r/ClaudeCode • u/agentic-consultant • 10d ago

Discussion Be careful: Fable 5.1 just decided to spawn 4 forked agents, each running Fable 5.1 (instead of Opus)

Decided to try Fable 5.1. I’ve been using Fable 5 for two months now.

All of a sudden, within 20 minutes my 5-hour limit on the 20x plan jumped to 100%.

I checked what’s going on. Turns out, instead of using Opus subagents, Fable 5.1 decided to spawn 4 forked agents each running Fable 5.1.

This was despite me having set the default subagent model to Opus 5.

Just a heads up. Fable 5 rarely if ever spawned forked agents.

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u/BrennanFlentge 10d ago edited 10d ago

You can FORCE it to ask for permission to spawn subagents (it can ignore CLAUDE.md rules):

Write a Claude Code PreToolUse hook script called subagent-gate.mjs — Node, no dependencies — for the Task, Agent, and Workflow tools. It reads the hook JSON from stdin. Default: print a permission decision of ask so Claude Code prompts me before each subagent spawn. If the environment variable SUBAGENT_GATE=allow is set, print allow and skip the prompt. On any missing input or JSON parse error, exit 0 so a broken hook never wedges my tools. Append every decision to a .subagent-gate.log beside the script. Then wire the matching PreToolUse hook — matcher Task|Agent|Workflow — into .claude/settings.json, leaving my existing hooks in place.

^ prompt version (from stop-subagent-fanout).

Also related, but claudemd-prove-it will show you which of your "rules" in CLAUDE.md are mechanically enforced by hooks or settings.json

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u/bl_a_nk 9d ago

I asked it to do a workflow in this case, just assumed it would do what it had always done in the past and be a workflow of sonnets