Tool search no longer disabled on Vertex AI

Tool search now runs on Vertex AI instead of being refused outright.

You'll notice Notable Improvements

JSON All of v2.1.221

You'll noticeTier: how much it should matter to you

4Useful: my rating, 1 to 5

0Signal: worth watching, 1 to 5

Tool UseArea: what it touches

ImprovementsKind: in v2.1.221, 03 Aug 26

What probably matters to youSection of the release

What

Optimistic tool search now runs on Vertex instead of being refused up front.

Details

The block that logged that Vertex "does not accept the tool-search beta header" and told you to set ENABLE_TOOL_SEARCH=true has been deleted.
The only remaining bail-out is for non-first-party ANTHROPIC_BASE_URL hosts.
ENABLE_TOOL_SEARCH still overrides the mode.

Evidence

ENABLE_TOOL_SEARCH

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

Read from

The build it came inv2.1.221

3 Aug 2026 · 308 entries, this one is #52.

Either side of it

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Names in this entry

envENABLE_TOOL_SEARCH
Tool search now runs on Vertex AI instead of being refused outright.
envANTHROPIC_BASE_URL
Override the API endpoint to route requests through a proxy or gateway. When set to a non-first-party host, MCP tool search is disabled by default. Set ENABLE_TOOL_SEARCH=true if your proxy forwards tool_reference blocks. As of v2.1.196, Remote Control is disabled when this points at a host other than api.anthropic.com, matching its behavior on Amazon Bedrock, Google Cloud's Agent Platform, and Microsoft Foundry

Is this right?

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