tengu_lucky_cerf
A Claude Code feature flag, read out of the shipped bundle. It was in the build from v2.1.271 and was gone by v2.1.307.
New guidance nudges Claude to weigh the real cost before spawning a subagent
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.271.
In the changelogs
3Releases whose published page names tengu_lucky_cerf.
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v2.1.307
Startup retries when your sign-in token is still being refreshed
If organization settings can't load because your sign-in token is mid-refresh, Claude Code retries once and gives a clearer message if it still fails
gate cited by this entry
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v2.1.307
Runs blocked while a sign-in token refreshes get one retry
When a policy check is blocked because a sign-in token was still refreshing, Claude Code now retries once within a time limit
gate cited by this entry
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v2.1.271
New model-pattern-gated nudge encouraging judicious subagent delegation ('lucky_cerf')
New guidance nudges Claude to weigh the real cost before spawning a subagent
gate cited by this entry
Gate readings
2| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.307 read on another version | Not enough to say | no value returned | no value returned | not a boolean we can read |
| v2.1.271 read on another version | Not enough to say | no value returned | no value returned | not a boolean we can read |
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.
Flag server, over time
8| Read as | Reading | From | Until | Version installed |
|---|---|---|---|---|
| this account | no longer carried | 2026-11-04T22:45:05Z | 2026-11-04T22:45:05Z | v2.1.318 |
| anonymous | no longer carried | 2026-11-04T22:15:05Z | 2026-11-04T22:15:05Z | v2.1.318 |
| this account | ["claude-opus-5","claude-fable-5","claude-fable-5-1","claude-mythos-5","claude-mythos-5-1","claude-sonnet-5-5","claude-haiku-5-5"] | 2026-10-08T05:20:05Z | 2026-11-04T22:15:05Z | v2.1.293 to v2.1.318 |
| anonymous | ["claude-opus-5","claude-fable-5","claude-fable-5-1","claude-mythos-5","claude-mythos-5-1","claude-sonnet-5-5","claude-haiku-5-5"] | 2026-10-17T05:30:04Z | 2026-11-04T21:05:05Z | v2.1.302 to v2.1.318 |
| anonymous | no longer carried | 2026-10-17T05:25:57Z | 2026-10-17T05:25:57Z | v2.1.302 |
| anonymous | ["claude-opus-5","claude-fable-5","claude-fable-5-1","claude-mythos-5","claude-mythos-5-1","claude-sonnet-5-5","claude-haiku-5-5"] | 2026-10-08T05:15:05Z | 2026-10-17T05:10:04Z | v2.1.293 to v2.1.302 |
| this account | [] | 2026-09-11T21:35:04Z | 2026-10-08T05:15:05Z | v2.1.269 to v2.1.293 |
| anonymous | [] | 2026-09-11T21:35:04Z | 2026-10-08T05:10:04Z | v2.1.269 to v2.1.293 |
One row per unbroken stretch of one reading, newest first, from snapshots taken every twenty-five minutes or so. No longer carried is not off: it means the flag server stopped returning the gate at all, which is what a retired experiment looks like. The version column is what was installed when the reading was taken, not what caused it.
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
45One 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.