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this post was submitted on 26 Jul 2026<br>1 point (100% upvoted)<br>shortlink:

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Claude Code has a hardcoded instruction telling Opus 5 not to use subagentsBug Report (self.ClaudeCode)<br>submitted 10 minutes ago * by jetsetter

Anthropic has a two line system prompt that was being remotely injected but now is a part of the compiled binary in 2.1.219, and 220 targeting only Opus 5:

Do not call the AgentTool unless the user requested it<br>Do not use workflows or deep-research unless the user requested it

This disproportionately affects skills that are designed to use subagents. The prompt is enough for Opus 5 to choose to run agents' work inline (or silently not perform their work) and produces output that looks like a normal run.

For example, I found one session that ran a self-audit non-blind because it couldn't spawn the auditor agent. Opus noticed this was a problem but let it slide undermining the entire point of the independent audit of its work.

I searched issues and found someone already filed it with binary analysis: anthropics/claude-code#80988 .

I believe that my reliance on skills that expect and prescribe routine use of agent delegation has been a contributor to the poor quality of output I've gotten from Opus 5 so far.

It may be affecting you too.

You can check this out yourself, ask Claude:

I want you to help me analyze the file ~/.claude.json

Focus specifically on heron brook

How might that may affect the behavior of my skills?

If you want to check how big of an impact it has had on your use so far, ask claude:

Claude Code 2.1.219+ injects a system-prompt section (`heron_brook`) telling Opus 5 "Do not call the AgentTool unless the user requested it". Has it actually suppressed subagent use in my sessions?

Write and run a script over ~/.claude/projects/**/*.jsonl that finds assistant messages (including thinking blocks) where the model declined to use a subagent.

- Require BOTH an agent term (AgentTool / "Agent tool" / subagent) AND declining language ("won't spawn", "not calling", "forbids", "instruction against", "rather than spawning", "doesn't count as a user request", similar) in the same message. Either alone is far too noisy.<br>- Print the matching sentence, not the whole message. Group by session, not by message.<br>- Split into two buckets. HIGH CONFIDENCE: dated after my oldest install in ~/.local/share/claude/versions/* AND echoing the injected wording. OTHER: everything else, especially declines citing my own config (a numbered rule, CLAUDE.md, AGENTS.md, a fleet/worktree policy). Without this split my own instructions about subagents dominate the output and overstate the problem. Print OTHER in full so I can check it for contamination...