Splunk Enterprise binary rollback and index bucket compatibility

Index Bucket Versioning during Binary Reversion

Splunk Enterprise allows for the restoration of previous binaries to recover from a failed upgrade. However, the upgrade process often includes migrations to newer index bucket formats on disk to support new features or performance improvements.

While binaries can be reverted to a previous version, the physical format of the index buckets is not automatically downgraded. This creates a potential mismatch where older binaries may be unable to read buckets migrated to a newer version, particularly during major version transitions (e.g., 8.x to 9.x).

What is the documented behavior for the search head and indexers when encountering buckets with a version higher than the current binary? Can these buckets be manually downgraded, or is a full restore from a pre-upgrade backup the only path to data availability?