Fixing Gemini 3 Pro image 404 not found

Model requested: gemini-3-pro-image-preview
Region: us-central1 (or global)

GCP Project ID: project-bd6986e4-3e98-48aa-…
GCP Project Number:
Billing status: Enabled (active billing account)
Vertex AI API: Enabled
Auth method: Application Default Credentials (ADC)
SDK: google-genai (Python)

Use case:
Production image generation pipeline for cross-stitch / textile mockup
photography. Inputs are reference WinStitch PNG patterns. Outputs are
photorealistic mockup images used for marketing and pattern previews.
Expected volume: ~50–200 images/day during active runs.

Current error:
404 NOT_FOUND - “Publisher Model
projects/<PROJECT_ID>/locations/us-central1/publishers/google/models/
gemini-3-pro-image-preview was not found or your project does not have
access to it.”

Already tried:

  • Confirmed billing and Vertex AI API are enabled
  • Tried both us-central1 and global locations
  • gemini-2.5-flash-image works (confirms ADC/auth is correct)

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