tengu_iterative_lightning
A Claude Code feature flag, read out of the shipped bundle. It has been in the build since v2.1.299, including the newest one read.
When a session is resumed, Claude can now be warned about tool calls that were lost, but only when this is switched on remotely
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.299.
In the changelogs
2Releases whose published page names tengu_iterative_lightning.
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v2.1.302
Lost tool call warning now explains that the session restarted
After a restart, Claude can get an urgent reminder that the session restarted mid-turn and its tool calls may not have run, if switched on remotely
gate cited by this entry
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v2.1.299
Resumed sessions can warn Claude about lost tool calls
When a session is resumed, Claude can now be warned about tool calls that were lost, but only when this is switched on remotely
gate cited by this entry
Gate readings
2| Release | Resolved | This account | Anonymous | Compiled default |
|---|---|---|---|---|
| v2.1.302 read on another version | Off in both readings | off | off | off |
| v2.1.299 read on another version | Not enough to say | no value returned | no value returned | off |
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 | off | 2026-10-17T05:30:04Z | 2026-10-22T07:55:04Z | v2.1.302 to v2.1.308 |
| this account | off | 2026-10-14T07:05:04Z | 2026-10-22T07:55:04Z | 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 | off | 2026-10-14T06:40:04Z | 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_iterative_lightning was v2.1.299, 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
10One 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.