What
Auto-compact is when Claude Code summarises the conversation so far to free up room in the model's memory. The auto-compact window sets how full that memory can get, in tokens, before this happens. CLAUDE_CODE_AUTO_COMPACT_WINDOW is an environment variable, a value set in your shell, that sets this window. This release changes how it is read and shown:
- The value is read by a new parser. It accepts shorthand such as
200kor1M, and a bare number between 100 and 1000 is treated as thousands. - Values that are too small or too large are brought up to the minimum or down to the maximum, with a warning in the log or in headless output.
- A value that cannot be read at all is ignored, with the message that it "isn't a usable size, so Claude Code ignores it." Before, an invalid value was dropped without a visible warning.
- At startup in interactive mode, the variable is checked and a warning is raised if needed.
- The auto-compact window entry in
/confignow shows an extra warning-coloured line built from the environment variable. Its exact wording was not read. Before, the only extra line was "Auto-compact is currently disabled (see /config)".
Why
A mistyped window size now produces a warning instead of quietly having no effect, and the settings screen points out when the environment variable is in play.
Names in the bundleCLAUDE_CODE_AUTO_COMPACT_WINDOW
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed since
Anthropic's documentation has since written up CLAUDE_CODE_AUTO_COMPACT_WINDOW, on Error reference.
| `CLAUDE_CODE_AUTO_COMPACT_WINDOW="<value>" reads as <N> tokens, so Claude Code treats it as the 100k minimum` | [Values and warnings for `CLAUDE_CODE_AUTO_COMPACT_WINDOW`](/docs/en/model-config#claude_code_auto_compact_window-values) |errors see the edit
Two sources agreeTwo things we can check say the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up CLAUDE_CODE_AUTO_COMPACT_WINDOW, on Error reference.
Anthropic's release notes agree
Fixed CLAUDE_CODE_AUTO_COMPACT_WINDOW=200k silently setting a 100K window: the variable now accepts k and M suffixes like --autocompact, and…