Gemini 3.1 Flash Image（Nano Banana 2）

POST/v1beta/models/gemini-3.1-flash-image:generateContent

Generate or edit images with Nano Banana 2 through the native Google Gemini protocol. SandBase preserves the provider request and response payload instead of converting it to Chat Completions.

Request body

Send a native Gemini GenerateContent body. Provider-defined fields are passed through for this model.

arraycontentsrequired

Gemini Content objects containing the prompt and optional input images.

array<string>generationConfig.responseModalitiesrequired

Requested output modalities. Include IMAGE; include TEXT when you also want a text part.

Optional<object>generationConfig.imageConfig

Image options such as aspectRatio, when supported by the provider.

curl -X POST \
  "https://api.sandbase.ai/v1beta/models/gemini-3.1-flash-image:generateContent" \
  -H "x-goog-api-key: $SANDBASE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "contents": [{
      "role": "user",
      "parts": [{"text": "Create a wide editorial illustration of a solar-powered city at sunrise."}]
    }],
    "generationConfig": {
      "responseModalities": ["IMAGE"],
      "imageConfig": {"aspectRatio": "16:9"}
    }
  }'

Response200 OK

{
  "candidates": [
    {
      "content": {
        "role": "model",
        "parts": [
          {
            "inline_data": {
              "mime_type": "image/png",
              "data": "<base64-image>"
            }
          }
        ]
      },
      "finishReason": "STOP",
      "index": 0
    }
  ],
  "usageMetadata": {
    "totalTokenCount": 980
  }
}

Edit an image

Add the source image as an inlineData part next to the text instruction. Use the MIME type of the bytes you send:

{
  "contents": [{
    "role": "user",
    "parts": [
      {"text": "Keep the subject unchanged and turn the background into a paper-cut landscape."},
      {"inlineData": {"mimeType": "image/png", "data": "<base64-input-image>"}}
    ]
  }],
  "generationConfig": {"responseModalities": ["IMAGE"]}
}

Response handling

Read generated media from the returned candidate parts. Because this model uses native passthrough, provider-defined field casing and MIME metadata are returned as received. Decode the base64 payload and verify the actual media bytes before choosing a file extension.

Official Google resources

• Gemini API documentation
• Image generation documentation
• GenerateContent API reference