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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

← All of v2.1.219 Home All releases ←olderv2.1.218 v2.1.220newer→
Claude Code v2.1.219

Opus 5 carries an extra system-prompt block and suppresses subagent nudges

Under the hood
Useful3 Signal0
System Prompt

On some models Claude will stop spinning up subagents or research workflows unless you actually ask for it.

Feature flag
tengu_heron_brook Not enough to say

Nothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.

This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.219: not a boolean we can read

These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.

Read once, for one account on one subscription tier, against v2.1.219. It isn't a statement about your account. What a flag value here can and cannot tell you

What

Models advertising a new capability get an appended prompt block telling the model not to reach for subagents or research workflows unprompted, and the matching steering nudge is turned off for them.

Details
  • gated on the opus_5_prompt_bundle capability, with a remote kill-flag checked inside the capability test (fallback: not killed)
  • the appended block reads "Do not call the AgentTool unless the user requested it" and "Do not use workflows or deep-research unless the user requested it"
  • application is logged as tengu_heron_brook_applied with fromClientData: !1
  • the tengu_heron_brook string flag still overrides
  • the same capability check feeds the "thistle grebe" steering resolver with a new "model" source returning "no_nudges", suppressing the delegate-to-subagents steering text
Evidence

Do not call the AgentTool unless the user requested it

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.219 →