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Certain Chat Completion models possess native image generation capabilities. This page explains how to use this feature with those specific models.
For dedicated image generation models like Flux, Imagen & others, please refer to the Images Generations API Reference.

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How to Generate Images

To generate an image, send a standard Chat Completion request to a compatible model with a clear text prompt asking for an image. 
{
  "model": "gemini-3-pro-image-preview",
  "messages": [
    {
      "role": "user",
      "content": "Generate a beautiful sunset over mountains"
    }
  ]
}

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Streaming

Image generation also works with streaming. Set "stream": true in your request to receive the response as a stream of events. 
{
  "model": "gemini-3-pro-image-preview",
  "messages": [
    {
      "role": "user",
      "content": "Create an image of a futuristic city"
    }
  ],
  "stream": true
}

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Configuration Options

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Aspect Ratio & Resolution

For the gemini-3-pro-image-preview model, you can control the aspect ratio and resolution (image size) of generated images using the image_config parameter: 
{
  "model": "gemini-3-pro-image-preview",
  "messages": [
    {
      "role": "user",
      "content": "Generate a beautiful sunset over mountains"
    }
  ],
  "image_config": {
    "aspect_ratio": "16:9",
    "image_size": "4K"
  }
}
Supported aspect ratios:
  • 1:1 - Square
  • 2:3 - Portrait
  • 3:2 - Landscape
  • 3:4 - Portrait
  • 4:3 - Landscape
  • 4:5 - Portrait
  • 5:4 - Landscape
  • 9:16 - Vertical (mobile)
  • 16:9 - Widescreen
  • 21:9 - Ultra-wide
Supported image sizes (resolution):
  • 1K
  • 2K
  • 4K

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Response Format

The generated image will be included in the assistant’s message in an images array. 
{
  "choices": [
    {
      "message": {
        "role": "assistant",
        "content": "I've generated a beautiful sunset image for you.",
        "images": [
          {
            "type": "image_url",
            "image_url": {
              "url": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAA..."
            }
          }
        ]
      }
    }
  ]
}

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Discover Supported Models

You can see which Chat Completion models support native image generation on the NagaAI Models page.