# FLUX.2 [klein] 4B

FLUX.2 [klein] 4B is the only FLUX.2 model released under Apache 2.0, a fully open license that permits unrestricted commercial use and redistribution. It targets inference under half a second.

- **Model ID:** `bfl/flux-2-klein-4b`
- **Type:** image
- **Providers:** bfl
- **Context window:** Not applicable
- **Maximum output tokens:** 0
- **Pricing:** See the provider details below
- **Canonical page:** https://vercel.com/ai-gateway/models/flux-2-klein-4b

## Supported parameters

- **Parameters:** `seed`
- **Operations:** `text-to-image`, `image-to-image`
- **Input modalities:** `text`, `image`
- **Output modalities:** `image`
- **Aspect ratios:** Not reported
- **Resolutions:** Not reported
- **Durations:** Not reported
- **Frame rates:** Not reported
- **Maximum outputs per request:** Not reported
- **Maximum input images:** 4
- **Input image formats:** Not reported
- **Maximum input image size:** Not reported

## Example

```ts
import { experimental_generateImage as generateImage } from 'ai';

const result = await generateImage({
  model: 'bfl/flux-2-klein-4b',
  prompt: 'A red balloon on a wooden table.'
});
```

## About

Black Forest Labs released FLUX.2 [klein] 4B on January 15, 2026 as the entry point of the Klein family: compact image models Black Forest Labs positions for minimal latency. "Klein" is German for "small," reflecting the model's compact parameter footprint and minimal latency target.

The Apache 2.0 license separates Klein 4B from the rest of the FLUX family. Klein 9B carries the FLUX Non-Commercial License (NCL), and FLUX.2 Pro is a proprietary API model. Klein 4B places no commercial use restrictions on its weights. You can deploy it in commercial products, include it in open-source projects, and redistribute derivative works without seeking additional permission from Black Forest Labs.

The model unifies text-to-image generation, image-to-image editing, and multi-reference generation in a single checkpoint. Black Forest Labs describes Klein 4B as "compact but capable." The entire inference pipeline targets under 500 milliseconds.

## What to consider

Apache 2.0 licensing means you can incorporate Klein 4B weights into commercial products, fork them, modify them, and redistribute them. That's a meaningful distinction for teams with open-source or compliance requirements. Check N/A for the managed API.

## When to use

### Best For

- Commercial products and open-source projects where Apache 2.0 licensing is a legal or policy requirement. Klein 4B is the only FLUX.2 model with unrestricted commercial use rights
- Interactive design tools, live creative interfaces, and agentic visual loops where sub-second latency is a product requirement
- Workflows that call for text-to-image, image editing, and multi-reference generation from a single model

### Consider Alternatives When

- Maximum output quality is the goal. FLUX.2 Klein 9B or FLUX.2 Pro deliver higher fidelity
- The workload is masked region inpainting rather than generative or editing tasks. FLUX.1 Fill Pro is purpose-built for that

## Best for

- **Apache 2.0 licensing requirements:** Klein 4B is the only FLUX.2 model with unrestricted commercial use rights for commercial products and open-source projects
- **Sub-second latency:** Interactive design tools, live creative interfaces, and agentic visual loops where speed is a product requirement
- **One-model workflows:** Text-to-image, image editing, and multi-reference generation unified in a single checkpoint

## Consider alternatives

- **Maximum output quality:** FLUX.2 Klein 9B or FLUX.2 Pro deliver higher fidelity
- **Masked region inpainting:** FLUX.1 Fill Pro is purpose-built for mask-based fill rather than generative or editing tasks

## Frequently asked questions

### What does the Apache 2.0 license allow for FLUX.2 [klein] 4B?

Apache 2.0 permits unrestricted commercial use, modification, redistribution, and sublicensing of the model weights. Black Forest Labs adds no additional terms on top of the standard Apache 2.0 conditions. You can incorporate Klein 4B into commercial products or open-source projects without seeking separate permission.

### Is the Klein 4B available through AI Gateway the same as the open-weight release?

The API version is the step-distilled variant, optimized for inference speed. The undistilled Klein 4B Base is available as open weights for workflows that need the full training signal rather than minimum generation latency.

### What image tasks does FLUX.2 [klein] 4B support?

Klein 4B handles text-to-image (T2I), image-to-image editing (I2I), and multi-reference generation in a single unified model. You don't need separate checkpoints for different task types.

### How does Klein 4B differ from Klein 9B in terms of licensing?

Klein 4B is Apache 2.0, fully open for commercial and non-commercial use. Klein 9B is released under the FLUX Non-Commercial License, which restricts commercial deployment. For production commercial pipelines that need open licensing, Klein 4B is the appropriate choice.

### What does FLUX.2 [klein] 4B cost per image?

Current pricing is shown on this page. AI Gateway routes across providers, and rates may vary by provider.

## Links

- [Model page](https://vercel.com/ai-gateway/models/flux-2-klein-4b)
- [AI Gateway documentation](https://vercel.com/docs/ai-gateway)
- [Provider model documentation](https://bfl.ai/blog/flux2-klein-towards-interactive-visual-intelligence)
- [Provider pricing](https://bfl.ai/pricing)