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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 v2.1.228

Assistant messages carry two new null fields

Under the hood
Useful1 Signal1
API Client

Messages Claude Code writes itself now include two empty fields to match the upgraded message format.

What

Messages Claude Code synthesizes itself, such as tool-use notices, stop-sequence messages and virtual transcript entries, now set diagnostics: null and a null token-details field in usage, matching the upgraded SDK message type.

Evidence

diagnostics: null

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

Related

Other releases about the same thing. Found by shared names or similar wording; neither means one caused the other.

See this entry in the whole of v2.1.228 →