Ability to pass vertexai: true in @langchain/google-genai

[mbruhler]

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Example Code

const ai = new GoogleGenAI({
    vertexai: true,
    project: GOOGLE_CLOUD_PROJECT,
    location: GOOGLE_CLOUD_LOCATION,
});

Hi,
I want to use @langchain/google-genai but in a way as Google show in their docs https://cloud.google.com/vertex-ai/generative-ai/docs/sdks/overview#googlegenaisdk_quickstart-nodejs_genai_sdk

But can't find a way to initialize ChatGoogleGenerativeAI (https://v03.api.js.langchain.com/classes/_langchain_google_genai.ChatGoogleGenerativeAI.html) in @langchain/google-genai

Is there a possibility to use this client but using VertexAI platform?

### System Info

        "@langchain/core": "0.3.43",
        "@langchain/google-vertexai": "0.2.3",
        "@langchain/openai": "0.5.0",
        "langchain": "0.3.19",
        
        Node 20.10.0

[dosubot[bot]]

Hi @mbruhler! I'm Dosu and I’m helping the langchainjs team.

The @langchain/google-genai package does not support a vertexai option and cannot be used to connect to Vertex AI endpoints. It is designed to work directly with Gemini models via the Google Generative AI SDK and requires an API key, not Vertex AI credentials. If you want to use Vertex AI (for example, to specify project and location), you should use the @langchain/google-vertexai package instead. This package is built specifically for Vertex AI endpoints and supports the configuration you’re looking for. You can find setup and usage details in the LangChain docs and see examples of initializing ChatVertexAI with your project and location settings.

There is no way to pass vertexai: true or similar to @langchain/google-genai or ChatGoogleGenerativeAI—this is a deliberate separation in the LangChain ecosystem to avoid confusion between the two platforms and their authentication methods. For Vertex AI, stick with @langchain/google-vertexai for best results.
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