Cannot use gemini-3-pro-preview with Vertex AI Reasoning Engine in us-central1 (404 NOT_FOUND)

[enesdemirag]

I’m trying to migrate from Gemini 2.5 to Gemini 3 using Vertex AI Reasoning Engine + ADK (sessions + memory). My project and agent engine are in us-central1. When I set an agent model to gemini-3-pro-preview, I get:

google.genai.errors.ClientError: 404 NOT_FOUND. {'error': {'code': 404, 'message': 'Publisher Model `projects/<project>/locations/us-central1/publishers/google/models/gemini-3-pro-preview` was not found or your project does not have access to it. Please ensure you are using a valid model version.'}}

I tried:

• Using gemini-3-pro → same 404
• Using global location → 400 INVALID_ARGUMENT (Reasoning Engine endpoint requires locations like us-central1)
• Looking for allowlist access in Model Garden → no request access button visible

Because the Reasoning Engine endpoint is locked to us-central1, I can’t switch to the global region that supports gemini-3-pro-preview. I cannot see any "global" option on the regions list on the Google Cloud Console Vertex AI pages. I need guidance on how to enable Gemini 3 for Reasoning Engine in us-central1, or how to request allowlist access, or how to create it in global region. (Without codebase changes on Google ADK side.)

References

• Model versions: https://docs.cloud.google.com/vertex-ai/generative-ai/docs/learn/model-versions
• Migration guide: https://docs.cloud.google.com/vertex-ai/generative-ai/docs/migrate

[VariableVic]

This workaround fixed it for me: #3628 (comment)

[enesdemirag]

Thank you so much its working.