Modifications: the original weights were quantized (e.g. W4A4 / FP4 / INT4 / FP8) and repackaged for the QuantFunc inference engine — a "modification" under Apache-2.0 §4(b).
Upstream license: the base model is licensed under the Apache License 2.0, included here as LICENSE-APACHE; the upstream copyright and attribution notices are retained.
This derivative: the QuantFunc quantization & packaging are additionally provided under the QuantFunc Model License (see LICENSE).
This repository is not affiliated with or endorsed by the upstream model authors.

Disclaimer: Derived from FLUX.2 [klein] by Black Forest Labs. This is not an official Black Forest Labs product and is not endorsed by or affiliated with BFL. "FLUX" is a trademark of Black Forest Labs.

QuantFunc

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⚡ FLUX.2 Klein 4B — pre-quantized for speed. The lighter, fast Klein variant for text-to-image and reference-based editing, running 2x–11x faster with the QuantFunc plugin.

This series ships the distilled (4-step) and base (28-step) FLUX.2 Klein 4B transformers across three GPU tiers — 50x FP4 (Blackwell), 40x INT4+FP8 (Ada/Hopper), 30x-below INT4+INT8 (RTX 30 and below) — so every card gets the fastest path it can run.

Powered by the QuantFunc ComfyUI plugin — the fastest diffusion inference engine:

🚀 2x–11x speedup over standard BF16/FP16 Python pipelines (pre-exported → even faster loading).
⚙️ Native C++/CUDA (libquantfunc.so / quantfunc.dll) with zero Python model dependencies.
🧩 Dual engine (SVDQ offline + Lighting runtime 4-bit), zero-cost LoRA stacking, reference-image editing & inpainting.
🟢 Full GPU coverage — RTX 20/30/40/50 · A100/H100/H200/B100/B200/GB300 · RTX 6000 Ada / PRO Blackwell (CUDA 12 & 13); native FP4 on Blackwell.

👉 Install the plugin: https://github.com/RealJonathanYip/ComfyUI-QuantFunc

Klein-4B-Series

Pre-quantized FLUX.2 Klein 4B model series by QuantFunc, Lighting backend. Text-to-image and reference-based image editing.

✨ Both the distilled AND the non-distilled (base) model are supported, and the series ships three GPU tiers so every card gets the best path it can run: 50x (Blackwell, FP4) · 40x (RTX 40 / Ada & Hopper, INT4 + FP8) · 30x-below (RTX 30 and below, INT4 + INT8).

Overview

FLUX.2 Klein is Black Forest Labs' Flux.2 family. The 4B variant (the lighter, fast variant, transformer K=3072). QuantFunc ships, pre-quantized:

Distilled transformer — 4-step, fastest few-step generation/editing.
Base / non-distilled transformer — the full 28-step model with classical CFG (--guidance-scale 4.0), highest quality.

…each in 3 hardware tiers (below). Distilled and base share the same base-model — only the transformer file differs.

Hardware tiers (pick by GPU)

FP4 needs Blackwell (SM120); FP8 needs Ada (SM89) or Hopper (SM90) — e.g. RTX 40 / L40 / H100 / H200; INT4/INT8 run everywhere (Ampere/Turing, e.g. RTX 30/20, A100). So:

Tier	GPUs	attention + FFN	modulation/embedders/head	base-model
`50x`	Blackwell (SM120+) — RTX 50 series, B100/B200/GB200, RTX PRO Blackwell	FP4	FP8	`klein-4b-series-50x-above-base-model` (FP4 text encoder)
`40x`	RTX 40 / Ada (SM89) & Hopper (SM90) — RTX 40 series, L40/L40S, H100, H200	INT4	FP8	`klein-4b-series-50x-below-base-model` (INT4 text encoder)
`30x-below`	RTX 30 and below (pre-FP8) — RTX 30/20, A100, A40, T4, down to RTX 2080	INT4	INT8	`klein-4b-series-50x-below-base-model` (INT4 text encoder)

40x and 30x-below share the same INT4 base-model — they differ only in the transformer's 8-bit precision (FP8 vs INT8). 50x uses the FP4 base-model.

