What
When you use Claude on Google Vertex, Claude Code checks whether your account can reach the models it wants to use. This check is called a probe.
- The old probe function, which cached results and logged lines like
[vertex-probe] ...: accessible (cached), has been removed. - New functions probe whether the default and fallback models are accessible. They remember the results, record models that were refused, and log
[3p-model-memory] vertex record failedwhen saving a result fails. - Results are keyed on
ANTHROPIC_VERTEX_PROJECT_ID,ANTHROPIC_GOOGLE_CLOUD_PROJECT,ANTHROPIC_VERTEX_BASE_URL,GOOGLE_APPLICATION_CREDENTIALS,CLOUDSDK_CONFIGandCLAUDE_CODE_SKIP_VERTEX_AUTH, so changing any of them triggers a fresh check.
Why
On Vertex, Claude Code now remembers which models your account cannot use and checks the fallback model too. This can lead to an automatic switch to another model when one is not available. Changing your project, endpoint or credentials starts the check over.
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It is not clear what starts the test, whether it is switched on for everyone, or whether it leads to Claude Code switching models on its…