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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 v2.1.234 17 Aug 2026

MCP idle timeouts are classified as unreachable, not generic failures

Under the hood

Useful2 Signal2

MCP

MCP servers that go silent are now reported as unreachable rather than a generic error.

What

When an MCP server sends neither a response nor progress before the idle timeout, the resulting error now carries mcpErrorSource: "downstream_unreachable", joining the existing "downstream_error" and "user_auth" sources. Both MCP client code paths are covered.

Evidence

mcpErrorSource: "downstream_unreachable"

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

See this entry in the whole of v2.1.234 →