When the setting is enabled, an automatic compaction is shown as a single quiet divider: “Compacting” while it runs and “Compacted” after it finishes.
A completed divider can be clicked to reveal the compaction summary and its token usage. The implementation waits 400 ms before showing an in-progress state; compactions completed inside that window show only the finished state. Reduced-motion mode keeps the lines static and crossfades the label.
The change is gated by experimental.background_compaction. With that flag off, the existing automatic-compaction presentation remains in place. Manual /compact operations and failed compactions also retain their existing display. The pull request includes component and end-to-end test results.
The source describes a merged UI change for the experimental path, not a stable-release version, general availability, or measured effects on compaction quality, latency, or token consumption.