Question 1

What is FLUX.2 Klein 4B?

Accepted Answer

FLUX.2 [klein] 4B is a compact 4-billion parameter image generation model from Black Forest Labs. It's distilled to just 4 inference steps for sub-second generation while maintaining high image quality. It uses a Mistral 3 VLM text embedder and supports up to 4 megapixel resolution.

Question 2

What license does Klein 4B use?

Accepted Answer

FLUX.2 [klein] 4B uses the Apache 2.0 license, making it fully available for commercial use with no restrictions. This is notable because the larger 9B variant uses a non-commercial license.

Question 3

How fast is Klein 4B compared to other FLUX models?

Accepted Answer

Klein 4B generates images in sub-second time thanks to step distillation (4 steps vs 25-50 for standard models). It's significantly faster than FLUX.2 Pro or FLUX.2 Max while trading some quality for speed — similar to FLUX.2 Flash but with a smaller footprint.

Question 4

Can Klein 4B do image editing?

Accepted Answer

Yes. Klein 4B unifies text-to-image generation and image editing in a single architecture. You can pass up to 4 reference images alongside your text prompt for guided generation, style transfer, or editing tasks. Use the edit endpoint for editing workflows.

Question 5

What resolution does Klein 4B support?

Accepted Answer

Klein 4B supports output up to 4 megapixels (e.g., 2048x2048). The recommended resolution is around 1-2 megapixels for optimal quality. All dimensions must be multiples of 16.

Question 6

What's the difference between Klein 4B and Klein 9B?

Accepted Answer

The 4B variant is smaller (13GB VRAM), Apache 2.0 licensed, and uses a Mistral 3 VLM text embedder. The 9B variant is larger (29GB VRAM), non-commercial licensed, uses an 8B Qwen3 text embedder, and produces slightly higher quality outputs with more diversity.

Question 7

How much does FLUX.2 Klein 4B cost on Runflow?

Accepted Answer

FLUX.2 Klein 4B costs $0.014 per megapixel for the first megapixel and $0.001 for each additional megapixel. A standard 1024x1024 image (~1MP) costs approximately $0.014.

black-forest-labs/flux-2-klein-4b

Related models

Start generating with FLUX.2 [klein] 4B