tengu_mossy_crown
A Claude Code feature flag, read out of the shipped bundle. It has been in the build since v2.1.292, including the newest one read.
A new accessFallbackModels setting lists models Claude Code may fall back to when the main model can't be used
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.292.
In the changelogs
2Releases whose published page names tengu_mossy_crown.
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v2.1.299
Model switch list is now filtered by the model you are using
The list of models a session may switch to now comes from a configuration whose entries apply only to particular current models
gate cited by this entry
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v2.1.292
Backup model list for when the main model is unavailable
A new accessFallbackModels setting lists models Claude Code may fall back to when the main model can't be used
gate cited by this entry
Gate readings
2| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.299 read on another version | Not enough to say | no value returned | no value returned | on |
| v2.1.292 read on another version | Not enough to say | no value returned | no value returned | on |
Two arms, because they disagree: this account is the one account this site reads and anonymous is a baseline with no identity attached. A reading says nothing about your account, and off cannot rule out a rollout both readings sit outside of. What these readings can and cannot show.
First cited
1The earliest release whose published evidence quoted tengu_mossy_crown was v2.1.299, 14 Oct 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
1Build by build
15One 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.