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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.

← All of v2.1.251 Home All releases ←olderv2.1.250

Claude Code v2.1.251 28 Aug 2026

MCP tool calls can no longer spawn subagents mid-call

You'll notice

Useful3 Signal3

MCP

An MCP tool call can no longer start a subagent Task while it runs.

What

MCP tool invocations dispatched over the SDK control channel now run with subagent spawning disabled, so a tool call cannot start a Task while it is running.

Details

Unconditional on this path.

Evidence

disallowTasks: !0

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

See this entry in the whole of v2.1.251 →