This is a quantized version of Qwen-Image-2512 for the vLLM-Omni backend with optimized Humming kernels, the fastest way we ship this model. Quantization was produced with ByteShape's ShapeLearn, which learns the optimal datatype per tensor to maintain high quality even at very low bitlengths.

Experimental. We tested this flow with vLLM 0.24.0, vLLM-Omni 0.24.0, vllm-omni-humming 0.3.0, and humming-kernels 0.1.11 on NVIDIA 30-, 40-, and 50-series and RTX Pro 6000 GPUs. Linux and NVIDIA only (SM75+, driver ≥ 575).

Six sizes are available, from 17.29 GB (6.77 bpw) down to 7.83 GB (3.07 bpw). All variants generate high-quality images.

Each package bundles the text encoder, VAE, scheduler, and tokenizer, so there are no separate component downloads: you pick a size and serve.

Prefer ComfyUI or a wider hardware range? We also publish GGUF builds of the same model for ComfyUI and stable-diffusion.cpp: byteshape/Qwen-Image-2512-GGUF.

To learn more about ShapeLearn, and for the full walkthrough with screenshots and a downloadable ComfyUI workflow, visit our blog.

If you have questions or want to share feedback, reach us on Reddit.

A Note on Speed

Unlike the decoding stage of an LLM, diffusion inference is not heavily constrained by memory bandwidth. Compressing the model therefore does not necessarily make image generation faster. Quantization here buys you VRAM headroom, not throughput. Backend optimization is what moves the needle.

This backend uses optimized Humming kernels and is roughly 2-3x faster than the GGUF path. On an RTX 5090 each step takes around 0.5 seconds, so a 20-step image samples in about 10 seconds.

Backend	Time per step (RTX 5090)	Time for 20 steps
vLLM-Omni (this repo)	~0.5 s	~10 s
GGUF	~1.2 s	~24 s

For measured peak VRAM and end-to-end times for every size at four output resolutions, with and without CPU offload, see the VRAM and speed table in the blog post.

What Do the Sizes Look Like?

One prompt rendered by BF16 and all six Humming sizes, with a matching close-up crop of the ring face under each variant

Quality does not fall off a cliff as the bits come off. BF16, 6.77 and 5.33 bpw are near-interchangeable on this prompt, down to the same scratch fan and specular streak; from 4.70 bpw a soft grey haze spreads across the ring face and the surviving scratches grow thicker and fewer at each step, and at 3.07 bpw the composition itself drifts, with a narrower band sitting higher in the frame; even there the image is still a clean macro shot. Differences like these are subtle and highly prompt-dependent, and the row above is one prompt out of 24.

Judge for yourself: the blog post walks through the full set, and the interactive comparison explorer lets you A/B any two variants across 24 curated prompts at full resolution, with a slider, zoom, and a curator note for each prompt. If you read the outputs differently, tell us on Reddit.

Repository Layout

The package is a shared shell (the pipeline) plus a pool of transformers, one per size:

Qwen-Image-2512/          # the shell: text encoder, VAE, scheduler, tokenizer
quantized_models/
  6.77bpw/transformer/
  5.33bpw/transformer/
  4.70bpw/transformer/
  4.18bpw/transformer/
  3.57bpw/transformer/
  3.07bpw/transformer/

You download the shell once, then drop the transformer of your choice into it.

Available Models

Model ID	Bits/Weight	Transformer Size	Folder
VLLM-1	3.07	7.83 GB	`quantized_models/3.07bpw`
VLLM-2	3.57	9.11 GB	`quantized_models/3.57bpw`
VLLM-3	4.18	10.68 GB	`quantized_models/4.18bpw`
VLLM-4	4.70	12.00 GB	`quantized_models/4.70bpw`
VLLM-5	5.33	13.60 GB	`quantized_models/5.33bpw`
VLLM-6	6.77	17.29 GB	`quantized_models/6.77bpw`

On VRAM. The size above is the diffusion transformer only. The shell adds a BF16 text encoder (~16.6 GB) and the VAE (~0.25 GB), so keeping everything resident on the GPU needs roughly transformer + 17 GB: about 25 GB for the smallest size and 34 GB for the largest.

≤ 32 GB cards (including the RTX 5090): serve with --enable-cpu-offload. All six sizes work; the text encoder lives in system RAM.
48 GB and larger (e.g. RTX Pro 6000): drop --enable-cpu-offload for full speed.

Selection rule: take the largest model that comfortably fits your card. Since compression does not speed up diffusion, there is little reason to go smaller than your VRAM allows.

