FLUX.1 Model Guide

Overview

FLUX.1 is Black Forest Labs’ state-of-the-art text-to-image generation model, representing the cutting edge of diffusion model technology. It delivers exceptional image quality, outstanding prompt adherence, and remarkable detail in generated images.

FLUX.1 Dev

Best for: Production use, highest quality

Superior image quality
Excellent prompt following
Requires 16GB+ VRAM

FLUX.1 Schnell

Best for: Fast iteration, prototyping

Optimized for speed (1-4 steps)
Good quality/speed tradeoff
Requires 12GB+ VRAM

Model Variants

FLUX.1 Dev

The development variant optimized for the highest quality outputs.

from hypergen import model

m = model.load("black-forest-labs/FLUX.1-dev", torch_dtype="bfloat16")
m.to("cuda")

Key Features:

Quality: State-of-the-art image generation
Prompt Following: Excellent text comprehension
License: Non-commercial (requires license for commercial use)
VRAM: 16GB+ recommended

FLUX.1 Schnell

The “schnell” (fast) variant optimized for rapid generation.

from hypergen import model

m = model.load("black-forest-labs/FLUX.1-schnell", torch_dtype="bfloat16")
m.to("cuda")

Key Features:

Speed: 3-4x faster than Dev
Quality: Excellent (slightly below Dev)
License: Apache 2.0 (permissive, commercial-friendly)
VRAM: 12GB+ recommended

Loading FLUX.1 with HyperGen

Basic Loading

from hypergen import model

# Load FLUX.1 Dev
m = model.load("black-forest-labs/FLUX.1-dev", torch_dtype="bfloat16")
m.to("cuda")

# Generate an image
image = m.generate("A serene mountain landscape at sunset")
image[0].save("output.png")

Always use bfloat16 dtype with FLUX.1 for optimal quality and memory efficiency. The model was trained with bfloat16 precision.

Advanced Loading Options

from hypergen import model

# Load with custom configuration
m = model.load(
    "black-forest-labs/FLUX.1-dev",
    torch_dtype="bfloat16",
    variant="bf16",              # Use bfloat16 weights
    use_safetensors=True,        # Use safetensors format
)
m.to("cuda")

# Enable memory optimizations (for lower VRAM)
m.enable_model_cpu_offload()    # Offload to CPU when not in use
m.enable_vae_slicing()           # Process VAE in slices

Low VRAM Configuration

For systems with limited VRAM (12GB):

from hypergen import model

m = model.load("black-forest-labs/FLUX.1-schnell", torch_dtype="bfloat16")
m.to("cuda")

# Enable memory optimizations
m.enable_model_cpu_offload()
m.enable_vae_slicing()
m.enable_attention_slicing()

Training LoRAs with FLUX.1

FLUX.1 supports efficient LoRA fine-tuning with HyperGen’s optimized training pipeline.

Basic LoRA Training

from hypergen import model, dataset

# Load model
m = model.load("black-forest-labs/FLUX.1-dev", torch_dtype="bfloat16")
m.to("cuda")

# Load training data
ds = dataset.load("./my_training_images")

# Train LoRA
lora = m.train_lora(
    ds,
    steps=1500,
    rank=32,
    alpha=64,
    learning_rate=5e-5,
)

Recommended Training Parameters

Style Transfer
Subject/Character
Concept

Goal: Learn an artistic style or aesthetic

lora = m.train_lora(
    ds,
    steps=1500,
    learning_rate=5e-5,
    rank=32,
    alpha=64,
    batch_size=1,
    gradient_accumulation_steps=4,
)

Dataset Requirements:

50-200 images
Consistent style across images
Captions describing content, not style

Goal: Learn a specific person, character, or object

lora = m.train_lora(
    ds,
    steps=2000,
    learning_rate=4e-5,
    rank=64,
    alpha=128,
    batch_size=1,
    gradient_accumulation_steps=4,
)

Dataset Requirements:

20-100 images
Variety of poses and angles
Detailed captions describing poses, clothing, expressions

Goal: Learn a new concept or composition style

lora = m.train_lora(
    ds,
    steps=2500,
    learning_rate=5e-5,
    rank=48,
    alpha=96,
    batch_size=1,
    gradient_accumulation_steps=8,
)

