# Nano Banana family API: choosing a model, choosing an endpoint, and the response structure

Source: https://ofox.ai/docs/develop/models/nano-banana

Google's Gemini image models, five in total. We recommend calling them through the **Gemini native API**, which gives precise control over aspect ratio and resolution; the OpenAI-compatible API also works, but supports only some parameters.

## Common tasks

- [Set aspect ratio and resolution](https://ofox.ai/docs/develop/models/nano-banana/text-to-image) — Landscape, portrait and 4K images, and the values each model supports.
- [Editing & multi-image](https://ofox.ai/docs/develop/models/nano-banana/image-edit) — Upload images and edit them with a text instruction.
- [Troubleshooting errors](https://ofox.ai/docs/develop/models/nano-banana/errors) — 400 invalid argument, wrong aspect ratio, no image returned, 410.

## Choosing a model

**Key point**:Nano Banana 2 is recommended for most cases; choose Pro for 4K output or complex compositions, and 2 Lite for generating small images in bulk.

- **Nano Banana 2.1**(Latest): Three tiers: 1K, 2K, 4K; Aspect ratios from 1:8 to 8:1; 2K and 4K measured at about 2 minutes — gemini-nano-banana-2.1
- **Nano Banana 2**(Everyday pick): Four resolutions from 512 to 4K; Widest choice of aspect ratios, including 1:8 and 8:1 — gemini-3.1-flash-image
- **Nano Banana Pro**(Quality first): Three tiers: 1K, 2K, 4K; Reasons before generating, so it takes longer — gemini-3-pro-image
- **Nano Banana 2 Lite**(Speed first): 1K only; Measured at about 5 seconds per image; outputs JPEG — gemini-3.1-flash-lite-image
- **Nano Banana**(Previous gen): Fixed at about 1K; resolution cannot be set; Fine for existing projects — gemini-2.5-flash-image

**Model IDs (copy them exactly)**

- Nano Banana 2.1: `google/gemini-nano-banana-2.1` — Latest
- Nano Banana 2: `google/gemini-3.1-flash-image` — Everyday pick
- Nano Banana Pro: `google/gemini-3-pro-image` — 4K, complex compositions
- Nano Banana 2 Lite: `google/gemini-3.1-flash-lite-image` — 1K only
- Nano Banana: `google/gemini-2.5-flash-image` — Previous gen

For live prices, see the model pages: [Nano Banana 2](https://ofox.ai/models/google/gemini-3.1-flash-image), [Nano Banana Pro](https://ofox.ai/models/google/gemini-3-pro-image). The actual charge follows `usageMetadata` in the response.

## Choosing an endpoint

**Key point**:Use the Gemini native API when you need to control aspect ratio and resolution.

| | Gemini native API (recommended) | OpenAI-compatible API |
|---|---|---|
| Endpoint | `POST /gemini/v1beta/models/<model ID>:generateContent` | `POST /v1/images/generations`, `/v1/images/edits` |
| Aspect ratio | `imageConfig.aspectRatio` | Top-level `aspect_ratio` |
| Resolution | `imageConfig.imageSize`: 512, 1K, 2K, 4K | **Not supported**; sending `image_size` returns 400 |
| `size: "WIDTHxHEIGHT"` | Not applicable | Not supported; set the ratio with `aspect_ratio` |
| `n` (multiple images) | Not applicable | Not supported; one image per request |
| Editing | Put `inlineData` in `parts` | Upload files to `/v1/images/edits` |
| Reference images `input_images` | Not applicable | Not supported; use `/v1/images/edits` for editing |
| Returned in | `candidates[0].content.parts[].inlineData.data` | `data[0].b64_json` |

## Latency and timeouts

**Key point**:Set the client timeout to 300 seconds or more.

The API is synchronous. We measured about 5 to 20 seconds at 1K and about 30 seconds at 4K; Nano Banana 2.1 at 2K and 4K takes about 2 minutes. It takes longer at peak times. Pro reasons before generating the image (the response includes `thoughtsTokenCount`), so it is slower than Nano Banana 2 at the same resolution. The common 60-second default timeout does not cover 4K or peak-time requests; if the client disconnects, the request is still billed.

## Response structure

```json filename="200 OK (native API, data truncated)"
{
  "candidates": [{
    "content": {
      "parts": [{ "inlineData": { "mimeType": "image/png", "data": "iVBORw0KGgo…" } }],
      "role": "model"
    },
    "finishReason": "STOP"
  }],
  "modelVersion": "google/gemini-3-pro-image",
  "usageMetadata": {
    "promptTokenCount": 7,
    "candidatesTokenCount": 2000,
    "candidatesTokensDetails": [{ "modality": "IMAGE", "tokenCount": 2000 }],
    "thoughtsTokenCount": 211,
    "totalTokenCount": 2218
  }
}
```

- The image is in the `parts` item that contains `inlineData`, **not necessarily the first item**; text may come before it. Iterate over `parts` to find it.
- The `IMAGE` entry in `candidatesTokensDetails` gives the number of output image tokens. We measured 1,120 at 1K and 2,000 for Pro at 4K.
- `thoughtsTokenCount` appears only in Pro responses and counts the reasoning tokens used before generating the image.

## Official docs
The official docs describe behavior when calling Google directly; when calling through OfoxAI, the measured results on this page take precedence.

- [Gemini API · Image generation](https://ai.google.dev/gemini-api/docs/image-generation)
- [Gemini API · Aspect ratios and image size](https://ai.google.dev/gemini-api/docs/image-generation#aspect_ratios_and_image_size)
- [OfoxAI · Gemini native protocol generateContent](https://ofox.ai/docs/api/gemini/generate-content)

## FAQ

**How do I generate a 4K image with Nano Banana Pro?**

Use the Gemini native API and pass imageSize: "4K" in generationConfig.imageConfig, with aspectRatio to set the ratio. In our tests a 16:9 4K output was 5504x3072, about 16 MB, and took about 33 seconds. The OpenAI-compatible API does not support imageSize; sending image_size returns 400.

**Which aspect ratios does Nano Banana 2 support?**

Ten common ones: 1:1, 2:3, 3:2, 3:4, 4:3, 4:5, 5:4, 9:16, 16:9 and 21:9; plus four extra-wide or extra-tall ratios: 1:4, 4:1, 1:8 and 8:1. Any ratio not on the list returns 400 Request contains an invalid argument.

**Does Nano Banana Pro support 1:8 or 4:1?**

No. The four ratios 1:4, 4:1, 1:8 and 8:1 are supported only by Nano Banana 2.1, Nano Banana 2 and Nano Banana 2 Lite; use one of these three for extra-tall or extra-wide images.

**Should imageSize be 4K or 4k?**

We recommend uppercase 1K, 2K and 4K, matching Google. In our tests OfoxAI also accepts lowercase. The 512 tier has no K and is supported only by Nano Banana 2.

**How do I set the Nano Banana aspect ratio on the OpenAI-compatible API?**

Use the top-level aspect_ratio, e.g. "16:9". That API has no resolution parameter; for 2K or 4K use imageConfig.imageSize on the Gemini native API.

**Can Nano Banana generate several images at once?**

No, each request generates one image. For more, send several requests concurrently, keeping the rate limit in mind.

**What timeout should I set for Nano Banana?**

We recommend 300 seconds or more. We measured about 5 to 20 seconds at 1K, about 30 seconds at 4K, and about 2 minutes for Nano Banana 2.1 at 2K and 4K, longer at peak times. Pro reasons before generating, so it is slower than Nano Banana 2.