SD-Next/flux-3-image-klein

FLUX 3 Image Klein (SD.Next Mirror)

Mirror of black-forest-labs/flux-3-image-klein at revision 8454017f, kept for use with SD.Next. Please find the original repository here.

• Transformer, VAE, text encoder and the BFL single-file checkpoint are unchanged from the original repository; the quantized variants folder is not included.
• License: FLUX Kommunity License (see LICENSE.md and NOTICE.md).

Loads in SD.Next from the Models reference list, or with diffusers modular pipelines.

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FLUX 3 Image Klein

FLUX 3 Image Klein is a 5.6B open weights model for text-to-image generation and image editing. It takes a prompt and up to 10 reference images and returns one image. Text-to-image, single-reference edits and multi-reference compositions run through the same model, with Qwen3-VL-4B-Instruct as the text encoder.

The 5.6B parameter label refers to the image transformer; the text encoder is separate.

This repository holds the distilled checkpoint for generation and image editing. For fine-tuning, LoRA training and research, use FLUX 3 Image Klein Base.

Inference code, prompt upsampling and the bounding box format: black-forest-labs/flux-3-image-klein on GitHub.

This repository includes the BF16 transformer and FP8 and NVFP4 variants, together with the Qwen3-VL-4B-Instruct text encoder and image autoencoder.

Checkpoint	Format	Steps	Guidance	Built for
Klein Base	undistilled, bfloat16	50	3.5	fine-tuning, LoRA training, research
Klein	distilled, bfloat16	16	none	generation and editing, self-hosting; the checkpoint behind the BFL API

Key Features

1. Text-to-image, single-reference editing and multi-reference generation in one model.
2. Bounding boxes in the prompt. Place elements with boxes on a 0 to 1000 grid, then recolor, move, replace or remove them through the prompt. Boxes guide placement and scale; they do not constrain pixels to a hard mask.
3. Text rendering within generated images.
4. Released under the FLUX Kommunity License. The license permits non-commercial use and provides a commercial-output exception for Qualifying Users, subject to its terms. See License below.

Download

Download the root BF16 distilled package, including its text encoder and image autoencoder, without downloading the quantized variants:

from huggingface_hub import snapshot_download

snapshot_download(
    repo_id="black-forest-labs/flux-3-image-klein",
    local_dir="weights/flux-3-image-klein",
    allow_patterns=[
        "model.safetensors", "config.json", "manifest.json",
        "ae.safetensors", "text_encoder/*",
        "README.md", "LICENSE.md", "NOTICE.md",
    ],
)

To download a quantized distilled transformer instead, replace the three root transformer patterns (model.safetensors, config.json, and manifest.json) with variants/fp8r/* or variants/nvfp4/*. Keep ae.safetensors and text_encoder/* for the other components.

These files contain the model package, not a complete inference application. Use an inference implementation that supports flow-map sampling and this checkpoint format. Quantized packages need a loader that supports their format; their file size is not a measure of total GPU memory use.

Using with reference code

The distilled checkpoint is served on the BFL API as FLUX 3 Image Klein. The reference inference code is black-forest-labs/flux-3-image-klein.

From the reference implementation checkout, install the package and download the two components the CLI loads besides this checkpoint. The CLI reads its weights from weights/ (set WEIGHTS_DIR for another root), where the download above puts this repository.

pip install -e .

# safety classifier, always loaded
hf download Falconsai/nsfw_image_detection --local-dir weights/nsfw-classifier
# prompt upsampler (18.8 GB), rewrites the prompt first; skip it and add --no-pup to send prompts as typed
hf download black-forest-labs/flux-3-image-klein-pup --local-dir weights/pup

# text-to-image
python scripts/cli.py "A wide-angle photograph of a lone American bison in a misty geothermal landscape, half hidden by white steam, a slate-blue stream and evergreens fading into the mist behind. Muted, cool palette, soft overcast light." \
  --model distilled --out bison.png

# image editing; repeat --image for multiple references
python scripts/cli.py "The same lone American bison in the same misty geothermal landscape, now at night under a full moon: the steam lit from behind, cool blue light, deep shadows, stars above the evergreens." \
  --model distilled --image bison.png --out bison_night.png

Using with Diffusers

FLUX 3 Image Klein uses a modular pipeline. Pass prompt for text-to-image generation, or pass image with a prompt for editing. image can be one image or a list of reference images.

pip install git+https://github.com/huggingface/diffusers.git

import torch
from diffusers import ModularPipeline

pipe = ModularPipeline.from_pretrained("black-forest-labs/flux-3-image-klein")
pipe.load_components(dtype=torch.bfloat16)
pipe.to("cuda")

image = pipe(
    prompt="A wide-angle photograph of a lone American bison in a misty geothermal landscape, half hidden by white steam, a slate-blue stream and evergreens fading into the mist behind. Muted, cool palette, soft overcast light.",
    generator=torch.Generator().manual_seed(0),
    output="images",
)[0]
image.save("bison.png")

night = pipe(
    prompt="The same lone American bison in the same misty geothermal landscape, now at night under a full moon: the steam lit from behind, cool blue light, deep shadows, stars above the evergreens.",
    image=image,
    generator=torch.Generator().manual_seed(0),
    output="images",
)[0]
night.save("bison_night.png")

