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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

Startup records why fast start was disabled

Under the hood

Useful2 Signal2

Elsewhere

Startup now records why fast start was turned off rather than just that it was.

What

The startup state now carries a reason for why fast-start mode was turned off, plus a provisional startup mode, rather than only a bare flag saying it happened.

Evidence

fastModeBreakerReason

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 →