Add support for image_size parameter for google/gemini-3-pro-image-preview

[ruxandraboghean]

I am using the OpenRouter API to generate images via:

model: "google/gemini-3-pro-image-preview"
endpoint: /chat/completions
modalities: ["image", "text"]

Currently, the model supports:

{
  "image_config": {
    "aspect_ratio": "16:9"
  }
}

But it does not support:

{
  "image_config": {
    "image_size": "4k"
  }
}

The API should include a parameter that allows requesting specific resolutions (1k, 2k, 4k).

[gurucodersro]

Same issue here, whatever I send as image_size it's always generating 1024x1024 px, it does not work. Nano Banana Pro added support for image_size, the previous version of Nano Banana did not have it.

[jonalange]

Any update on this? For me it sometimes generates 22mb large images with 4K but sometimes not and then fallsback to normal 1024px