# Limitations

- Kafka 4.0+ only.
- No brokers before Kafka 4.0.
- No classic consumer group protocol.
- No classic `JoinGroup` / `SyncGroup` / classic heartbeat membership.
- No older transaction protocol fallback.
- No OAuthBearer support.
- No GSSAPI/Kerberos support.
- No AWS/MSK IAM support.
- Transaction support targets transaction protocol v2.
- Consumer support targets modern consumer groups.
- Share consumption targets Kafka share groups.
- Public errors are still being tightened for release.
- Fault and stress coverage is still expanding before release candidate status.

## Why These Limits Exist

- kafkit-client is designed around the Kafka 4.0+ protocol surface.
- The crate avoids carrying old broker compatibility branches during the first release phase.
- The supported path is smaller, easier to test, and clearer for production users.
- Classic groups and transaction fallback paths can be reconsidered later if users need them.

## Practical Impact

- Use Kafka 4.0+ brokers.
- Use KRaft clusters.
- Use modern consumer groups for partition ownership.
- Use share groups for work sharing.
- Use transaction protocol v2 for transactional producers.
- Keep older client libraries for older broker fleets until those brokers are upgraded.
