Claude Code spawned 821 agents on one markdown check

A Claude Code user asked for a markdown consistency check and got 821 spawned agents instead. Fifty million tokens burned in seconds, according to a Reddit thread on the token burn that had picked up 43 upvotes with a usage screenshot attached.

The stakes go past one bad bill. Running Claude Code on a task you'd call trivial gives you no built-in assurance the harness won't decide it needs hundreds of subagents to finish it. The thread doesn't say what set fan-out at 821, and it doesn't say if Anthropic responded.

That gap matters because it's the difference between a one-off bug and a pattern. Cost-optimization threads on r/ClaudeAI already trade tips for keeping subagent counts down. This post reads like the failure those tips exist to prevent. It happened in seconds, not over a long session.

Set a subagent budget before you run anything that touches many files, especially a task that smells like a full-repo sweep. A cap you set yourself beats discovering the harness had none.

Watch for whether Anthropic confirms a fan-out limit already existed and this was a bug. Until that shows up, treat unlimited subagent spawning as the default and budget for it.