P1 Priority for TSC Review labels Jan 26, 2026

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github-project-automation bot moved this to Backlog in TSC Review Jan 26, 2026

Merge branch 'main' into backwards_compatibility

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mikeas1 reviewed Jan 27, 2026

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herczyn added 2 commits January 27, 2026 21:03

Fixes.

7b842a9

Merge remote-tracking branch 'refs/remotes/origin/backwards_compatibi…

80789e7

…lity' into backwards_compatibility

git-vote bot added gitvote gitvote/open labels Jan 27, 2026

Merge branch 'main' into backwards_compatibility

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muscariello self-requested a review January 29, 2026 12:43

muscariello approved these changes Jan 29, 2026

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darrelmiller and others added 2 commits January 29, 2026 11:08

Merge branch 'main' into backwards_compatibility

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Merge branch 'main' into backwards_compatibility

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darrelmiller merged commit 227e249 into a2aproject:main Jan 29, 2026
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github-project-automation bot moved this from Backlog to Done in TSC Review Jan 29, 2026

a2a-bot mentioned this pull request Jan 29, 2026

chore(main): release 1.0.0 #1221

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git-vote bot added gitvote/closed gitvote/passed and removed gitvote/open labels Jan 30, 2026

herczyn deleted the backwards_compatibility branch February 3, 2026 10:23

ishymko mentioned this pull request Feb 9, 2026

docs(spec): Fix whats-new-v1.md #1460

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herczyn commented Jan 27, 2026

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herczyn commented Jan 22, 2026 •

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