vllm-omni/docs/user_guide/quantization/overview.md

Quantization

vLLM-Omni exposes quantization through the unified quantization_config path. The same configuration entrypoint is used across diffusion-only models, multi-stage omni/TTS models, and multi-stage diffusion models, but each model type has a different quantization scope.

Quantization Modes

Mode	Guide	Description	Methods
Online quantization	Online Quantization	vLLM-Omni computes quantized weights and scales while loading the model.	FP8 W8A8, Int8 W8A8
Runtime attention quantization	Quantized KV Cache	vLLM-Omni dynamically quantizes eligible diffusion Flash Attention tensors during inference.	FP8 FA
Pre-quantized checkpoints	Method-specific guides	The checkpoint or an offline quantizer provides quantized weights and scales before serving.	ModelOpt, GGUF, AutoRound, msModelSlim, serialized Int8

Hardware Support

Device	FP8 W8A8	Int8 W8A8	ModelOpt	GGUF	AutoRound	msModelSlim
NVIDIA Blackwell GPU (SM 100+)	✅	✅	✅	✅	✅	❌
NVIDIA Ada/Hopper GPU (SM 89+)	✅	✅	✅	✅	✅	❌
NVIDIA Ampere GPU (SM 80+)	✅	✅	⭕	✅	✅	❌
AMD ROCm	⭕	⭕	⭕	⭕	⭕	❌
Intel XPU	⭕	⭕	⭕	⭕	✅	❌
Ascend NPU	❌	✅	❌	❌	❌	✅

Legend: ✅ supported, ❌ unsupported, ⭕ not verified in this guide. FP8 on Ampere may use a weight-only path where available.

Model Type Support

Diffusion Model (Qwen-Image, Wan2.2)

These models run a diffusion transformer as the primary inference module. The default quantization target is the transformer; tokenizer, scheduler, text encoder, and VAE stay on the base checkpoint unless a method guide says otherwise.

Method	Guide	Mode	Example models	Status
FP8 W8A8	FP8	Online W8A8 or checkpoint FP8	Qwen-Image; Wan2.2 is not validated	Validated for Qwen-Image family and other DiT models
Int8 W8A8	Int8	Online or serialized W8A8	Qwen-Image; Wan2.2 is not validated	Validated for Qwen-Image and Z-Image
ModelOpt	ModelOpt	Pre-quantized FP8 checkpoints	Qwen-Image, Z-Image, FLUX.2, HunyuanImage-3.0	Validated for ModelOpt FP8 diffusion checkpoints
GGUF	GGUF	Pre-quantized transformer weights	Qwen-Image	Validated where a model-specific GGUF adapter exists
AutoRound	AutoRound	Pre-quantized W4A16 checkpoints	FLUX.1-dev; Qwen-Image/Wan2.2 not validated	Checkpoint-driven
msModelSlim	msModelSlim	Pre-quantized Ascend checkpoints	Wan2.2 recipe; HunyuanImage-3.0 inference target	Ascend/NPU path

Multi-Stage Omni/TTS Model (Qwen3-Omni, Qwen3-TTS)

These models combine an AR language model with audio, vision, talker, or TTS stages. Quantization is scoped to the AR language-model stage when the checkpoint contains a supported quantization_config; the non-AR stages stay in BF16 unless the model guide explicitly adds support.

Method	Guide	Scope	Example models	Status
ModelOpt	ModelOpt	Thinker or language-model checkpoint config	Qwen3-Omni thinker	ModelOpt checkpoint path
Int8	Int8	Not currently validated for omni/TTS stages	Qwen3-Omni, Qwen3-TTS	Not validated
GGUF	GGUF	Not currently validated for omni/TTS stages	Qwen3-Omni, Qwen3-TTS	Not validated
AutoRound	AutoRound	Thinker or language-model checkpoint config	Qwen2.5-Omni, Qwen3-Omni	Supported through AutoRound checkpoints
msModelSlim	msModelSlim	Not currently validated for omni/TTS stages	Qwen3-Omni, Qwen3-TTS	Not validated

Multi-Stage Diffusion Model (BAGEL, GLM-Image)

These models split generation across multiple stages. Quantization must be attached to the intended stage rather than applied globally.

Method	Guide	Scope	Example models	Status
FP8	FP8	Stage-specific DiT or transformer module	BAGEL, GLM-Image	Requires model-specific validation
Int8	Int8	Stage-specific DiT or transformer module	BAGEL, GLM-Image	Requires model-specific validation
ModelOpt	ModelOpt	Checkpoint-defined diffusion stage	BAGEL, GLM-Image	Requires model-specific validation
GGUF	GGUF	Stage-specific transformer weights	BAGEL, GLM-Image	No validated adapter listed
AutoRound	AutoRound	Checkpoint-defined stage	BAGEL, GLM-Image	No validated checkpoint listed
msModelSlim	msModelSlim	Ascend-generated stage weights	GLM-Image	Requires model-specific adaptation

!!! note "Online quantization" means vLLM-Omni computes the quantization data while loading the model. "Pre-quantized" means the checkpoint or external quantizer provides the required quantized weights and scales.

Quantization Scope

Diffusion Model (Qwen-Image, Wan2.2)

The default target is the diffusion transformer. Component routing is available through build_quant_config():

from vllm_omni.quantization import build_quant_config

config = build_quant_config({
    "transformer": {"method": "fp8"},
    "vae": None,
})

Component	Default quantized?	Notes
Diffusion transformer	Yes	Primary target for FP8, Int8, ModelOpt, GGUF, AutoRound, and msModelSlim
Text encoder	No	Keep BF16 unless a method-specific guide documents support
VAE	No	Keep BF16; storage-only paths are method-specific
Scheduler/tokenizer	No	Loaded from the base model repository

Multi-Stage Omni/TTS Model (Qwen3-Omni, Qwen3-TTS)

Component	Default quantized?	Notes
Thinker or AR language model	Yes, when checkpoint config is supported	ModelOpt FP8/NVFP4 or AutoRound checkpoint config
Audio encoder	No	BF16
Vision encoder	No	BF16
Talker or TTS stage	No	BF16 unless model-specific support is documented
Code2Wav	No	BF16

Multi-Stage Diffusion Model (BAGEL, GLM-Image)

Component	Default quantized?	Notes
Selected diffusion or transformer stage	Method-specific	Must be routed to the intended stage
Other generation stages	No	Keep BF16 unless separately validated
VAE, tokenizer, scheduler	No	Loaded from the base checkpoint

Python API

build_quant_config() accepts strings, dictionaries, per-component dictionaries, existing QuantizationConfig objects, or None.

from vllm_omni.quantization import build_quant_config

build_quant_config("fp8")
build_quant_config({"method": "fp8", "activation_scheme": "static"})
build_quant_config("auto-round", bits=4, group_size=128)
build_quant_config({"method": "gguf", "gguf_model": "/path/to/model.gguf"})
build_quant_config({"transformer": {"method": "fp8"}, "vae": None})
build_quant_config(None)