Before Claude Code 2.1.216, hitting --max-budget-usd denied new subagent spawns but let already-running background subagents keep burning past the cap. 2.1.216 halts them at the ceiling and adds CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS (default 20) to bound how many contexts draw tokens in parallel. Upgrade and set both to give a long fan-out a true spend ceiling plus a parallelism throttle.
Give Your Agent Fleet a Real Dollar Ceiling: --max-budget-usd Now Halts Background Subagents
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