generateContent() fails with error: 'The "listener" argument must be of type function. Received an instance of Object'

[markabrahams]

When using @google/genai in Vertex AI mode with service account credentials (googleAuthOptions.credentials), the first API call fails during the OAuth token exchange (the request to get an access token from the token endpoint), e.g. the first call to generateContent().

Environment details

• Programming language: Node.js
• OS: Ubuntu 24.04
• Language runtime version: 24.13.0
• Package version: 1.44.0

Steps to reproduce

1. Create a new GoogleGenAI with googleAuthOptions.credentials and a GCP key object.
2. Call generateContent() with this.

e.g.

const ai = new GoogleGenAI({
  vertexai: true,
  project: '...',
  location: '...',
  googleAuthOptions: {
    credentials: { private_key, etc. ... }
  }
});
ai.models.generateContent({
  model: "gemini-2.5-flash",
  contents: "Hello"
});

Error:

The resulting error is of the form:

Error: The "listener" argument must be of type function. Received an instance of Object
    at Gaxios._request (.../node_modules/gaxios/src/gaxios.ts:227:15)
    at getToken (.../node_modules/google-auth-library/build/src/gtoken/getToken.js:52:26)
    at async TokenHandler.getToken (.../node_modules/google-auth-library/build/src/gtoken/tokenHandler.js:83:27)
    at async JWT.refreshTokenNoCache (.../node_modules/google-auth-library/build/src/auth/jwtclient.js:189:23)
    at async JWT.getRequestMetadataAsync (.../node_modules/google-auth-library/build/src/auth/oauth2client.js:372:17)
    at async JWT.getRequestHeaders (.../node_modules/google-auth-library/build/src/auth/oauth2client.js:336:26)
    at async NodeAuth.addGoogleAuthHeaders (.../node_modules/@google/genai/dist/node/index.cjs:18538:29)
    ...
    at async VertexAiClient.query (...)

Workaround:

Set fetch implementation to Node native:

const ai = new GoogleGenAI({
  vertexai: true,
  project: '...',
  location: '...',
  googleAuthOptions: {
    credentials: { ... },
    clientOptions: {
      transporterOptions: { fetchImplementation: globalThis.fetch }
    }
  }
});

[Varun-S10]

Hi @markabrahams, Thank you for bringing this to our attention. We truly appreciate you flagging this issue, we will file a bug internally.