What it is
New gate tengu_tidy_fern can add an extra value into how user messages are built
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.274.
Presence across releases
1Build by build
5One 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.
First cited
1The earliest release whose published evidence quoted tengu_tidy_fern was v2.1.274, 16 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 above.
Gate readings
1| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.274 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.
Names beside it
Every feature flag in the inventory starting tengu, up to twelve of them.
tengu_1p_event_batch_configNo description from anybody. never mined
tengu_account_plugins_sync_enabledPlugins you enabled on claude.ai can be pulled to your machine, but only your account server can enable it. never mined
tengu_account_skills_sync_enabledAccount skills-sync eligibility logic generalized into a reusable descriptor v2.1.234
tengu_adopt_claimStale adopted session claims now return their data marked stale instead of being discarded never mined
tengu_adopt_linkAdopting an agent's transcript now hard-links the file, copying only when linking is impossible. never mined
tengu_adopt_relinkOn startup, subagent transcripts stored as symlinks are converted to hard links or copies. never mined
tengu_advisor_unknown_contentAdvisor output you couldn't see now shows an error or a clear "declined to advise" message. never mined
tengu_agent_frontmatter_mode_widening_carry_ignoredAn agent definition's permissionMode can no longer widen the mode inherited from its parent context. never mined
tengu_agent_hooks_origin_untrustedAgents in untrusted folders can no longer define inline MCP servers; trust the project to allow it. never mined
tengu_agent_list_attachNo description from anybody. v2.1.138
tengu_agent_proxy_download_queueDownload backlog on the agent proxy is now reported as a telemetry event. never mined
tengu_agent_proxy_failure_noteProxy connection failures during a command are summarised afterwards, grouped by host, with a curl pointer. never mined
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.