Claude Code raises default subagent nesting depth to 3

Claude Code raised its default nested subagent spawn depth from 1 to 3 in v2.1.219, per the changelog. A subagent can now spawn a subagent that spawns a subagent, with no configuration required.

If you run agent fleets on a subscription or a fixed budget, that's a cost regression with no error message. It just shows up as "why did my usage spike." The depth change shipped within a day of Anthropic's Opus 5 prompting guide, which warns the model "delegates to subagents more readily than prior models" and that this "multiplies cost and time when applied to small tasks." Two changes, same week, compounding in the same direction, and nothing tied them together until now.

The fix is two changes, not a redesign. Set CLAUDE_CODE_MAX_SUBAGENT_SPAWN_DEPTH=1 to keep the old default, then paste Anthropic's delegation constraints into your system prompt: delegate only for large, independent work, never delegate to verify your own output, and prefer one subagent over several. I set both this morning. Depth 3 might be right for a research setup that wants an orchestrator spawning specialists, but I'd rather that be a decision I made, not a default I inherited.

The guide has a second fix worth more than the first: delete "verify your own work" instructions from your prompts. Opus 5 self-verifies, and lines like "include a final verification step" now cause over-verification, per Anthropic. Cutting them saves tokens without hurting quality. If you built writer-verifier scaffolding for Opus 4.x, you're paying twice for behavior the model already does for free.

There's a matching trap in code review prompts. Opus 5 follows scoping instructions literally, so telling it to "only report high-severity issues" makes it report fewer findings, real bugs included. Ask for everything, then filter severity afterward; accuracy holds even at lower effort settings, per Anthropic.

Teams that get burned by the new default will blame Opus 5's pricing before they check their subagent depth setting.