Dataset Requirements:

30-150 images
Variety of examples
Captions focusing on composition and elements

Memory-Optimized Training

For 16GB VRAM GPUs:

lora = m.train_lora(
    ds,
    steps=1500,
    learning_rate=5e-5,
    rank=32,                        # Medium capacity
    alpha=64,
    batch_size=1,                   # Single image per step
    gradient_accumulation_steps=8,  # Simulate batch_size=8
    save_steps=500,
    output_dir="./flux_lora_checkpoints"
)

High-Quality Training

For 24GB+ VRAM GPUs:

lora = m.train_lora(
    ds,
    steps=2500,
    learning_rate=4e-5,
    rank=64,                        # High capacity
    alpha=128,
    batch_size=2,                   # Process 2 images at once
    gradient_accumulation_steps=4,  # Simulate batch_size=8
    save_steps=500,
    output_dir="./flux_lora_checkpoints"
)

Inference Parameters

Generation Settings

image = m.generate(
    prompt="A photo of a cat wearing a space suit on Mars",
    num_inference_steps=50,      # 20-50 for Dev, 1-4 for Schnell
    guidance_scale=7.5,          # Prompt adherence strength
    height=1024,                 # Image height
    width=1024,                  # Image width
    num_images=4,                # Generate 4 images
    seed=42,                     # For reproducibility
)

Recommended Parameters

FLUX.1 Dev

Quality Priority:

num_inference_steps=50
guidance_scale=7.5

Balanced:

num_inference_steps=30
guidance_scale=7.0

Speed Priority:

num_inference_steps=20
guidance_scale=6.5

FLUX.1 Schnell

Best Settings:

num_inference_steps=4
guidance_scale=0.0  # Schnell doesn't use CFG

Alternative:

num_inference_steps=2
guidance_scale=0.0

Advanced Generation

# Generate with custom scheduler
from diffusers import DPMSolverMultistepScheduler

m.scheduler = DPMSolverMultistepScheduler.from_config(m.scheduler.config)

image = m.generate(
    prompt="A futuristic cityscape at night",
    negative_prompt="blurry, low quality, distorted",
    num_inference_steps=30,
    guidance_scale=7.5,
    height=1024,
    width=1024,
)

Performance Benchmarks

Generation Benchmarks

Based on NVIDIA RTX 4090, 1024x1024 images:

Variant	Steps	VRAM Used	Time	Quality
FLUX.1 Dev	50	~18GB	~8s	Outstanding
FLUX.1 Dev	30	~18GB	~5s	Excellent
FLUX.1 Dev	20	~18GB	~3.5s	Very Good
FLUX.1 Schnell	4	~16GB	~1.5s	Excellent
FLUX.1 Schnell	2	~16GB	~1s	Very Good

Training Benchmarks

LoRA training on RTX 4090, 50 images, rank 32:

Configuration	VRAM	Time (1000 steps)	Time (2000 steps)
Batch 1, GA 1	~16GB	~20 min	~40 min
Batch 1, GA 4	~16GB	~22 min	~44 min
Batch 1, GA 8	~16GB	~25 min	~50 min
Batch 2, GA 4	~22GB	~28 min	~56 min

GA = Gradient Accumulation Steps. Higher values slightly increase training time but improve quality.

GPU Requirements

Minimum (Schnell)

VRAM: 12GBExamples:

RTX 3060 (12GB)
RTX 4070
A10

Settings:

Enable optimizations
Batch size 1
Rank 16-32

Recommended (Dev)

VRAM: 16GBExamples:

RTX 4080
RTX 4090
A100 (40GB)

Settings:

Standard settings
Batch size 1-2
Rank 32-64

Optimal (Dev)

VRAM: 24GB+Examples:

RTX 4090
A100 (40GB)
H100

Settings:

Maximum quality
Batch size 2-4
Rank 64-128

Best Practices

Prompt Engineering

FLUX.1 has excellent prompt comprehension. Here are tips for best results:

Structure
Details
Style Control
Text in Images

Good prompt structure:

[Subject] [Action/Pose] [Environment] [Lighting] [Style] [Quality]

