Compaction

Claude Code Compacts Idle Chats, and Has Since September

On 14 October the Claude Code 2.1.299 changelog documented idle compaction: a 200K+ token terminal conversation left idle for about 54 minutes is summarized before its one-hour prompt cache expires. The behavior had been live since 2.1.286 on 30 September through a server-side flag, the idleCompaction opt-out shipped in 2.1.290 on 5 October without a changelog line and was documented by a user reading the binary, and the /config row came in 2.1.302 on 16 October. At Opus 5.5 list prices it trades a $1.60 cold rebuild of a 200,000-token prefix for a $0.04 cache read and a roughly $0.40 summary, runs only on the one-hour TTL that subscribers get within plan usage, summarizes away path-scoped rules, nested CLAUDE.md files and hook-injected context, and records itself as trigger auto, so a PreCompact hook can only tell it from a context-limit compaction by checking the transcript's age.