FLUX 3 Image

Klein

FLUX 3 Image Klein is a compact, open-weights version of FLUX 3 Image. It supports the same features: text to image, image editing, multi reference, and bounding boxes. It runs faster and fits on consumer GPUs, down to an RTX 3090.

Specs

FLUX 3 Image Klein comes in two variants. Distilled is step-distilled for fast inference. Base is the undistilled model for fine-tuning, LoRA training, and research.

	Klein (Distilled)	Klein Base
Parameters	5.6B	5.6B
Max resolution	Up to 4K	Up to 4K
Inference steps	16	50
Guidance (CFG)	1	3.5
Bounding box support	Yes	Yes
Best for	Fast generation, local deployment	Fine-tuning, LoRA training, research
License	FLUX Kommunity License	FLUX Kommunity License
Availability	API, Hugging Face	Hugging Face

Pricing

Priced per image by output resolution. Text to image and image editing cost the same.

Resolution	Price per image
768 × 768	$0.008
1K	$0.009
1.5K	$0.011
2K	$0.014
4K	$0.036

See API pricing for all models.

Ways to use it

API
Diffusers / Hugging Face
ComfyUI

Send a request to the Klein endpoint, then poll the returned polling_url until status is Ready. The request takes the same fields as FLUX 3 Image.

curl --request POST \
  --url https://api.bfl.ai/v1/flux-3-image-klein \
  --header "x-key: $BFL_API_KEY" \
  --header "Content-Type: application/json" \
  --data '{
  "prompt": "A red fox curled up asleep inside an open vintage leather suitcase on the luggage rack of an old wooden train compartment, soft window light falling on its fur, photorealistic.",
  "aspect_ratio": "4:3"
}'

See the API reference for all parameters.

Download the FLUX 3 Image Klein weights from Hugging Face and run them locally with Diffusers.

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 red fox curled up asleep inside an open vintage leather suitcase on the luggage rack "
        "of an old wooden train compartment, soft window light falling on its fur, photorealistic."
    ),
    generator=torch.Generator().manual_seed(0),
    output="images",
)[0]
image.save("klein.png")

For fine-tuning and LoRA training, use the Base weights (black-forest-labs/flux-3-image-klein-base).

Text to image

Photography, illustration, and typography from a single prompt. Click any image to view it full size.

Edit an image

Write the change as an instruction. Drag the handle to compare each source with its edit:

Train a LoRA

LoRA training lets you personalize Klein to your own brand guidelines, products, characters or visual styles. Train LoRAs on Klein Base. A rank-32 LoRA trained on a handful of images on a single GPU is enough to teach Klein a new style or edit. The trained LoRA can also run on Klein Distilled.

Diffusers

Hugging Face training scripts for DreamBooth and LoRA.

Training config

Setting	Value
Base model	Klein Base
Dataset	20 images, captions end with the trigger `shtm style`
Resolution	~1 MP, native aspect ratio
LoRA rank / alpha	32 / 32
Optimizer	AdamW, betas (0.9, 0.95)
Learning rate	1e-4, 200 warmup steps, then linear decay
Steps	4000, checkpoint every 250
Hardware	1 GPU, about 4.5 hours

Example: Persian miniature LoRA

We trained a style LoRA on 20 public-domain paintings from the 16th-century Shahnameh of Shah Tahmasp. Captions describe only the content and end with the trigger shtm style.Six of the 20 training images:

Training image: A crowned ruler in a green robe sits on a throne inside an ornate tiled palace hall, attended by courtiers and guards while musicians sit in the foreground. In a narrow panel at the right, grooms and soldiers stand among horses and decorated elephants in a flowering landscape. shtm style

Training image: A crowd of armored horsemen in bright coats and white turbans, carrying banners and a tall standard, ride their horses into a dark river. Two mounted men and two archers watch from the bank at upper left, a small figure sits in a boat at lower right, and a lion rests in the grass at lower left. shtm style

Training image: A man in a spotted yellow tunic, striped cap and red trousers stands among a herd of goats and antelope with curved horns. A large blaze of orange flames burns above him on a speckled ground, with an iris plant, a leafy tree and bright rocks around the edges. shtm style

Training image: A mounted nobleman in a plumed turban sits on a brown horse on a green hillside while attendants and riders crowd along the right edge. Hunters on foot and horseback chase deer, wolves, foxes and other animals among round bushes and rocky ridges, with a tent at the top and onlookers gathered in the lower left. shtm style

Training image: An armored warrior in a plumed white helmet wrestles a gray horned demon inside a dark cave, with blood and a severed leg beside them. Colorful rocky hills with blossoming trees surround the cave, small demons watch from the ridge above, and a standing attendant and a saddled horse wait at the right. shtm style

Training image: A bearded king sits cross-legged on a small round platform high on a rocky ledge beside a waterfall. Crowds of robed men and attendants gather on the hillsides below, and animals roam the green thicket in the foreground among twisting trees and flowering rocks. shtm style

Example caption:

A crowned ruler in a green robe sits on a throne inside an ornate tiled palace hall, attended by courtiers and guards while musicians sit in the foreground. In a narrow panel at the right, grooms and soldiers stand among horses and decorated elephants in a flowering landscape. shtm style

Base vs. LoRA at step 1500, same prompt and seed.

Run a LoRA on Klein Distilled

Klein Base and Klein Distilled share the same architecture, so a LoRA trained on Base loads into Distilled without any conversion. Train on Base, then generate with Distilled at 16 steps instead of 50.Keep Distilled’s sampler settings and lower the LoRA scale slightly. In our tests 0.75 matched the Base + LoRA result most closely, and anything from 0.5 to 1.0 works.

Setting	Value
Steps	16
Guidance (CFG)	1
LoRA scale	0.75 (0.5 to 1.0)

The style or edit comes through as strongly as on Base. Distilled renders the same seed differently, so expect small changes in details like a hair color or the phase of the moon, not in the style itself.Two style LoRAs trained on Base, run on Base at 50 steps and on Distilled at 16 steps. Same prompt and seed.

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Legacy Models

FLUX 3 Image Klein

Klein

Specs

Pricing

Ways to use it

Text to image

Edit an image

Train a LoRA

Diffusers

Training config

Example: Persian miniature LoRA

Run a LoRA on Klein Distilled

​Klein

​Specs

​Pricing

​Ways to use it

​Text to image

​Edit an image

​Train a LoRA

Diffusers

​Training config

​Example: Persian miniature LoRA

​Run a LoRA on Klein Distilled

Klein

Specs

Pricing

Ways to use it

Text to image

Edit an image

Train a LoRA

Training config

Example: Persian miniature LoRA

Run a LoRA on Klein Distilled