flux-txt2img

Flux Text-to-Image Workflows

Overview

Flux is a guidance-distilled diffusion model family from Black Forest Labs. It uses a separate FluxGuidance node instead of KSampler CFG (which must always be 1.0). Three variants are available locally:

1. Flux.1 Dev SRPO — Fine-tuned Flux.1 Dev with SRPO alignment. Uses DualCLIPLoader (T5XXL + CLIP-L). BF16 only.
2. Flux 2 Klein 9B — Distilled Flux 2 variant. Uses single CLIPLoader (Qwen3-8B) + flux2-vae.safetensors. Fast 4-step generation.
3. Flux 2 Turbo LoRA — Applied to Flux.1 Dev for 4-step generation.

Models

Flux.1 Dev SRPO

Flux 2 Klein 9B

Klein 9B vs Flux.1 Dev: Klein uses Qwen3-8B text encoder (not T5XXL + CLIP-L). It has a different VAE (flux2-vae.safetensors). 9B distilled runs in 4 steps; 9B base needs ~50 steps at CFG 5.0. Fits in ~20GB VRAM with FP8.

Flux 2 Turbo LoRA (applied to Flux.1 Dev)

Conditioning

CLIPTextEncodeFlux (Recommended for Flux.1 Dev)

Provides separate prompt fields for each text encoder:

{
  "class_type": "CLIPTextEncodeFlux",
  "inputs": {
    "clip": ["<dual_clip>", 0],
    "clip_l": "short prompt for CLIP-L",
    "t5xxl": "detailed description for T5XXL",
    "guidance": 3.5
  }
}

clip_l captures key semantic features. t5xxl expands and refines descriptions. For simple use, put the same prompt in both fields. Guidance is built into this node — no separate FluxGuidance needed.

FluxGuidance (Alternative)

If using standard CLIPTextEncode instead of CLIPTextEncodeFlux, apply guidance separately:

{
  "class_type": "FluxGuidance",
  "inputs": {
    "conditioning": ["<clip_text_encode>", 0],
    "guidance": 3.5
  }
}

Guidance Values

Negative Conditioning

Flux does NOT support traditional negative prompts (guidance-distilled, CFG=1.0). Use ConditioningZeroOut:

{
  "class_type": "ConditioningZeroOut",
  "inputs": { "conditioning": ["<positive_cond>", 0] }
}

Or simply use an empty CLIPTextEncode for the negative input.

Sampler Settings

Flux.1 Dev SRPO

SRPO note: The ipndm/beta combo is specifically recommended by the SRPO author. Standard Flux settings (euler/simple) also work but ipndm/beta gives better results with this fine-tune.

Flux 2 Klein 9B (Distilled)

Flux 2 Klein 9B (Base/Undistilled)

Flux.1 Dev + Turbo LoRA

Resolutions

Flux operates at ~1 megapixel natively. Dimensions should be multiples of 8.

Prompt Style

Natural language descriptions. No quality tags needed (unlike SDXL/Illustrious). Detailed, descriptive prompts work best.

Good: "A young woman with auburn hair sits at a sunlit cafe in Paris, wearing a cream linen blazer, soft bokeh background, shot on Sony A7III 85mm f/1.4"
Bad: "masterpiece, best quality, 1girl, cafe, paris"

Complete Workflow: Flux.1 Dev SRPO

{
  "1": { "class_type": "UNETLoader", "inputs": { "unet_name": "flux.1-dev-SRPO-BFL-bf16.safetensors", "weight_dtype": "default" }},
  "2": { "class_type": "DualCLIPLoader", "inputs": { "clip_name1": "t5xxl_fp8_e4m3fn.safetensors", "clip_name2": "clip_l.safetensors", "type": "flux" }},
  "3": { "class_type": "VAELoader", "inputs": { "vae_name": "ae.safetensors" }},
  "4": { "class_type": "CLIPTextEncodeFlux", "inputs": {
    "clip": ["2", 0],
    "clip_l": "<short prompt>",
    "t5xxl": "<detailed prompt>",
    "guidance": 3.5
  }},
  "5": { "class_type": "ConditioningZeroOut", "inputs": { "conditioning": ["4", 0] }},
  "6": { "class_type": "EmptyLatentImage", "inputs": { "width": 896, "height": 1152, "batch_size": 1 }},
  "7": { "class_type": "KSampler", "inputs": {
    "model": ["1", 0],
    "positive": ["4", 0],
    "negative": ["5", 0],
    "latent_image": ["6", 0],
    "seed": 42, "steps": 20, "cfg": 1, "sampler_name": "ipndm", "scheduler": "beta", "denoise": 1
  }},
  "8": { "class_type": "VAEDecode", "inputs": { "samples": ["7", 0], "vae": ["3", 0] }},
  "9": { "class_type": "SaveImage", "inputs": { "images": ["8", 0], "filename_prefix": "flux_srpo" }}
}

Complete Workflow: Flux 2 Klein 9B (Distilled, 4-Step)

