tengu_tranquil_fern
A Claude Code feature flag, read out of the shipped bundle. It was in the build from v2.1.239 and was gone by v2.1.300.
Resuming a session that was in plan mode now puts you back in plan mode.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.239.
In the changelogs
4Releases whose published page names tengu_tranquil_fern.
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v2.1.275
tengu_repl_mcp_error_throw gate appears renamed to tengu_tranquil_fern
The gate behind MCP error-throwing now reads under the name tengu_tranquil_fern instead of tengu_repl_mcp_error_throw
gate cited by this entry, found in this entry's text, named in this entry
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v2.1.248
Flag values can be pinned for the life of the process, and a new pinned flag appears
Some feature flags now stay fixed for the whole session, including a new one that is on.
gate cited by this entry, found in this entry's text
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v2.1.246
Plan mode can be restored by reading the transcript
Resuming a session can now re-enter plan mode by reading your transcript, and this is on by default.
gate cited by this entry, found in this entry's text
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v2.1.239
Resuming a session that was in plan mode puts you back in plan mode
Resuming a session that was in plan mode now puts you back in plan mode.
gate cited by this entry, found in this entry's text
Gate readings
1| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.275 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_tranquil_fern was v2.1.275, 17 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
4Build by build
59One 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.