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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 gets an extra system-prompt instruction restricting AgentTool, workflows and deep-research

You'll notice
Useful4 Signal0
System Prompt Notable

On Opus 5, Claude is told not to spawn subagents, workflows or deep research unless you ask.

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.

tengu_fennel_godwit Off in both readings

The flag server returned off for the account this site reads and for the anonymous baseline. A reading of off cannot rule out a rollout these two readings sit outside of.

This account: off · anonymous baseline: off · 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 carrying the opus-5 prompt bundle now receive a built-in instruction telling Claude not to spawn subagents or run workflows and deep-research unless the user asked for it.

Details
  • the tengu_heron_brook injection previously came only from client data or the remote flag string; it now falls back to a built-in two-line block
  • the fallback applies when the model carries the opus_5_prompt_bundle capability
  • killswitch is tengu_fennel_godwit
  • the applied event still fires as tengu_heron_brook_applied with fromClientData: !1 on this path
Evidence

Do not use workflows or deep-research 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 →