tengu_bg_session_id_taken
A Claude Code feature flag, read out of the shipped bundle. No mined inventory carries it: everything below comes from what this site has written about it.
Background sessions that hit an already-claimed session id now fail with a clear dimmed notice.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.248.
In the changelogs
1Releases whose published page names tengu_bg_session_id_taken.
-
v2.1.248
Background sessions report a taken session id as a distinct crash
Background sessions that hit an already-claimed session id now fail with a clear dimmed notice.
gate cited by this entry, found in this entry's text
Gate readings
0No release here has a gate table behind it for this flag. Most published releases have none at all: the readings exist only for versions the pipeline captured flag state on.
First cited
1The earliest release whose published evidence quoted tengu_bg_session_id_taken was v2.1.248, 27 Aug 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
0The miner has never read a build containing this name. It is here because a changelog entry of ours names it, which is evidence that it existed and not evidence of which releases carried it. The inventory starts at v2.1.138 and everything older than that was 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.