Glossary Compaction
Compaction
Also known as:
context compactionAgenticAI
Definition
The harness summarizing the older part of a context window to make room — what the agent keeps is the summary, not the material
It happens on its own when the window fills. Facts that were established early survive only as far as the summary carried them, which is why a decision worth keeping goes into a file, a commit message or a memory, not the conversation.
The felt symptom is an agent re-deriving something it already knew, or losing a constraint it was given an hour ago. The remedy is the same as for a session ending: write it down where the next reader will look. The Dictionary of AI Coding has a longer treatment.