...

After consumer receives OffsetFetchResponse, it remembers the leader_epoch for each partition it needs to consume. Then the consumer needs to refresh metadata until the leader_epoch in the cached metadata >= the leader_epoch in OffsetFetchResponse for all partitions it wants to consume. Note that these logic are all hidden from user and the leader_epoch will not be exposed to user via consumer's public API (e.g. OffsetAndMetadata).

For existing version of the offset topic, leader_epoch will not be available in the value of the offset topic. We will use leader_epoch = -1 to indicate the missing leader_epoch. In this case leader_epoch in any MetadataResponse will be larger than the leader_epoch = -1 and the consumer behavior will be the same as it is now.

Compatibility, Deprecation, and Migration Plan

...