Org Account + Vertex Ai API KEY not working

[JuanKRuiz]

Hi,
I use my organization credentials to authenticate on Gemini CLi, it works perfectly.
Then according to documentation I configure .env file with this for enabling the extension.

GOOGLE_CLOUD_PROJECT_ID="gemini-vertex-ai-ABC123456"
NANOBANANA_GOOGLE_API_KEY="ABCDEFGHIJKLMNÑO"

But once I sent a command I get

 generate_diagram (nanobanana MCP Server) {"style":"technical","prompt":"chat application architecture","type":"a… │
│                                                                                                                      │
│    MCP error -32603: An unexpected error occurred: {"error":{"code":401,"message":"API keys are not supported by     │
│    this API. Expected OAuth2 access token or other authentication credentials that assert a principal. See           │
│    https://cloud.google.com/docs/authentication","status":"UNAUTHENTICATED","details":[{"@type":"type.googleapis.com │
│    /google.rpc.ErrorInfo","reason":"CREDENTIALS_MISSING","domain":"googleapis.com","metadata":{"method":"google.ai.g │
│    enerativelanguage.v1beta.GenerativeService.GenerateContent","service":"generativelanguage.googleapis.com"}}]}}

 An unexpected error occurred while trying to generate the diagram. The authentication failed because an API key was
  used, but this specific API requires an OAuth2 access token.

If I remove the NANOBANANA_GOOGLE_API_KEY then

generate_diagram (nanobanana MCP Server) {"prompt":"chat application architecture","style":"technical","type":"a… │
│                                                                                                                      │
│    MCP error -32603: ERROR: No valid API key found. Please set NANOBANANA_GEMINI_API_KEY, NANOBANANA_GOOGLE_API_KEY, │
│    GEMINI_API_KEY, or GOOGLE_API_KEY environment variable.                                                           │
│    For more details on authentication, visit:                                                                        │
│    https://github.com/google-gemini/gemini-cli/blob/main/docs/cli/authentication.md

✦ I am unable to generate the diagram. It seems there is an issue with the API key configuration. Please ensure that on
  of the following environment variables is set correctly: NANOBANANA_GEMINI_API_KEY, NANOBANANA_GOOGLE_API_KEY,
  GEMINI_API_KEY, or GOOGLE_API_KEY.

  For more detailed instructions on setting up authentication, you can visit the official documentation here:
  https://github.com/google-gemini/gemini-cli/blob/main/docs/cli/authentication.md

So it is a complete contradiction.

[gauravkakad-google]

+1 to this issue. We need support for ADC with VertexAI

[cnemri]

+1 to this issue

[equifaxboguo]

+1

[cpf-hse]

+1