tengu_larch_cistern
A Claude Code feature flag, read out of the shipped bundle. It was in the build from v2.1.257 and was gone by v2.1.260.
Default false. When on, the system prompt gets an overcorrection section headed # Corrections, telling the model to avoid unnecessary self-correction, to correct an earlier statement only when the error would change the user's code, conclusions or decisions, and not to treat a follow-up question as a sign it was wrong. The section is also added when CLAUDE_CODE_LARCH_CISTERN is set, when the Opus 5 prompt bundle applies (unless tengu_fennel_godwit is on), or when the client data key of this name is true.
Not Anthropic's. Written by Claude Opus 5.5 from reading the v2.1.259 bundle, and it can be wrong.
In the changelogs
1Releases whose published page names tengu_larch_cistern.
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v2.1.217
Four New Unnamed Feature Flags [In Development]
gate cited by this entry, found in this entry's text
Gate readings
0No release here has a gate table behind it for this flag. Most published releases have none at all: the readings exist only for versions the pipeline captured flag state on.
First cited
0No release's published evidence quotes this name. The ledger indexes the Evidence lines of every changelog on this site, so this says nobody here has ever quoted it; it says nothing about how old the name is.
Presence across releases
2Build by build
47One 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.
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 feature flag does. All feature flags.