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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 v2.1.221 3 Aug 2026

Headless MCP pre-wait takes an options object and reports more telemetry

Under the hood

Useful1 Signal0

MCP

Waiting for MCP servers before a headless run is tidied up and logs more detail.

What

The helper that waits for MCP servers before a headless run swapped positional arguments for an options bag and emits richer telemetry.

Details

Options are skipTelemetry, waitForDeferrable, localOnly and permissionPromptToolServerName.
localOnly is now supplied by the caller instead of being inferred from CLAUDE_CODE_ENTRYPOINT.
Callers can request waiting even for servers that would otherwise be deferred.
The tengu_headless_mcp_prewait event gains deadlineMs and waitForDeferrable fields.

Evidence

tengu_headless_mcp_prewait

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

See this entry in the whole of v2.1.221 →