tengu_binary_music
A Claude Code feature flag, read out of the shipped bundle. It has been in the build since v2.1.300, including the newest one read.
Users with a one-million-token context can be offered a choice of when auto-compact kicks in, from 300k to 900k tokens
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.300.
In the changelogs
2Releases whose published page names tengu_binary_music.
-
v2.1.301
Claude Code can offer to compact long conversations sooner
A new dialog can suggest auto-compacting at a smaller size on 1M-context models, and saves the lower size to your user settings if you accept
gate cited by this entry
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v2.1.300
Offer to choose an auto-compact size for 1M-context sessions
Users with a one-million-token context can be offered a choice of when auto-compact kicks in, from 300k to 900k tokens
found in this entry's text
Gate readings
1| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.301 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
4| 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 | [] | 2026-10-14T16:35:04Z | 2026-10-22T06:25:04Z | v2.1.299 to v2.1.308 |
| anonymous | no longer carried | 2026-10-17T05:25:57Z | 2026-10-17T05:25:57Z | v2.1.302 |
| anonymous | [] | 2026-10-14T15:55:04Z | 2026-10-17T05:10:04Z | v2.1.299 to v2.1.302 |
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
1The earliest release whose published evidence quoted tengu_binary_music was v2.1.300, 14 Oct 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
1Build by build
9One 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.