Example:

prompt = """
A majestic red fox sitting on a moss-covered rock in a misty forest,
soft morning light filtering through the trees, photorealistic style,
highly detailed, 8k quality
"""

Control artistic style:

# Photorealistic
prompt = "A portrait of a woman, photorealistic, professional photography, 85mm lens"

# Artistic
prompt = "A landscape painting in the style of Claude Monet, impressionist, oil on canvas"

# Digital Art
prompt = "A futuristic robot, digital art, concept art, trending on ArtStation"

FLUX.1 can generate text:

prompt = 'A cat holding a sign that says "HELLO WORLD" in bold letters'

Tips for text generation:

Put text in quotes
Specify font style if needed
Keep text relatively short
Describe the sign/banner/object containing text

Training Best Practices

Dataset Preparation

Quality over quantity:

Use high-resolution images (1024x1024 or higher)
Ensure consistent quality across dataset
20-150 images is usually sufficient
Remove duplicates and near-duplicates

Caption Quality

Write descriptive captions:

Describe what you see, not what you want to learn
Include details about composition, lighting, colors
Be consistent in caption style
Use natural language

Example:

A close-up portrait of a person wearing a red jacket,
standing in front of a blue wall, soft natural lighting
from the left, neutral expression

Hyperparameter Tuning

Start with defaults, then adjust:

Begin with recommended settings
If underfitting (not learning), increase:
- Training steps
- LoRA rank
- Learning rate (carefully)
If overfitting (memorizing), decrease:
- Training steps
- LoRA rank
- Add more training images

Monitor Training

Save checkpoints regularly:

lora = m.train_lora(
    ds,
    steps=2000,
    save_steps=500,  # Save every 500 steps
    output_dir="./checkpoints"
)

Test different checkpoints to find the best one.

Memory Optimization

Enable Model CPU Offload

Offload model components to CPU when not in use:

m.enable_model_cpu_offload()

Pros: Reduces VRAM by 40-50% Cons: Slower generation (10-20% slower)

Enable VAE Slicing

Process VAE in smaller slices:

m.enable_vae_slicing()

Pros: Reduces VRAM by 10-15% Cons: Minimal performance impact

Enable Attention Slicing

Compute attention in slices:

m.enable_attention_slicing()

Pros: Reduces VRAM by 15-20% Cons: Slower generation (5-10% slower)

Use Lower Rank

Reduce LoRA rank during training:

lora = m.train_lora(ds, rank=16, alpha=32)  # Instead of rank=32

Pros: Reduces VRAM by 20-30% Cons: Lower model capacity

Troubleshooting

Common Issues

Out of Memory During Generation

Solutions:

Enable memory optimizations:

m.enable_model_cpu_offload()
m.enable_vae_slicing()
m.enable_attention_slicing()

Reduce image resolution:

image = m.generate(prompt, height=768, width=768)

Generate fewer images at once:

image = m.generate(prompt, num_images=1)  # Instead of 4

Out of Memory During Training

Solutions:

Reduce batch size:
lora = m.train_lora(ds, batch_size=1)

Lower LoRA rank:

lora = m.train_lora(ds, rank=16, alpha=32)

Use gradient accumulation:

lora = m.train_lora(ds, batch_size=1, gradient_accumulation_steps=8)

Poor Training Results

Possible causes and solutions:

Not enough training steps:
- Increase to 2000-3000 steps
Low quality dataset:
- Use higher resolution images
- Add more diverse examples
- Improve caption quality
Wrong hyperparameters:
- Try learning_rate=4e-5 or 6e-5
- Increase rank to 64
- Adjust alpha to 2x rank

Slow Generation Speed

Solutions:

Use FLUX.1 Schnell instead of Dev:

m = model.load("black-forest-labs/FLUX.1-schnell", torch_dtype="bfloat16")

Reduce inference steps:

image = m.generate(prompt, num_inference_steps=20)

Disable CPU offload if enabled:
m.disable_model_cpu_offload()

Example Projects

Portrait LoRA Training

from hypergen import model, dataset

# Load FLUX.1 Dev
m = model.load("black-forest-labs/FLUX.1-dev", torch_dtype="bfloat16")
m.to("cuda")

# Load portrait dataset
ds = dataset.load("./portraits", caption_extension=".txt")

# Train portrait LoRA
lora = m.train_lora(
    ds,
    steps=2000,
    learning_rate=4e-5,
    rank=64,
    alpha=128,
    batch_size=1,
    gradient_accumulation_steps=4,
    save_steps=500,
    output_dir="./portrait_lora"
)

print("Training complete! LoRA saved to ./portrait_lora")

