Add Google Gemini 3.1 verify models

[mayeco]

Add Gemini 3.1 model

Summary

Add Gemini 3.1 to verify models

Checklist

• If the PR is changing/adding functionality, are there tests to reflect this?
• If there is an example, have you run the example to make sure that it works?
• If there are instructions on how to run the code, have you followed the instructions and made sure that it works?
• If the feature is significant enough to require documentation, is there a PR open on the OpenHands/docs repository with the same branch name?
• Is the github CI passing?

[Copilot]

Pull request overview

Adds the Gemini 3.1 Pro preview identifier to the SDK’s “verified models” allowlist so it’s treated as a known/verified OpenHands-supported model.

Changes:

• Add "gemini-3.1-pro-preview" to VERIFIED_OPENHANDS_MODELS.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[mayeco]

@enyst please review.

[enyst]

Hey @mayeco thank you for the PR!

In "openhands verified" models we add models that

• we verified
• and, I think, they're available via openhands/ provider.

I'm not sure this is the case yet with 3.1. Maybe @neubig could advise on this?

[juanmichelini]

@mayeco thank you! As @enyst mentioned at the moment we are reviewing the model for quality with OpenHands.
We should have some results in the following days in the OpenHands index. Once we complete the benchmarking and the testing, we double check infra, if everything works we add it to the verified models list.

Notice that you can still use the model locally, just not with the SaaS at the moment.
I see you are using Gemini 3.1 would love to hear your feedback so far, and if there is anything we need to take into account while integrating it.

[mayeco]

hey @juanmichelini for now the Gemini 3.1 model is running very well, the only thing I have issues is the temperature reset in this

#2278 fixed in this PR: #2277