How do we go about specifying the aspect ratio of the generated image?

[JamesDerrickHH]

Hi, I've managed to get image generation working well on an Azure Function, using this library, but currently always get a square, 1024x1024, image returned. Is there any way to change this?

Looking in the API Reference documentation there is an ImageConfig object, which allows aspectRatio, however, I get typescript errors when I try to use this

e.g.

        const model = vertexAI.getGenerativeModel({
            model: 'gemini-2.5-flash-image',
            generationConfig: {
                imageConfig: {
                    aspectRatio: "16:9",
                    imageSize: "1K"
                }
            }
        })

But I get the following typescript error
Object literal may only specify known properties, and 'imageConfig' does not exist in type 'GenerationConfig'.

Any help would be greatly appreciated