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DisclaimerUnofficial, and not affiliated with Anthropic. Nearly all of this is read straight out of what ships: npm bundles, captured prompts, published docs. Anthropic's own notes go in verbatim, marked as theirs. The rest is my reading, and every entry carries the strings behind it. If one looks wrong, vote it down and say why.

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Claude Code v2.1.217 21 Jul 2026

Concurrency Slot Tracking for Subagents

Subagents now properly claim and release a concurrency slot via takeConcurrencySlot() / onRunSettled(). The store now tracks runningSubagents as a counter. This enables accurate display of running agent count and proper enforcement of concurrent subagent limits (controlled by CLAUDE_CODE_MAX_CONCURRENT_SUBAGENTS).

Evidence

Concurrency tracking (search for "Concurrent subagent limit reached")

Strings lifted out of the shipped bundle, so the claim above can be checked against them.

See this entry in the whole of v2.1.217 →