Some of the notable changes include:
Bug Fix
Tag and version numbers will now match: v0.4.0 and v0.4.0
Enhancements
DelegationHistory now uses a block based frequency instead of seconds.
When a delegation happens the history is aggregated at the daily level.
Added compoundModuleEnabled parameter to the compound module to disable local compounding via governance.
Full changelog can be viewed here v0.3.0...v0.4.0