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Gemini Image Generation

POST /v1beta/models/{model}:generateContent
As of March 23, 2026, production checks 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.

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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.