Cap concurrent subagents at 3–5 unless the task truly fans out

Totalum·medium signal

The empirical sweet spot for parallel subagents is 3–5 concurrent; past that you spend more time merging summaries than you save, so only fan wider (tens to hundreds) for tasks that genuinely decompose into independent units. Before spawning, ask whether the work is truly parallel or just sequential work you're hoping to speed up. Default to a small pool with a strong synthesis step over a large pool with thin merges.