tengu_plum_heron
A Claude Code feature flag, read out of the shipped bundle. It was in the build from v2.1.286 and was gone by v2.1.287.
Default { off: true }. Config object for a notice about a newer model in the same family as the model saved in your user settings (state keys savedModelSuccessorShown and savedModelSuccessorAnswered). The notice is suppressed when off is true, when the model's family is turned off in families (falling back to a built-in per-family default), after it has been answered, after maxViews showings, or when it was shown more recently than minDaysApart allows. The object also accepts lead, text, action and done strings; a value that fails validation counts as { off: true }.
Not Anthropic's. Written by Claude Opus 5.5 from reading the v2.1.286 bundle, and it can be wrong.
In the changelogs
0No changelog entry here has ever named it. That is a statement about what has been written, not about the name: it has been in the build since v2.1.286 without anybody writing a line about it.
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
1The earliest release whose published evidence quoted tengu_plum_heron was v2.1.286, 30 Sep 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.
Presence across releases
2Build by build
21One 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.