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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

Two new content block types are handled instead of hitting the unknown-type path

You'll notice
Useful3 Signal5
Streaming Notable

Responses can now include mid-conversation model-switch and system blocks without hitting unknown-type handling.

What

Responses can now contain blocks of type fallback (the point where the API switched models) and mid_conv_system. Token accounting, block dispatch and the streaming handler all handle both explicitly, counting them as "other" tokens and returning quietly rather than treating them as unknown. An additional 400-error classifier also now recognises the effort_unsupported upstream error class.

Details
  • The existing output_config text match for that error class remains alongside the new classifier.
Evidence

case "mid_conv_system":

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 →