The fix is incomplete as we expect google under providerMetadata, right now it is vertex.

From a user perspective:

Step 1: Tool Call Generation (Output)

(i) What I put in: A generateText call using @ai-sdk/google-vertex with a Gemini 3 thinking model.

(ii) What I get back: The reasoning state is returned under providerMetadata: { vertex: { thoughtSignature: "..." } }.

(iii) Expected behavior: Per Google Cloud Documentation, the thoughtSignature is a native field of the Gemini Part object. It should be returned under the google namespace to maintain consistency with the Google AI provider and allow for universal history persistence.

Step 2: Tool Result Resumption (Input)

(i) What I put in: I pass the history back to the Vertex provider. Following the standard convention, the signature is provided under the google namespace.

(ii) What I get back: A 500 Internal Server Error from Vertex AI.

(iii) Expected behavior: The model should resume reasoning.

i verified the fix for the reproduction code snippet you provided and the pr fixed the error! so assuming the bug only produces in a setup like your repro, the fix should be enough.

we specifically allow keeping vertex as provider option key name since there were previous requests of doing so for keeping a track when using vertex provider.

under the hood, you can rest assure that the needed providerOptions are passed how the endpoint expects them

If user set providerOptions with key google, let's say thinkingConfig, right now what I got is vertex in providerMetadata.

I would expect google in providerMetadata as stated in Vertex AI and for consistency reason.

I noticed that providerOptionsName is selected by hardcoded provider Name for @ai-sdk/google-vertex instead of provider key in providerOptions in this logic.

@buibaoanh the mapping isn't 1-1 if you compare it to google's sdk but that is by design of the AI SDK

there is a reason for why it's mapped to vertex instead of google and you can see here and here why

the ideal dx for setting providerOptions when using vertex provider is that the user defines the key to be vertex

@aayush-kapoor Ok, what about google-vertex docs refer to google as namespace for both providerOptions and providerMetadata?

@buibaoanh thanks for pointing out, will update the docs