flux-3-image-klein-pup: What's New, Hardware Needed, How to Run It Free

FLUX 3 Image Klein Prompt Upsampler turns a short request into a full-length prompt for the FLUX 3 image model. It even accepts up to ten reference images and optional bounding boxes.

FLUX 3 Image Klein Prompt Upsampler is a 9.4 billion-parameter vision-language model. It takes a brief description, a set of reference pictures, and optionally a JSON list of bounding boxes, then returns a single caption that contains scene, lighting, camera angle, subject details and exact box references. The caption is ready to feed straight into the FLUX 3 Image Klein generator, whether you are doing text-to-image, image-to-image editing, or layout-guided generation.

According to Black-forest, the upsampler is a full fine-tune of Qwen3.5-9B with the vision tower frozen. Training happened in two stages: first on pairs of short requests and their expanded prompts, then on preference data where the model’s own prompts were ranked after rendering with FLUX 3 Image Klein. The result is a model that knows exactly which details the image generator needs, without extra system prompting.

The biggest strength is that the output prompt already contains medium, style, lighting, camera angle and per-subject attributes, so the image model can produce high-quality results without generic defaults. Bounding-box coordinates are kept verbatim, letting you control placement precisely. Limits include English-only prompts, and reference images are resized to at most one megapixel, which can cause loss of tiny details. The model does not refuse requests, so external safety checks are recommended.

If you already run FLUX 3 Image Klein locally, this upsampler is a natural companion. It fits on a RTX 4060 in 4-bit mode, using about 8 GB of memory, and runs at roughly 45 tokens per second on a RTX 3060 with 12 GB VRAM. Faster cards reach up to 190 tokens per second.

What do you need to run it at home? At 4-bit it takes about 8 gigabytes of memory. The smallest home machine that holds it fully is an RTX 4060. On an RTX 3060 12 GB with 32 gigabytes of RAM it writes about 45 tokens per second. On an RTX 4090 with 64 gigabytes of RAM it writes about 116 tokens per second.

There is no free API for it yet. The weights are open: you can download them from Hugging Face under the Apache 2.0 license. Arena has not ranked it yet: we add the score as soon as the votes arrive.

Compare flux 3 image klein pup with every free model, and check what your own GPU can run, on FreeLLMArena.