Black Forest Labs released both Flux 2 Dev and Flux 2 Klein as part of their January 2025 FLUX.2 family. While they share the same architectural DNA, they target very different use cases. Dev is the full 12-billion parameter open-weight model designed for maximum quality. Klein is a distilled 4-billion parameter variant optimized for speed and cost efficiency.
The naming reflects the philosophy: "Klein" means "small" in German. Black Forest Labs (headquartered in Germany) designed Klein to democratize access to their technology—delivering solid results at a fraction of the computational cost. Klein costs roughly 6x less per image than Dev.
Speed is Klein's other advantage. With sub-second generation times compared to Dev's ~2.5 seconds, Klein enables real-time applications and rapid iteration that Dev simply cannot match. For workflows where you need to generate hundreds or thousands of images, this difference compounds dramatically.
The quality gap is real but manageable. ELO scores show Dev at ~1143 versus Klein's ~1066—a noticeable difference in blind comparisons. But for many practical applications, especially at web resolutions, Klein's output quality remains more than acceptable. The question is whether your use case demands Dev's refinement or can benefit from Klein's efficiency.
Note: Klein is available in multiple variants (4B, 4B Distilled, 9B). This comparison uses the base 4B model, the most cost-effective option.