Compaction
Also called /compact, compress, auto-compact
When a coding agent replaces the earlier part of a long session with a summary, to make room in its context window.
A coding agent re-sends the whole session with every request, and the session has a ceiling: the context window. When it gets close, the agent swaps the older part for a summary and carries on.
The summary keeps the main thread and drops detail, so a decision you settled in passing can vanish with it. Anything that must outlast the session belongs in a file: the instructions file for rules, a progress note for a long task. Between unrelated tasks, clearing is usually the better move.
For example
3 hours into a migration, the session compacts. Afterwards the agent no longer recalls that the old column was to be kept for a week.
Put it to use
Where you'll meet compaction in ChatGPT, Gemini and Claude, how to use it there, and the mix-up most people make.
Daily Bytes Plus is in the Android app.