The instinct makes sense. You're running three or four parallel Claude Code agents and the throughput is noticeably higher than sequential work. So you push further — to eight, to twelve, to twenty. If a few agents are good, more must be better.
What people find instead is that the gains flatten and then reverse. Not just "more overhead" — the failure mode at 20 agents is qualitatively different from the failure mode at 5. New things break that didn't break before, and they break in ways that aren't immediately obvious.
This is a breakdown of what those failure modes actually are, because naming them clearly is the prerequisite for avoiding them.
the failure modes that appear at scale
1. API throughput becomes the bottleneck
