A Claude Code feature flag, read out of the shipped bundle.
It was in the build from v2.1.138 and was gone by v2.1.268.
Default {}. Object of default file reading limits used by the Read tool and other file reads: maxSizeBytes (default 262144), maxTokens (default 25000; CLAUDE_CODE_FILE_READ_MAX_OUTPUT_TOKENS above 0 takes precedence), includeMaxSizeInPrompt (when true, the Read prompt says files larger than the size limit return an error) and targetedRangeNudge (when true, the Read prompt tells the model to read only the part of a file it needs instead of recommending reading the whole file). Numbers that are not positive and finite fall back to the defaults, and the result is cached for the session.
Not Anthropic's. Written by Claude Opus 5.5 from reading the v2.1.267 bundle, and it can be wrong.
First seen v2.1.138 9 May 2026
Last seen v2.1.267 9 Sep 2026, gone by v2.1.268
Builds106 / 149on this box, as of v2.1.308
Written about v2.1.75 first named in a changelog, 13 Mar 2026
v2.1.138in the build not in the build never minedv2.1.308
In the changelogs
1
Releases whose published page names tengu_amber_wren.
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
12
Read as
Reading
From
Until
Version installed
anonymous
{"maxTokens":25000,"targetedRangeNudge":true}
2026-10-17T05:30:04Z
2026-10-22T05:30:05Z
v2.1.302 to v2.1.308
this account
{"maxTokens":25000,"targetedRangeNudge":true}
2026-09-10T21:47:12Z
2026-10-22T05:30:05Z
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
{"maxTokens":25000,"targetedRangeNudge":true}
2026-08-19T04:25:04Z
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
{"maxTokens":25000,"targetedRangeNudge":true}
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
{"maxTokens":25000,"targetedRangeNudge":true}
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
{"maxTokens":25000,"targetedRangeNudge":true}
2026-08-14T22:10:05Z
2026-09-06T01:55:04Z
v2.1.232 to v2.1.261
anonymous
no longer carried
2026-08-19T04:20:14Z
2026-08-19T04:20:14Z
v2.1.233
anonymous
{"maxTokens":25000,"targetedRangeNudge":true}
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
1
The earliest release whose published evidence quoted tengu_amber_wren was v2.1.75, 13 Mar 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.
v2.1.138 – v2.1.24193 builds9 May 2026 → 22 Aug 2026 ◆in the build
v2.1.242 – v2.1.2475 builds24 Aug 2026 → 26 Aug 2026 ○not in the build
v2.1.248 – v2.1.26713 builds27 Aug 2026 → 9 Sep 2026 ◆in the build
v2.1.268 – v2.1.30838 builds10 Sep 2026 → 22 Oct 2026 ○not in the build
Build by build
149
One 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.
BuildDateStateThe record behind it
v2.1.1389 May 2026·presentverdict: present · default object
v2.1.13911 May 2026·presentverdict: present · default object
v2.1.14012 May 2026·presentverdict: present · default object
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.
