Hyperparameters for GenAI

[daveSignil]

Hello! I hope someone can shed some light on an issue i'm having.

I am having an issue with consistency when switching from Vertex API to GenAI API.

Having identical model and hyperparamters, for the same prompt generated via:
Vertex API: I get consistent results all the time.
In GenAI API: Wildly varying results.

Extracted relevant code:

For VertexAI I have:

vertexAi = new VertexAI({

project: this.PROJECT,

location: "europe-west1",

});

const model = this.vertexAi.getGenerativeModel({

model: "gemini-2.0-flash-001",

systemInstruction: systemInstruction,

generationConfig: {

    temperature: 0.0,

    topP: 0.1,

    topK: 10,

    seed: 1337,

    responseMimeType: "application/json",

    responseSchema: schema,

},

});

aiResponse = await model.generateContent({

    contents: [

        {role: "user", parts: [{text: JSON.stringify(lastUserMessage)}]},

    ],

});

____

For GenAI API I have:

genAI = new GoogleGenerativeAI(config.apiKey);

const model = this.genAI.getGenerativeModel({

    model: "gemini-2.0-flash-001",

    systemInstruction: systemInstruction

});

const aiResponse = await model.generateContent({

contents: [

{role: "user", parts: [{text: JSON.stringify(lastUserMessage)}]},

],

generationConfig: {

    temperature: 0.0,

    topP: 0.1,

    topK: 10,

    seed: 1337,

    responseMimeType: "application/json",

    responseSchema: schema,

},

});

Basically just the generation config moved as per the documentation.

Anyone have any insights? I'm pretty sure temperature etc is not being taken into account in my GenAI version.