Style Transfer LoRA

from hypergen import model, dataset

# Load FLUX.1 Dev
m = model.load("black-forest-labs/FLUX.1-dev", torch_dtype="bfloat16")
m.to("cuda")

# Load artistic style dataset
ds = dataset.load("./art_style")

# Train style LoRA with lower rank (style doesn't need high capacity)
lora = m.train_lora(
    ds,
    steps=1500,
    learning_rate=5e-5,
    rank=32,
    alpha=64,
    batch_size=1,
    gradient_accumulation_steps=8,
    output_dir="./style_lora"
)

Batch Generation

from hypergen import model

# Load FLUX.1 Schnell for fast generation
m = model.load("black-forest-labs/FLUX.1-schnell", torch_dtype="bfloat16")
m.to("cuda")

# Generate multiple variations
prompts = [
    "A serene mountain landscape at sunrise",
    "A bustling city street at night",
    "A peaceful garden with cherry blossoms",
    "A dramatic ocean sunset with waves",
]

for i, prompt in enumerate(prompts):
    images = m.generate(
        prompt,
        num_inference_steps=4,
        guidance_scale=0.0,
        num_images=2,
    )

    for j, img in enumerate(images):
        img.save(f"output_{i}_{j}.png")

print("Generated", len(prompts) * 2, "images")

License Information

Important: FLUX.1 variants have different licenses!

FLUX.1 Dev

License: FLUX.1 Dev Non-Commercial License

Personal use
Research
Evaluation
L Commercial use (requires separate license)

Contact Black Forest Labs for commercial licensing.

FLUX.1 Schnell

License: Apache 2.0

Personal use
Research
Commercial use
Modification and distribution

Fully permissive open-source license.

Next Steps

Training Guide

Complete LoRA training documentation

Dataset Preparation

Learn how to prepare training data

Serving FLUX.1

Deploy FLUX.1 with the API

API Reference

Complete model API documentation

​Overview

FLUX.1 Dev

FLUX.1 Schnell

​Model Variants

​FLUX.1 Dev

​FLUX.1 Schnell

​Loading FLUX.1 with HyperGen

​Basic Loading

​Advanced Loading Options

​Low VRAM Configuration

​Training LoRAs with FLUX.1

​Basic LoRA Training

​Recommended Training Parameters

​Memory-Optimized Training

​High-Quality Training

​Inference Parameters

​Generation Settings

​Recommended Parameters

FLUX.1 Dev

FLUX.1 Schnell

​Advanced Generation

​Performance Benchmarks

​Generation Benchmarks

​Training Benchmarks

​GPU Requirements

Minimum (Schnell)

Recommended (Dev)

Optimal (Dev)

​Best Practices

​Prompt Engineering

​Training Best Practices

​Memory Optimization

​Troubleshooting

​Common Issues

​Example Projects

​Portrait LoRA Training

​Style Transfer LoRA

​Batch Generation

​License Information

​FLUX.1 Dev

​FLUX.1 Schnell

​Next Steps

Training Guide

Dataset Preparation

Serving FLUX.1

API Reference

​Additional Resources

Overview

Model Variants

FLUX.1 Dev

FLUX.1 Schnell

Loading FLUX.1 with HyperGen

Basic Loading

Advanced Loading Options

Low VRAM Configuration

Training LoRAs with FLUX.1

Basic LoRA Training

Recommended Training Parameters

Memory-Optimized Training

High-Quality Training

Inference Parameters

Generation Settings

Recommended Parameters

Advanced Generation

Performance Benchmarks

Generation Benchmarks

Training Benchmarks

GPU Requirements

Best Practices

Prompt Engineering

Training Best Practices

Memory Optimization

Troubleshooting

Common Issues

Example Projects

Portrait LoRA Training

Style Transfer LoRA

Batch Generation

License Information

FLUX.1 Dev

FLUX.1 Schnell

Next Steps

Additional Resources