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609609You can cap that growth in three ways: how deeply subagents nest, how many run at once, and how much the whole query spends. Set the depth and concurrency limits as environment variables through the [`env`](/docs/en/agent-sdk/typescript#options) option, and the spend limit as a query option:
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611| Limit | Set it with | Default | What Claude Code does at the limit |
612| :---------- | :------------------------------------------------------- | :----------------------------------------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
613| Depth | [`CLAUDE_CODE_MAX_SUBAGENT_SPAWN_DEPTH`](/docs/en/env-vars) | `3` layers of subagents below your main agent. `1` stops your subagents from spawning any of their own | Leaves a subagent at the bottom layer unable to spawn, so it does its delegated work itself. See [nested subagents](/docs/en/sub-agents#let-subagents-spawn-their-own-subagents) |
614| 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 limit reached`, until the running count drops below the limit. Sessions with [ultracode](/docs/en/model-config#adjust-effort-level) active are never refused. See the [concurrent subagent limit](/docs/en/sub-agents#concurrent-subagent-limit) |
615| Spend | `maxBudgetUsd` in TypeScript, `max_budget_usd` in Python | No limit. Compared against `total_cost_usd`, so subagent requests count | Enforces the cap in three ways: refuses to spawn more subagents, returning `Budget limit reached`, stops background subagents that are still running, and ends the query with the `error_max_budget_usd` result subtype. See [turns and budget](/docs/en/agent-sdk/agent-loop#turns-and-budget) |
611| Limit | Set it with | Default | What Claude Code does at the limit |
612| :---------- | :------------------------------------------------------- | :----------------------------------------------------------------------------------------------------- | :----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
613| Depth | [`CLAUDE_CODE_MAX_SUBAGENT_SPAWN_DEPTH`](/docs/en/env-vars) | `3` layers of subagents below your main agent. `1` stops your subagents from spawning any of their own | Leaves a subagent at the bottom layer unable to spawn, so it does its delegated work itself. See [nested subagents](/docs/en/sub-agents#let-subagents-spawn-their-own-subagents) |
614| 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 limit reached`, until the running count drops below the limit. Sessions with [ultracode](/docs/en/model-config#adjust-effort-level) active are never refused. See the [concurrent subagent limit](/docs/en/sub-agents#concurrent-subagent-limit) |
615| Spend | `maxBudgetUsd` in TypeScript, `max_budget_usd` in Python | No limit. Compared against `total_cost_usd`, so subagent requests count | Enforces the cap in three ways: refuses to spawn more subagents, returning `Budget limit reached`, stops background subagents that are still running, and ends the query with the `error_max_budget_usd` result subtype. For how the caps behave across a session, see [turns and budget](/docs/en/agent-sdk/agent-loop#turns-and-budget) |
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617617The two SDKs treat the `env` option differently: the TypeScript SDK replaces the subprocess environment with it, so spread `process.env` into it to keep variables like `PATH`, while the Python SDK merges it into the inherited environment. This example turns nesting off, allows at most five subagents at a time, and stops the query once the estimated spend reaches \$5:
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