Prompt upsampling

The reference CLI runs a prompt upsampler before every generation: it turns a short request, together with the reference images when editing, into the full scene caption the model wants. With Diffusers it is a separate model, black-forest-labs/flux-3-image-klein-pup. Run it with Transformers and pass its output to the pipeline above as prompt:

import json

from huggingface_hub import hf_hub_download
from transformers import AutoProcessor, Qwen3_5ForConditionalGeneration

pup_id = "black-forest-labs/flux-3-image-klein-pup"
processor = AutoProcessor.from_pretrained(pup_id)
upsampler = Qwen3_5ForConditionalGeneration.from_pretrained(pup_id, dtype=torch.bfloat16, device_map="auto").eval()
system_prompts = json.load(open(hf_hub_download(pup_id, "system_prompts.json")))


def upsample(prompt, images=()):
    if images:
        text = (
            "Reference images follow in order (the first image, the second image, ...).\n"
            f"User request: {prompt}\nOutput the caption."
        )
        content = [{"type": "image", "image": image} for image in images] + [{"type": "text", "text": text}]
        messages = [{"role": "system", "content": system_prompts["i2i"]}, {"role": "user", "content": content}]
    else:
        messages = [{"role": "system", "content": system_prompts["t2i"]}, {"role": "user", "content": prompt}]
    inputs = processor.apply_chat_template(
        messages, add_generation_prompt=True, tokenize=True, return_dict=True, return_tensors="pt", enable_thinking=False
    ).to(upsampler.device)
    with torch.no_grad():
        output = upsampler.generate(**inputs, max_new_tokens=3584, do_sample=False)
    return processor.decode(output[0, inputs["input_ids"].shape[1]:], skip_special_tokens=True).strip()


image = pipe(prompt=upsample("A bison in a misty geothermal landscape"), output="images")[0]

For an edit, pass the same reference images to both: pipe(prompt=upsample(instruction, [image]), image=image, ...). The upsampler also writes the layout captions from a list of boxes; see its model card.

Prompting

The caption controls composition; reference images anchor content, they do not lock structure.

• Write full scene captions: framing, subject, background, lighting. A short prompt gives generic output, and a one-line edit instruction ("make it blue") reframes the shot. The prompt upsampler writes the caption from a short request.
• For edits, describe the target image as a complete caption of the reference with the edit folded in, or let the prompt upsampler write it from the instruction and the references. For style, describe the attributes (palette, stroke, texture) rather than naming an artwork.
• For layout, append a JSON list of elements to the caption. Each box is [top, left, bottom, right] on a 0 to 1000 grid; tag the element in the caption with <id>:

Minimalist graphic illustration featuring a black silhouette of a person <silhouette_1> centered against a solid, vibrant chartreuse background <background_1>. The figure is captured in a dynamic, mid-stride running pose, facing toward the left side of the frame. [{"id": "background_1", "bbox": [0, 0, 1000, 1000], "desc": "A flat field of neon yellow-green with a subtle paper texture and fine, organic grain."}, {"id": "silhouette_1", "bbox": [150, 150, 850, 850], "desc": "A black silhouette of a person in motion, made of dense stippled ink."}]

For edits by box, refer to the n-th reference as <ref_image_n> and give each element from, src_bbox and tgt_bbox; a null target removes it. The full format with worked examples: Bounding boxes.

Limitations

• This model is not intended or able to provide factual information.
• While the model can output text, text rendered may be inaccurate or subject to distortion.
• As a statistical model, this checkpoint may represent or amplify biases observed in the training data.
• The model may fail to generate output that matches the prompts.
• Prompt following is heavily influenced by the prompting style. Short prompts produce generic output.
• Boxes set placement and scale, not a hard mask: an element can extend past its box, and small requested elements may not appear. Edits can change content outside the requested region.

Hardware

Peak GPU memory with the reference code, B200, 1024x1024, prompt upsampler off: 31 GB in BF16, 26 GB in FP8, 25 GB in NVFP4. The prompt upsampler adds about 28 GB on an 80 GB GPU.

Out-of-scope use

See Section 4 of the FLUX Kommunity License for the full restrictions. They include military purposes; surveillance, including related research and development; biometric processing; unlawful, unsafe, fraudulent, defamatory, or abusive activity; generating unlawful content, including child sexual abuse material or non-consensual intimate images; violating third-party rights, including rights of publicity or digital replica rights; and using the model, its Derivatives, or its Outputs to improve another AI model that performs a function similar to a FLUX Model or Derivative.

The license also covers export controls and sanctions. Its commercial-use exception is not blanket permission for commercial fine-tuning or distribution. Consult the full license for the terms that apply to each use.

Nothing contained in this model card should be interpreted as or deemed a restriction or modification to the license the model is released under.

Responsible AI Development

Black Forest Labs is committed to responsible model development and deployment. Prior to releasing FLUX 3 Image Klein, we evaluated and mitigated a number of risks, including child sexual abuse material (CSAM) and nonconsensual intimate imagery (NCII). For detailed information about our mitigations, evaluation processes, content provenance features, and policies, please see our post: Capable, Open, and Safe: Combating AI Misuse. To report safety concerns, contact safety@blackforestlabs.ai.

License

This model is released under the FLUX Kommunity License v.1.0: non-commercial use, plus commercial output generation by Qualifying Users with less than US$5M in gross annualized revenue, including affiliates, subject to the license terms. For other uses, see commercial licensing.

The Qwen3-VL-4B-Instruct text encoder is under Apache-2.0.

Trademarks and IP

Use of Black Forest Labs and FLUX trademarks requires prior written permission, except for required attribution or necessary descriptive references. Use must not cause confusion or imply sponsorship or endorsement. Third-party trademarks remain subject to their owners' policies.

Citation

If you use FLUX 3 Image in your work, please cite:

@misc{bfl2026flux3image,
  author       = {{Black Forest Labs}},
  title        = {{FLUX} 3 Image Klein},
  year         = {2026},
  url          = {https://bfl.ai/blog/flux-3-image-klein},
}