Imagen 3 and Imagen 4 publisher models return 404 in a new Vertex AI project while Gemini image generation works

Google Cloud Build with AI Generative AI & Foundational Models
1

Hello,

I am unable to access any Imagen publisher model in a newly created Google Cloud / Vertex AI project.

Environment:

  • Region: us-central1
  • Vertex AI API: enabled
  • Billing account: active
  • Model access organization policy (vertexai.allowedModels): not enforced
  • Vertex AI service agent: created and granted roles/aiplatform.serviceAgent
  • OAuth authentication using a service account: successful
  • Vertex AI TTS request: successful
  • Gemini image generation (Nano Banana Pro) in the Google Cloud console: successful

However, all of the following Imagen models return the same 404 error when tested directly in Vertex AI Studio, without using n8n or any external workflow:

  • imagen-4.0-fast-generate-001
  • imagen-4.0-generate-001
  • imagen-4.0-ultra-generate-001
  • imagen-3.0-capability-001

Example endpoint:

https://us-central1-aiplatform.googleapis.com/v1/projects/[REDACTED-PROJECT-ID]/locations/us-central1/publishers/google/models/imagen-4.0-fast-generate-001:predict

Error:

Publisher model ... was not found or your project does not have access to it. Ensure you are using a valid model name and that the model is available in the specified region. Status: NOT_FOUND (404).

Additional verification:

The exact same preflight workflow, model name, API version (v1), region (us-central1), and :predict request succeeded in my previous Google Cloud project on July 27, 2026. In the new project, credential validation, OAuth token creation, and Vertex AI TTS all succeed, but the Imagen request alone returns 404.

I also recreated the Vertex AI service identity and verified its service-agent role, but the issue remains.

Could a Googler please confirm whether this new project is missing Imagen publisher-model access or requires an additional backend entitlement/allowlist activation? I can provide the full project ID and diagnostic report privately if required.

Thank you.

2

Update ā€” August 3, 2026

I tested Imagen 4 Fast again today in the Google Cloud console, but the same 404 error still occurs:

Publisher model imagen-4.0-fast-generate-001 was not found or your project does not have access to it.

I also rechecked the project configuration using Cloud Shell:

  • Project lifecycle state: ACTIVE

  • Vertex AI API (aiplatform.googleapis.com): ENABLED

  • My user account has the Owner role

  • Vertex AI service agent exists

  • Service agent role: roles/aiplatform.serviceAgent

  • Effective vertexai.allowedModels organization policy: allowAll: true

  • Billing and free-trial credits: active

  • Region: us-central1

Vertex AI TTS and OAuth authentication work correctly. Only the Imagen publisher models continue to return 404, including when tested directly in the Google Cloud console without n8n or any external workflow.

This appears to be a backend entitlement or publisher-model access issue specific to the new project. Could a Google representative please check whether Imagen publisher-model access is enabled for this project?

I can provide the project ID, project number, and diagnostic screenshots privately if required.