Directory Structure

Klein-4B-Series/
├── klein-4b-series-50x-above-base-model/         # FP4 text encoder + VAE(enc+dec) + tokenizer + scheduler   (50x)
├── klein-4b-series-50x-below-base-model/   # INT4 text encoder + VAE(enc+dec) + tokenizer + scheduler  (40x & 30x-below)
├── transformer/
│   ├── config.json
│   ├── klein-4b-50x-lighting.safetensors             # distilled, FP4   (50x)
│   ├── klein-4b-base-50x-lighting.safetensors        # base 28-step, FP4 (50x)
│   ├── klein-4b-40x-lighting.safetensors             # distilled, INT4 + FP8  (40x)
│   ├── klein-4b-base-40x-lighting.safetensors        # base 28-step, INT4 + FP8(40x)
│   ├── klein-4b-30x-below-lighting.safetensors       # distilled, INT4 + INT8 (30x-below)
│   └── klein-4b-base-30x-below-lighting.safetensors  # base 28-step, INT4 + INT8(30x-below)
└── precision-config/
    ├── 50x-fp4-f8-sample.json
    ├── 40x-int4-f8-sample.json
    └── 30x-below-int4-i8-sample.json

Status: ✓ All weights uploaded; the VAE includes both encoder and decoder. Every tier × {distilled, base} is visually validated to generate correctly.

Distilled (4-step) vs Base (28-step)

Transformer	Source	Steps	Guidance	Best for
`klein-4b-<tier>-lighting.safetensors`	Klein distilled	4	none (guidance-distilled)	Fastest
`klein-4b-base-<tier>-lighting.safetensors`	Klein base	28	`--guidance-scale 4.0` (classical CFG)	Highest quality

Inference

bash

# 50x — Blackwell (RTX 50 / B-series). Distilled, 4-step:
quantfunc --model-dir klein-4b-series-50x-above-base-model \
  --transformer transformer/klein-4b-50x-lighting.safetensors \
  --model-backend lighting --auto-optimize --steps 4 \
  --prompt "a cute cat on a windowsill, watercolor style" --output out.png

# 40x — RTX 40 / Ada or Hopper (H100/H200). Base 28-step (classical CFG):
quantfunc --model-dir klein-4b-series-50x-below-base-model \
  --transformer transformer/klein-4b-base-40x-lighting.safetensors \
  --model-backend lighting --auto-optimize --steps 28 --guidance-scale 4.0 \
  --prompt "a cute cat on a windowsill, watercolor style" --output out.png

# 30x-below — RTX 30 and below. Distilled, 4-step:
quantfunc --model-dir klein-4b-series-50x-below-base-model \
  --transformer transformer/klein-4b-30x-below-lighting.safetensors \
  --model-backend lighting --auto-optimize --steps 4 \
  --prompt "a cute cat on a windowsill, watercolor style" --output out.png

--auto-optimize picks the VRAM/attention/compression strategy for your GPU. The ComfyUI Lighting plugin auto-selects the matching tier + precision-config.

Precision Config (precision-config/)

File	Tier / GPU	attention+FFN	islands
`50x-fp4-f8-sample.json`	50x — Blackwell (SM120+)	FP4	FP8
`40x-int4-f8-sample.json`	40x — Ada (SM89) & Hopper (SM90): RTX 40, L40, H100, H200	INT4	FP8
`30x-below-int4-i8-sample.json`	30x-below — RTX 30/20, A100 (pre-FP8)	INT4	INT8

These per-layer configs control the Lighting backend's quantization precision — customize for your own speed/quality trade-off.

Related Repositories

QuantFunc/Klein-9B-Series — FLUX.2 Klein 9B
QuantFunc/Qwen-Image-Series · QuantFunc/Qwen-Image-Edit-Series · QuantFunc/Z-Image-Series

License

The pre-quantized weights are derived from FLUX.2 Klein. Users must comply with the original Black Forest Labs FLUX.2 license. The QuantFunc inference engine and plugins are licensed separately.

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QuantFunc/Klein-4B-Series

License & Attribution