A Claude Code environment variable, read out of the shipped bundle.
It has been in the build since v2.1.138, including the newest one read.
Set to 1 to disable 1M context window support. When set, 1M model variants are unavailable in the model picker, and Claude Code holds sessions on models with a native 1M window, such as Sonnet 5.5 and the Fable models, to a 200K window; see Extended context for how the hold is enforced. Useful for enterprise environments with compliance requirements. For its role in correcting the window for an unrecognized [1m] model ID, see Correct the window for a gateway or custom model ID
If your 1M-context disable flag has no effect on your model, startup now tells you and points at the real setting.
named in this entry, found in this entry's text
First cited
4
The earliest release whose published evidence quoted CLAUDE_CODE_DISABLE_1M_CONTEXT was v2.1.223, 5 Aug 2026. That is the oldest release this project wrote about it, so it is a floor on the name's age and not the release that introduced it. It is not a presence reading: which builds carried the name is the table below.
ReleaseDateThe span that was quoted
v2.1.2235 Aug 2026CLAUDE_CODE_DISABLE_1M_CONTEXT is set, but the
v2.1.2658 Sep 20261M context is turned off here (CLAUDE_CODE_DISABLE_1M_CONTEXT is set)
v2.1.2658 Sep 20261M context is turned off here (CLAUDE_CODE_DISABLE_1M_CONTEXT is set), so '${n}' isn't available. Run /model ${s} instead.
Presence across releases
1
BuildsHow manyDatesReading
v2.1.138 – v2.1.308149 builds9 May 2026 → 22 Oct 2026 ◆in the build
Build by build
149
One row per release since the first build this name was read out of. Absent means the build was read and the name was not in it, never mined means no bundle for that release was ever archived, and a declared type or a default is only ever what that release's own bundle stated.
v2.1.29914 Oct 2026·presentverdict: present · bool
v2.1.30014 Oct 2026·presentverdict: present · bool
v2.1.30115 Oct 2026·presentverdict: present · bool
v2.1.30216 Oct 2026·presentverdict: present · bool
v2.1.30318 Oct 2026·presentverdict: present · bool
v2.1.30419 Oct 2026·presentverdict: present · bool
v2.1.30520 Oct 2026·presentverdict: present · bool
v2.1.30621 Oct 2026·presentverdict: present · bool
v2.1.30721 Oct 2026·presentverdict: present · bool
v2.1.30822 Oct 2026·presentverdict: present · bool
Read out of the published npm bundle release by release, and out of Anthropic's own documentation as this site captured it. Nothing on this page is a description anybody here wrote about what the environment variable does. All environment variables.
