{"name":"tengu_heron_brook","slug":"tengu-heron-brook","family":"flag","title":"Feature flags","noun":"feature flag","description":"On some models Claude will stop spinning up subagents or research workflows unless you actually ask for it.","description_source":"entry","described_by":{"version":"2.1.219","anchor":"opus-5-carries-an-extra-system-prompt-block-and-suppresses-s"},"presence":{"first_seen":"2.1.150","removed_in":null,"in_current_build":true,"newest_mined":"2.1.308","builds":137,"mined_builds":149,"first_cited":null},"aliases":[],"entries":[{"version":"2.1.257","anchor":"tengu-heron-brook-telemetry-now-also-reports-client-data-pro","heading":"tengu_heron_brook telemetry now also reports client-data-provided values consistently","line":"A flag's applied-event telemetry is now emitted once from the caller instead of at duplicated call sites.","released_at":"2026-09-01 17:15:33","reason":"found in this entry's text, gate cited by this entry"},{"version":"2.1.219","anchor":"opus-5-carries-an-extra-system-prompt-block-and-suppresses-s","heading":"Opus 5 carries an extra system-prompt block and suppresses subagent nudges","line":"On some models Claude will stop spinning up subagents or research workflows unless you actually ask for it.","released_at":"2026-07-24 16:11:49","reason":"gate cited by this entry, found in this entry's text"},{"version":"2.1.219","anchor":"opus-5-gets-an-extra-system-prompt-instruction-restricting-a","heading":"Opus 5 gets an extra system-prompt instruction restricting AgentTool, workflows and deep-research","line":"On Opus 5, Claude is told not to spawn subagents, workflows or deep research unless you ask.","released_at":"2026-07-24 16:11:49","reason":"gate cited by this entry, found in this entry's text"}],"entries_total":3,"docs":[],"docs_total":0,"gates":[{"version":"2.1.257","state":"unknown","account":null,"baseline":null,"code_default":null},{"version":"2.1.219","state":"unknown","account":null,"baseline":null,"code_default":null}],"related":[{"name":"tengu_heron_brook_applied","slug":"tengu-heron-brook-applied","description":"On some models Claude will stop spinning up subagents or research workflows unless you actually ask for it."},{"name":"tengu_heron_tallow","slug":"tengu-heron-tallow","description":"Default `false`. Changes the hint added when the model calls a tool that is not available: for a known tool it reads `<tool> is disabled for this session, in subagents as well as here.` instead of `exists but is not enabled in this context`, and for Glob or Grep when Bash is also unavailable it reads `<tool> is disabled for this session.` `CLAUDE_CODE_HERON_TALLOW` turns on the same wording."}],"url":"https:\/\/changelogs.core-directive.com\/reference\/flag\/tengu-heron-brook","family_url":"https:\/\/changelogs.core-directive.com\/reference\/flag.json"}