Source Intelligence

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 v2.1.221 Home All releases olderv2.1.220 v2.1.222newer

Tool search refused for pre-4.5 models on Vertex

You'll notice
Useful4 Signal0
MCP

Fixes older Vertex models erroring on tool search; they now just load MCP tools normally.

What

Vertex-served older models rejected the tool-search beta header; those sessions now fall back to loading MCP tools normally instead of deferring them behind ToolSearch.

Details
  • applies only when the provider is vertex, and matches claude-3* models plus opus/sonnet/haiku models outside generations 4 and 5
  • short-circuits the tool-search capability check with reason vertex_model_unsupported
  • the same check is applied at the MCP-deferral, tool-search-tool-injection and headless MCP prewait call sites
  • the periodic tool-search reminder is suppressed for those models
Evidence

Tool search disabled for model '${e}' on Vertex: this model's Vertex serving stack rejects the tool-search beta header (pre-4.5 generation)., this model's Vertex serving stack rejects the tool-search beta header (pre-4.5 generation).

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

See this entry in the whole of v2.1.221 →