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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 v2.1.219

Two new API betas documented: scalar fallbacks: "default" and mid-conversation tool changes

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Skills Notable not in their notes

Docs now describe two beta headers for automatic refusal fallbacks and swapping tools mid-conversation.

server-side-fallback-2026-07-01mid-conversation-tool-changes-2026-07-01defer_loading
What

The skill documents two beta headers that did not appear in the previous build's docs.

Details
  • fallbacks: "default" sits behind server-side-fallback-2026-07-01 and lets the server pick the fallback by refusal category; the array form stays on server-side-fallback-2026-06-01, and pairing either header with the other form returns 400.
  • A new tool-use-concepts section covers mid-conversation-tool-changes-2026-07-01: tool_addition and tool_removal blocks on a role: "system" message change the tool set between turns without invalidating the prompt cache.
  • Tools involved must be declared with "defer_loading": True.
Evidence

mid-conversation-tool-changes-2026-07-01

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

See this entry in the whole of v2.1.219 →