What probably matters to youSection of the release
What
The optimistic tool-search path now logs a single debug line naming its mode and the ENABLE_TOOL_SEARCH value, and refuses outright when ANTHROPIC_BASE_URL points at something other than a first-party Anthropic host.
Details
The refusal message tells you to set ENABLE_TOOL_SEARCH=true (or auto, or auto:N) if your proxy forwards tool_reference blocks.
The explanation is emitted once, not per request.
Evidence
is not a first-party Anthropic host. Set ENABLE_TOOL_SEARCH=true (or auto / auto:N) if your proxy forwards tool_reference blocks.
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed sinceAnthropic's documentation has since written up ANTHROPIC_BASE_URL, on Claude Code changelog.* Fixed every turn failing with HTTP 400 on third-party Anthropic-compatible endpoints (`ANTHROPIC_BASE_URL`) since 2.1.265: a regex in the Artifact tool's input schema that those endpoints rejectchangelogsee the edit
How sure we are
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agreesAnthropic's documentation has since written up ANTHROPIC_BASE_URL, on Claude Code changelog.
