# FLUX.2 [klein] 4B

> Compact 4-billion parameter text-to-image model from Black Forest Labs. Step-distilled to 4 inference steps for sub-second generation. Unifies text-to-image and image editing in a single architecture with Apache 2.0 licensing.

## Overview

- **Endpoint**: `https://api.runflow.io/v1/run/black-forest-labs/flux-2-klein-4b`
- **Model ID**: `black-forest-labs/flux-2-klein-4b`
- **Provider**: Black Forest Labs
- **License**: commercial
- **Last Updated**: 2026-04-06

## Pricing

- **Base price**: $0.014/megapixel
- **Note**: Default price per megapixel
## Input Schema

### `prompt` (string, required)

Text description of the image to generate.

### `image_size` (string, optional)

Size preset for the generated image. Alternatively use width/height for custom dimensions.
- **Default**: `landscape_4_3`
- **Options**: `square_hd`, `square`, `portrait_4_3`, `portrait_16_9`, `landscape_4_3`, `landscape_16_9`

### `num_images` (integer, optional)

Number of images to generate (1-4).
- **Default**: `1`
- **Min**: 1
- **Max**: 4

### `num_inference_steps` (integer, optional)

Number of denoising steps. Default 4 for distilled variant, use higher for base variant.
- **Default**: `4`
- **Min**: 1
- **Max**: 50

### `guidance_scale` (number, optional)

Classifier-free guidance scale. Higher values follow the prompt more closely.
- **Default**: `2.5`
- **Min**: 0
- **Max**: 20

### `seed` (integer, optional)

Random seed for reproducible generation. Leave empty for random.

### `output_format` (string, optional)

Output image format.
- **Default**: `png`
- **Options**: `jpeg`, `png`, `webp`

### `enable_safety_checker` (boolean, optional)

Enable NSFW content filtering.
- **Default**: `true`

### `sync_mode` (boolean, optional)

Wait for the result synchronously instead of returning a request ID.
- **Default**: `false`

## Usage Examples

### cURL

```bash
curl -X POST https://api.runflow.io/v1/run/black-forest-labs/flux-2-klein-4b \
  -H "Authorization: Bearer $RUNFLOW_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "prompt": "A professional headshot, soft studio lighting",
    "output_format": "png"
  }'
```

### Python

```python
import requests

response = requests.post(
    "https://api.runflow.io/v1/run/black-forest-labs/flux-2-klein-4b",
    headers={"Authorization": "Bearer RUNFLOW_API_KEY"},
    json={
        "prompt": "A professional headshot, soft studio lighting",
        "output_format": "png",
    },
)

data = response.json()
print(data["images"][0]["url"])
```

### JavaScript

```javascript
const response = await fetch(
  "https://api.runflow.io/v1/run/black-forest-labs/flux-2-klein-4b",
  {
    method: "POST",
    headers: {
      "Authorization": "Bearer RUNFLOW_API_KEY",
      "Content-Type": "application/json",
    },
    body: JSON.stringify({
      prompt: "A professional headshot, soft studio lighting",
      output_format: "png",
    }),
  }
);

const data = await response.json();
console.log(data.images[0].url);
```

## Additional Resources

- [Playground](https://www.runflow.io/models/black-forest-labs/flux-2-klein-4b)
- [API Reference](https://www.runflow.io/models/black-forest-labs/flux-2-klein-4b/api)
- [Documentation](https://www.runflow.io/docs)