Z-Image-Turbo — MLX (2-bit Quantized)

MLX conversion of Tongyi-MAI/Z-Image-Turbo for Apple Silicon.

This is the 2-bit quantized MLX conversion. Linear layer weights are quantized to 2-bit with group_size=64. VAE remains in float16 to preserve image quality. Note: 2-bit quantization may result in noticeable quality degradation.

Model size: 4.04 GB

All Available MLX Variants

Variant	Size	Quantization	Link
Full Precision (fp16)	20.54 GB	None	andrevp/Z-Image-Turbo-MLX
8-bit	11.37 GB	8-bit, group_size=64	andrevp/Z-Image-Turbo-MLX-8bit
4-bit	6.48 GB	4-bit, group_size=64	andrevp/Z-Image-Turbo-MLX-4bit
2-bit	4.04 GB	2-bit, group_size=64	andrevp/Z-Image-Turbo-MLX-2bit

About Z-Image-Turbo

Z-Image is an efficient 6B-parameter image generation foundation model using a Scalable Single-Stream Diffusion Transformer (S3-DiT) architecture. Z-Image-Turbo is the distilled variant with only 8 NFEs (Number of Function Evaluations), achieving sub-second inference latency.

Key Features

Photorealistic image generation with state-of-the-art quality
Bilingual text rendering (English & Chinese)
Strong instruction adherence
8-step inference — distilled via Decoupled-DMD + Reinforcement Learning (DMDR)
No CFG required — guidance_scale=0.0

Architecture

Component	Architecture	Parameters
Text Encoder	Qwen3 (36 layers, hidden_size=2560, GQA with 32/8 heads)	~7.8 GB (fp16)
Transformer	ZImageTransformer2DModel (30 layers, dim=3840, 30 heads)	~12.3 GB (fp16)
VAE	AutoencoderKL (from Flux, 16 latent channels)	~160 MB (fp16)
Tokenizer	Qwen2Tokenizer (vocab_size=151,936)	—
Scheduler	FlowMatchEulerDiscreteScheduler	—

The S3-DiT architecture concatenates text tokens, visual semantic tokens, and image VAE tokens at the sequence level as a unified input stream, maximizing parameter efficiency compared to dual-stream approaches.

Quantization Details

Parameter	Value
Bits	2
Group Size	64
Quantized Components	Text Encoder (Qwen3), Transformer (ZImageTransformer2DModel)
Non-Quantized Components	VAE (AutoencoderKL) — kept at float16 for image quality
Quantized Tensors	526 Linear layer weight tensors
Method	MLX group quantization (`mlx.core.quantize`)

Only 2D weight tensors from Linear layers are quantized. Normalization layers, biases, embeddings, and position encodings remain in float16.

Component Sizes

Component	Original (bf16)	This Variant (2-bit Quantized)
Text Encoder	7.8 GB	~1.9 GB
Transformer	24.6 GB	~1.9 GB
VAE	160 MB	160 MB
Total	~32.6 GB	4.04 GB

Original Model

Source: Tongyi-MAI/Z-Image-Turbo
Authors: Tongyi MAI Team (Alibaba)
License: Apache 2.0
Papers:
- Z-Image: arXiv:2511.22699
- Decoupled-DMD: arXiv:2511.22677
- DMDR: arXiv:2511.13649

Original Usage (PyTorch/CUDA)

import torch
from diffusers import ZImagePipeline

pipe = ZImagePipeline.from_pretrained(
    "Tongyi-MAI/Z-Image-Turbo",
    torch_dtype=torch.bfloat16,
)
pipe.to("cuda")

prompt = "Young Chinese woman in red Hanfu, intricate embroidery, ancient temple backdrop"

image = pipe(
    prompt=prompt,
    height=1024,
    width=1024,
    num_inference_steps=9,   # Results in 8 DiT forwards
    guidance_scale=0.0,      # No CFG for Turbo models
    generator=torch.Generator("cuda").manual_seed(42),
).images[0]

image.save("example.png")

Conversion Details

Converted using MLX {0.30.6} on Apple Silicon
Weights converted from bfloat16 to float16
SafeTensors format (MLX-compatible)
All weight keys preserved and verified
VAE kept at float16 across all quantization levels
Verified: no NaN/Inf values, all shapes consistent, all index files valid

Citation

@article{z-image2025,
    title={Z-Image: An Efficient Image Generation Foundation Model with Scalable Single Stream Diffusion Transformer},
    author={Tongyi MAI Team},
    journal={arXiv preprint arXiv:2511.22699},
    year={2025}
}

@article{decoupled-dmd2025,
    title={Decoupled Consistency Model Distillation},
    author={Liu et al.},
    journal={arXiv preprint arXiv:2511.22677},
    year={2025}
}

@article{dmdr2025,
    title={DMDR: Fusing DMD with Reinforcement Learning},
    author={Jiang et al.},
    journal={arXiv preprint arXiv:2511.13649},
    year={2025}
}