What
Subagent spawning previously refused once a subagent hit both a fixed lifetime total and a fixed concurrent-run cap. Now only the concurrent-run limit remains, defaulting to 20 and overridable with the CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS environment variable. When the cap is reached, a new subagent launch is refused with a message telling the user to raise CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS, and the refusal is recorded as a subagent_concurrency_cap event.
Why Dropping the separate lifetime-total cap means subagents are no longer blocked just because many have run in sequence over a long session; only how many are running at once matters now, and that limit can be tuned per environment.
tengu_amber_kestrel Not enough to sayNothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.
This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.275: off
These values were read against a different version of Claude Code, so treat them as the nearest reading available instead of one taken on this release.
Read once, for one account on one subscription tier, against v2.1.275. It isn't a statement about your account. What a flag value here can and cannot tell you
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
If your harness is Claude Code or the Claude Agent SDK, the deterministic caps are the `CLAUDE_CODE_MAX_SUBAGENT_SPAWN_DEPTH` and `CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS` environment variables and the SDK's `max_budget_usd` (python; typescri…build-with-claude/prompt-engineering/prompting-claude-opus-5 see the edit
| Concurrency | [`CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS`](/docs/en/env-vars) | `20` subagents running at once, counting every subagent Claude spawns with the Agent tool | Refuses to spawn another subagent, returning `Concurrent subagent lim…agent-sdk/subagents see the edit
Anthropic's documentation has since written up CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS, on Subagents in the SDK.