Quick Start

1. Set up the environment

bash

conda create -y -n qwen-image-humming python=3.12
conda activate qwen-image-humming

# torch trio (cu129)
pip install torch==2.11.0 torchvision==0.26.0 torchaudio==2.11.0 \
  --index-url https://download.pytorch.org/whl/cu129

# vLLM 0.24.0 (cu129 wheel)
printf 'torch==2.11.0+cu129\ntorchvision==0.26.0+cu129\ntorchaudio==2.11.0+cu129\n' > constraints.txt
PIP_CONSTRAINT=constraints.txt pip install \
  https://github.com/vllm-project/vllm/releases/download/v0.24.0/vllm-0.24.0+cu129-cp38-abi3-manylinux_2_28_x86_64.whl

# vLLM-Omni + our loader plugin
PIP_CONSTRAINT=constraints.txt pip install vllm-omni==0.24.0
PIP_CONSTRAINT=constraints.txt pip install vllm-omni-humming==0.3.0

# humming kernels: must be >= 0.1.11 (older versions produce corrupted images)
pip install --no-deps "humming-kernels>=0.1.11"

vllm-omni-humming is our own plugin, and it is the one required extra piece for this path: stock vLLM-Omni cannot read a pre-quantized Humming checkpoint on its own. The plugin registers itself and detects our models from their transformer/config.json.

2. Download the model

Grab the shell and the size you want:

bash

pip install -U huggingface_hub

# the shell + one transformer (here the 3.07 bpw size)
hf download byteshape/Qwen-Image-2512-Humming \
  --include "Qwen-Image-2512/*" --include "quantized_models/3.07bpw/*" \
  --local-dir Qwen-Image-2512-Humming
cd Qwen-Image-2512-Humming

Then drop your chosen transformer into the shell. The folder is already named transformer, so it lands with the correct name:

bash

# symlink it in (instant, no extra disk) ...
ln -sfn ../quantized_models/3.07bpw/transformer Qwen-Image-2512/transformer

# ... or move it in (a real, self-contained model dir)
mv quantized_models/3.07bpw/transformer Qwen-Image-2512/transformer

To try a different size later, swap the symlink, or move one transformer out and another in. The folders are named by bit-width (6.77bpw, 4.18bpw, 3.07bpw, and so on).

3. Serve

From the folder root:

bash

vllm-omni serve Qwen-Image-2512 \
  --omni --served-model-name Qwen/Qwen-Image-2512 \
  --enable-cpu-offload --port 8124

Keep --enable-cpu-offload on cards with ≤ 32 GB (an RTX 5090 needs it); drop it on larger GPUs for full speed.

Do not pass --diffusion-quantization-config or set any VLLM_HUMMING_* variables. The plugin drives everything from the checkpoint.

The first serve on a new GPU spends a few minutes compiling kernels for your card, then caches them.

4. Generate

The server exposes the OpenAI images API:

bash

curl -s http://127.0.0.1:8124/v1/images/generations \
  -H "Content-Type: application/json" \
  -d '{
    "model": "Qwen/Qwen-Image-2512",
    "prompt": "A red panda on a mossy log at dawn",
    "size": "1024x1024",
    "num_inference_steps": 20,
    "true_cfg_scale": 2.5,
    "negative_prompt": " ",
    "seed": 1234
  }' \
  | python3 -c "import sys,json,base64; d=json.load(sys.stdin); open('out.png','wb').write(base64.b64decode(d['data'][0]['b64_json']))"

Always include a negative_prompt, even a single space. vLLM-Omni applies classifier-free guidance only when a negative prompt is present with true_cfg_scale > 1; with none, guidance is skipped and the image comes out flatter and lower-contrast.

Driving the Server from ComfyUI

If you prefer a GUI over curl, the ComfyUI-vLLM-Omni custom node sends generation requests to a running vLLM-Omni server, local or remote. ComfyUI is only the front end; vLLM still does the work.

Install the node into your ComfyUI installation:

bash

cd /path/to/ComfyUI/custom_nodes
git clone https://github.com/vllm-project/vllm-omni.git
cp -r vllm-omni/apps/ComfyUI-vLLM-Omni ComfyUI-vLLM-Omni
rm -rf vllm-omni

Restart ComfyUI (python main.py), then open a browser and go to http://127.0.0.1:8188 to reach the ComfyUI interface. A new vLLM-Omni folder appears in the Node Library sidebar. No extra Python packages are needed beyond ComfyUI's own.

Keep the vLLM-Omni server from step 3 running. ComfyUI reaches it at http://127.0.0.1:8124/v1. If ComfyUI runs on a different machine, use the server's address instead of 127.0.0.1.

For the workflow, download qwen-image-humming-vllm-omni.json from our blog post and load it with Ctrl+O, or start from ComfyUI's built-in template at sidebar → Templates → vLLM-Omni → vLLM-Omni Image Generation.

In the Generate Image node, set:

url → http://127.0.0.1:8124/v1
model → Qwen/Qwen-Image-2512
prompt / negative_prompt → your text (negative: at least a space)
width / height → e.g. 1024 x 1024

In the attached Diffusion Sampling Params node, set the seed, num_inference_steps (e.g. 20), and true_cfg_scale (e.g. 2.5), then run the workflow.

Troubleshooting

Symptom	Cause and fix
`HummingConfig ... unexpected keyword argument`, or a shape mismatch on `img_mod.1` / `txt_mod.1` at load	The plugin is not installed in the active environment. Check with `pip show vllm-omni-humming`.
Grainy or speckled images	The Humming kernels are too old. Reinstall with `pip install --no-deps "humming-kernels>=0.1.11"`.
Flat, low-contrast images	No `negative_prompt` was sent, so CFG was skipped. Pass one; a single space is enough.
Out of memory on serve	Add `--enable-cpu-offload`, or pick a smaller bit-width from the table above.