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whilst it's ideal to upgrade your brokers and clients together as part of standard maintenance, it may be desirable to upgrade clients only.
The bi-directional compatibility improvements were made through the following KIPs:
KIP-35 - Retrieving protocol version
KIP-97: Improved Kafka Client RPC Compatibility Policy
If version <0.10.1.x is in use, you have to upgrade it to at least 0.10.1 (using existing upgrade/rolling upgrade guideline).
https://www.confluent.io/blog/upgrading-apache-kafka-clients-just-got-easier
To refer to official upgrade docs - https://kafka.apache.org/documentation/#ecosystem