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MarkdownLLMs.txt

Gemini generateContent Format

This page covers nano-banana-2, nano-banana-pro, and nano-banana-2-lite. For Nano Banana 2.1, use the dedicated Gemini generateContent guide. Thinking control is not enabled for these older models or their fixed-resolution compatibility names.

In this page's examples, {BASE_URL} is https://api.uniall.ai.

Use this format with Gemini-style clients or when you need Base64 image input and output. The model is part of the URL, and image controls belong in generationConfig.imageConfig.

Endpoint​

POST /v1beta/models/{model}:generateContent

Replace {model} with nano-banana-2, nano-banana-pro, or nano-banana-2-lite.

Authentication​

x-api-key: sk-***
Content-Type: application/json

The same UniAll API key works for the OpenAI Images and Gemini formats.

Request Body Parameters​

ParameterTypeRequiredDescription
contentsarrayYesConversation content containing one user message.
contents[].rolestringYesUse user.
contents[].parts[].textstringYesGeneration or editing instruction.
contents[].parts[].inlineDataobjectConditionalReference image for editing. Repeat the part for multiple images.
inlineData.mimeTypestringConditionalImage media type, such as image/png.
inlineData.datastringConditionalRaw Base64 data without a Data URL prefix.
generationConfig.responseModalitiesstring[]YesUse ["TEXT", "IMAGE"] when text and image output are acceptable.
generationConfig.imageConfig.imageSizestringNo512, 1K, 2K, or 4K; defaults to 1K. Model limits apply.
generationConfig.imageConfig.aspectRatiostringNoOutput ratio such as 1:1, 3:4, or 16:9.
ModelSupported imageSize values
nano-banana-2512, 1K, 2K, 4K
nano-banana-pro1K, 2K, 4K
nano-banana-2-lite1K

Request Examples​

Text-To-Image Example​

curl -X POST "{BASE_URL}/v1beta/models/nano-banana-2:generateContent" \
  -H "x-api-key: sk-***" \
  -H "Content-Type: application/json" \
  -d '{
    "contents": [
      {
        "role": "user",
        "parts": [
          {
            "text": "A cinematic product photo of a clear perfume bottle on black stone, blue mist, no text"
          }
        ]
      }
    ],
    "generationConfig": {
      "responseModalities": ["TEXT", "IMAGE"],
      "imageConfig": {
        "imageSize": "512",
        "aspectRatio": "1:1"
      }
    }
  }'

Image Editing Example​

Encode the image as raw Base64 before building the JSON request:

IMAGE_BASE64="$(base64 < ./reference.png | tr -d '\n')"
{
  "contents": [
    {
      "role": "user",
      "parts": [
        {
          "text": "Keep the subject and composition; replace the background with a rainy neon street"
        },
        {
          "inlineData": {
            "mimeType": "image/png",
            "data": "BASE64_IMAGE_DATA"
          }
        }
      ]
    }
  ],
  "generationConfig": {
    "responseModalities": [
      "TEXT",
      "IMAGE"
    ],
    "imageConfig": {
      "imageSize": "2K",
      "aspectRatio": "3:4"
    }
  }
}

Add another inlineData part for each additional reference image. Keep the image order consistent with the prompt.

Response Examples​

{
  "candidates": [
    {
      "content": {
        "role": "model",
        "parts": [
          {
            "text": "Image generated."
          },
          {
            "inlineData": {
              "mimeType": "image/png",
              "data": "iVBORw0KGgoAAAANSUhEUgAA..."
            }
          }
        ]
      },
      "finishReason": "STOP"
    }
  ]
}

Find the part containing inlineData, Base64-decode its data, and save it using the returned mimeType. Some clients may normalize the field names to inline_data and mime_type.

Python Example​

import base64
import requests

response = requests.post(
    "https://api.uniall.ai/v1beta/models/nano-banana-2:generateContent",
    headers={"x-api-key": "sk-***", "Content-Type": "application/json"},
    json={
        "contents": [{
            "role": "user",
            "parts": [{"text": "An orange cat wearing an astronaut helmet"}],
        }],
        "generationConfig": {
            "responseModalities": ["TEXT", "IMAGE"],
            "imageConfig": {"imageSize": "512", "aspectRatio": "1:1"},
        },
    },
    timeout=600,
)
response.raise_for_status()

for candidate in response.json().get("candidates", []):
    for part in candidate.get("content", {}).get("parts", []):
        image = part.get("inlineData") or part.get("inline_data")
        if image and image.get("data"):
            with open("generated.png", "wb") as output:
                output.write(base64.b64decode(image["data"]))
            raise SystemExit(0)

raise RuntimeError("response did not contain an image")

Legacy Model IDs​

Earlier Gemini preview IDs that encode a fixed resolution may remain accepted for compatibility. They are deprecated and may be removed at any time. New integrations should use a unified Nano model in the URL and select imageSize in the request.

Billing Notes​

Billing depends on the model and imageSize. Check the current model price available to your account. The response may be large because it contains Base64 image data.

Common Errors​

  • Sending imageSize: "0.5k" or "512K"; use "512" for 0.5K.
  • Requesting 512 from nano-banana-pro or nano-banana-2-lite.
  • Including data:image/png;base64, in inlineData.data.
  • Looking only at the first response part instead of finding the part with inlineData.
  • Logging the full Base64 response or API key.