Gemini-3-pro return Corrupted thought signature on multi step tool call

[Smilexuhc]

I am using the Vercel AI SDK with the OpenRouter provider to access Google Gemini-3-pro-preview model.

During a conversation, specifically when context history is involved (multi-step tool call), the API returns error with the message "Corrupted thought signature."

version: @openrouter/ai-sdk-provider 1.3.0
provider: google ai studio

[mattapperson]

Could you provide an example of this happening to help us reproduce and resolve the issue?

[SteffenDE]

I think the issue is that the reasoning_details in the providerMetadata gets replaced instead of merged, which can be seen in this demo repo:

https://github.com/SteffenDE/openrouter-ai-sdk-issue

If you run this and send a message, you can see that the reasoning chunk gets updated, but the details array is always overwritten. In the screenshot you can see that the reasoning text starts with "**Evaluating..." (the first chunk, later ones are appended to the text), but the details only contain the last chunk (starting with "**Composing...").