tengu_heron_brook_applied
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.
On some models Claude will stop spinning up subagents or research workflows unless you actually ask for it.
Not Anthropic's. This is the line from the earliest changelog entry here that named it, v2.1.219.
In the changelogs
3Releases whose published page names tengu_heron_brook_applied.
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v2.1.257
tengu_heron_brook telemetry now also reports client-data-provided values consistently
A flag's applied-event telemetry is now emitted once from the caller instead of at duplicated call sites.
found in this entry's text, gate cited by this entry
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v2.1.219
Opus 5 carries an extra system-prompt block and suppresses subagent nudges
On some models Claude will stop spinning up subagents or research workflows unless you actually ask for it.
gate cited by this entry, found in this entry's text
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v2.1.219
Opus 5 gets an extra system-prompt instruction restricting AgentTool, workflows and deep-research
On Opus 5, Claude is told not to spawn subagents, workflows or deep research unless you ask.
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_heron_brook_applied was v2.1.257, 1 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
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.