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Gemini Image Generation

POST /v1beta/models/{model}:generateContent
As of April 14, 2026, the latest production retest against Crazyrouter showed:
  • gemini-3.1-flash-image-preview returned inlineData when called with responseModalities: ["IMAGE"]
  • gemini-3-pro-image-preview returned text containing a Markdown image with a data:image/...;base64,... payload
  • gemini-2.5-flash-image also returned text containing data:image/...;base64,...
  • gemini-2.5-flash-image-preview returned text containing a hosted image URL
Gemini image models do not currently share one uniform response shape on Crazyrouter. Do not assume every model will return inlineData.
If you are migrating from the Nano Banana family, do not keep using /v1/images/generations. nano-banana-2 should now move directly to gemini-3.1-flash-image-preview:generateContent. nano-banana can return image output through gemini-2.5-flash-image:generateContent, but billing consistency is still under review.

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Most Practical Current Example

For the specific goal of getting image bytes directly, the easiest current model to handle is gemini-3.1-flash-image-preview: 
curl "https://crazyrouter.com/v1beta/models/gemini-3.1-flash-image-preview:generateContent?key=YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "contents": [
      {
        "role": "user",
        "parts": [
          {"text": "Generate an IMAGE of a simple red square on a white background. Return image output."}
        ]
      }
    ],
    "generationConfig": {
      "responseModalities": ["IMAGE"]
    }
  }'
Observed production response shape: 
{
  "candidates": [
    {
      "content": {
        "parts": [
          {
            "inlineData": {
              "mimeType": "image/png",
              "data": "iVBORw0KGgoAAA..."
            }
          }
        ]
      }
    }
  ]
}

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Other Observed Output Shapes

The same-day production check also showed these model-specific differences:
  • gemini-3-pro-image-preview: parts[0].text looked like ![image](data:image/jpeg;base64,...)
  • gemini-2.5-flash-image: parts[0].text looked like ![image](data:image/png;base64,...)
  • gemini-2.5-flash-image-preview: parts[0].text looked like ![Image](https://...)
If you need to support multiple Gemini image models, parse in this order:
  1. Check inlineData first
  2. Then check whether text contains data:image/
  3. Then check whether text contains a hosted image URL
This page no longer keeps aspect-ratio or multi-image parameter guidance, because those parameters were not revalidated in this production pass.