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The group.coordinator.rebalance.protocols configuration will be deprecated in Kafka 4.3 and removed in version 5.0, following the same approach as Share Groups. The configuration will be decoupled from feature functionality, meaning it will be accepted but ignored during the transition period. Both New Group Coordinator and Streams will follow the Share Groups model, where functionality is controlled solely by group.version  and streams.version  feature features via kafka-features.sh. During the deprecation period, if users are missing any of default values "classic, consumer, streams", a warning will inform them that this config will be deprecated and they cannot disable a protocol with it in version 5.0.

This eliminates the dual requirement of setting both configuration and feature flags, providing a consistent experience across all coordinator types. Users should use kafka-features.sh for all feature version management , and can safely remove the this configuration from their server.properties files, as it no longer affects feature functionality.

Compatibility, Deprecation, and Migration Plan

Current Status (Kafka 4.2 - Upcoming Release)

Share Groups has already deprecated this configuration and For the group coordinator, after users upgrade, the system will maintain the same version as before the upgrade because feature information is persisted. Users can upgrade using kafka-features.sh without concern for the config value, as it has been decoupled from the feature version. As for Share Groups Both Group Coordinator and Streams rebalance protocol are currently controlled by both the `group.coordinator.rebalance.protocols` configuration and their respective feature flags (`group.version` and `streams.version`).

Deprecation Timeline

Kafka 4.3 (Deprecation Period):

As described in the Proposed Changes, the same applies. Additionally, since neither has reached general access yet, there are no migration concernsif users explicitly set `group.coordinator.rebalance.protocols` with values missing any of the defaults (classic, consumer, streams), users can still disable protocols, but will receive a deprecation warning advising them to either:
- Use the default values (classic, consumer, streams), or
- Remove the configuration

Kafka 5.0 (Removal):
This configuration will be completely removed. Any protocols previously disabled via this configuration will become available, as protocol control will be managed exclusively through feature flags.

Test Plan

This change will be validated through unit and integration tests

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