tengu_radiant_island
A Claude Code feature flag, read out of the shipped bundle. It was in the build from v2.1.240 and was gone by v2.1.263.
A one-time prompt offering to switch your default effort to medium exists but has no text.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.240.
In the changelogs
7Releases whose published page names tengu_radiant_island.
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v2.1.263
Effort-medium nudge generalized to per-model remote-config gates
The effort-downgrade nudge was rebuilt to support multiple models, each hidden behind its own remote switch.
found in this entry's text, gate cited by this entry
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v2.1.263
Effort-medium nudge generalized to multiple models and effort levels
The effort-downgrade nudge now works per model instead of just one, but each model needs its own flag turned on.
gate cited by this entry
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v2.1.263
Effort-medium-nudge remote config now validated for effort-level ordering, plus fromEffort/toEffort treated as invalid fields
Server-served effort nudge text is now rejected outright if its effort-level ordering looks invalid.
gate cited by this entry
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v2.1.263
Effort nudge confirm dialog supports templated copy and an optional warning banner
The effort nudge dialog can now fill in the model and levels by name and show a warning banner, once enabled.
gate cited by this entry
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v2.1.251
One-time nudge when reasoning effort is set to high
A one-time dialog may suggest lowering your reasoning effort, only if the server supplies wording.
gate cited by this entry, found in this entry's text
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v2.1.240
"Switch your default effort to medium?" prompt, complete but with no text to show
A one-time prompt offering to switch your default effort to medium exists but has no text.
gate cited by this entry, found in this entry's text
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v2.1.240
Telemetry for the effort nudge
Two events would record the effort prompt and your answer, but it never shows.
gate cited by this entry, found in this entry's text
Gate readings
3| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.263 read on another version | Not enough to say | no value returned | no value returned | no gate table built for this version |
| v2.1.251 | Not enough to say | no value returned | no value returned | not a boolean we can read |
| v2.1.240 | 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
14| Read as | Reading | From | Until | Version installed |
|---|---|---|---|---|
| anonymous | [] | 2026-10-17T05:30:04Z | 2026-10-22T06:25:04Z | v2.1.302 to v2.1.308 |
| this account | [] | 2026-09-10T21:47:12Z | 2026-10-22T06:25:04Z | v2.1.268 to v2.1.308 |
| anonymous | no longer carried | 2026-10-17T05:25:57Z | 2026-10-17T05:25:57Z | v2.1.302 |
| anonymous | [] | 2026-08-21T22:05:05Z | 2026-10-17T05:10:04Z | v2.1.233 to v2.1.302 |
| this account | no longer carried | 2026-09-10T21:46:45Z | 2026-09-10T21:46:45Z | v2.1.268 |
| this account | [] | 2026-09-08T20:36:15Z | 2026-09-10T17:40:05Z | v2.1.263 to v2.1.267 |
| this account | no longer carried | 2026-09-08T20:34:58Z | 2026-09-08T20:34:58Z | v2.1.265 |
| this account | [] | 2026-09-06T02:40:05Z | 2026-09-08T18:45:05Z | v2.1.261 to v2.1.263 |
| this account | no longer carried | 2026-09-06T02:36:19Z | 2026-09-06T02:36:19Z | v2.1.263 |
| this account | [] | 2026-08-21T22:05:05Z | 2026-09-06T01:55:04Z | v2.1.233 to v2.1.261 |
| anonymous | off | 2026-08-19T04:25:04Z | 2026-08-21T21:40:04Z | v2.1.233 |
| this account | off | 2026-08-14T22:10:05Z | 2026-08-21T21:40:04Z | v2.1.232 to v2.1.233 |
| anonymous | no longer carried | 2026-08-19T04:20:14Z | 2026-08-19T04:20:14Z | v2.1.233 |
| anonymous | off | 2026-08-14T22:10:05Z | 2026-08-19T03:45:04Z | v2.1.232 to v2.1.233 |
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
2The earliest release whose published evidence quoted tengu_radiant_island was v2.1.263, 6 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
58One 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.