{
  "1": { "class_type": "UNETLoader", "inputs": { "unet_name": "bigLove_klein1.safetensors", "weight_dtype": "default" }},
  "2": { "class_type": "CLIPLoader", "inputs": { "clip_name": "qwen_3_8b_fp8mixed.safetensors", "type": "flux2" }},
  "3": { "class_type": "VAELoader", "inputs": { "vae_name": "flux2-vae.safetensors" }},
  "4": { "class_type": "CLIPTextEncode", "inputs": { "clip": ["2", 0], "text": "<prompt>" }},
  "5": { "class_type": "ConditioningZeroOut", "inputs": { "conditioning": ["4", 0] }},
  "6": { "class_type": "EmptyFlux2LatentImage", "inputs": { "width": 1024, "height": 1024, "batch_size": 1 }},
  "7": { "class_type": "KSampler", "inputs": {
    "model": ["1", 0],
    "positive": ["4", 0],
    "negative": ["5", 0],
    "latent_image": ["6", 0],
    "seed": 42, "steps": 4, "cfg": 1, "sampler_name": "euler", "scheduler": "simple", "denoise": 1
  }},
  "8": { "class_type": "VAEDecode", "inputs": { "samples": ["7", 0], "vae": ["3", 0] }},
  "9": { "class_type": "SaveImage", "inputs": { "images": ["8", 0], "filename_prefix": "flux_klein" }}
}

Klein note: Uses single CLIPLoader (not DualCLIPLoader) with type: "flux2" and the Qwen3-8B text encoder from text_encoders/. The CLIP loader path resolves from models/text_encoders/.

Two Flux-2-specific gotchas (both fail at the KSampler, not at the loader, so the error points at the wrong node):

• type must be flux2, not flux. Both values exist in the CLIPLoader enum, so flux loads without complaint and then dies during sampling.
• Use EmptyFlux2LatentImage, not EmptyLatentImage — Flux 2 uses a different latent channel count.
• Klein 9B pairs with the Qwen3-8B encoder (qwen_3_8b* from Comfy-Org/vae-text-encorder-for-flux-klein-9b). The similarly-named qwen_3_4b ships in the klein-4b repo and is for the 4B model. Mismatching them raises mat1 and mat2 shapes cannot be multiplied (512x7680 and 12288x4096) — 7680 = 2560x3 (4B hidden size) vs 12288 = 4096x3 (8B) — which reads as a confusing CLIP error rather than a wrong-file error.

Complete Workflow: Flux.1 Dev + Turbo LoRA (4-Step)

{
  "1": { "class_type": "UNETLoader", "inputs": { "unet_name": "flux.1-dev-SRPO-BFL-bf16.safetensors", "weight_dtype": "default" }},
  "2": { "class_type": "LoraLoaderModelOnly", "inputs": { "model": ["1", 0], "lora_name": "flux2-turbo-lora.safetensors", "strength_model": 1.0 }},
  "3": { "class_type": "DualCLIPLoader", "inputs": { "clip_name1": "t5xxl_fp8_e4m3fn.safetensors", "clip_name2": "clip_l.safetensors", "type": "flux" }},
  "4": { "class_type": "VAELoader", "inputs": { "vae_name": "ae.safetensors" }},
  "5": { "class_type": "CLIPTextEncodeFlux", "inputs": {
    "clip": ["3", 0],
    "clip_l": "<short prompt>",
    "t5xxl": "<detailed prompt>",
    "guidance": 3.5
  }},
  "6": { "class_type": "ConditioningZeroOut", "inputs": { "conditioning": ["5", 0] }},
  "7": { "class_type": "EmptyLatentImage", "inputs": { "width": 1024, "height": 1024, "batch_size": 1 }},
  "8": { "class_type": "KSampler", "inputs": {
    "model": ["2", 0],
    "positive": ["5", 0],
    "negative": ["6", 0],
    "latent_image": ["7", 0],
    "seed": 42, "steps": 4, "cfg": 1, "sampler_name": "euler", "scheduler": "simple", "denoise": 1
  }},
  "9": { "class_type": "VAEDecode", "inputs": { "samples": ["8", 0], "vae": ["4", 0] }},
  "10": { "class_type": "SaveImage", "inputs": { "images": ["9", 0], "filename_prefix": "flux_turbo" }}
}

LoRA Support

Custom LoRAs (jellyfish, etc.)

Apply Flux LoRAs with LoraLoaderModelOnly between UNET and KSampler:

{
  "class_type": "LoraLoaderModelOnly",
  "inputs": {
    "model": ["<unet_or_previous_lora>", 0],
    "lora_name": "<lora_file>.safetensors",
    "strength_model": 1.0
  }
}

Klein LoRAs

Klein 9B LoRAs go in loras/Flux.2 Klein 9B/ subfolder:

• klein_slider_detail.safetensors — Detail slider LoRA

VRAM Considerations

• Always clear_vram before switching to Flux from another model family
• T5XXL is the main VRAM consumer alongside the UNET — both stay loaded during sampling
• CLIP-L is small (235MB) and negligible

Tips

1. KSampler CFG must always be 1.0 — all guidance is through CLIPTextEncodeFlux or FluxGuidance
2. SRPO requires BF16 — the FP8 quantization is known to produce broken results with this fine-tune
3. For short prompts (1-2 sentences), increase guidance to 3.5–4.0. For long prompts (paragraph), decrease to 1.0–1.5
4. Flux generates excellent text in images — put text to render in quotes within your prompt
5. Klein 9B is the fastest option at 4 steps — use it for rapid iteration, then switch to SRPO for final quality