You'll noticeTier: how much it should matter to you
2Useful: my rating, 1 to 5
1Signal: worth watching, 1 to 5
CompactionArea: what it touches
ImprovementsKind: in v2.1.312,
ImprovementsSection of the release
Unclear It is not clear where the ceiling comes from or who sets it, so it is unclear whose values are affected.
What
Auto-compact is when Claude Code summarises older parts of a conversation to free up room, and the auto-compact window is how large the conversation can grow, in tokens, before that happens. Tokens are the small chunks of text the model counts.
CLAUDE_CODE_AUTO_COMPACT_WINDOW is an environment variable that sets this window. Before, a value set this way skipped the ceiling check that other ways of setting the window go through. Now, when a ceiling applies and your value is above it, the window is reduced to the ceiling, and Claude Code reports the result as coming from settings rather than from the environment variable.
Why
If you set CLAUDE_CODE_AUTO_COMPACT_WINDOW above the ceiling, you will now get a smaller window than before, so compaction will start earlier than your value suggests.
How sure we are
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubtIt is not clear where the ceiling comes from or who sets it, so it is unclear whose values are affected.
Anthropic's release notes agreeChanged a subagent's autoCompactWindow to lower the window set by CLAUDE_CODE_AUTO_COMPACT_WINDOW, where it had no effect before; it still…
