Nexus-Gen: A Unified Model for Image Understanding, Generation, and Editing

       

News

• May 27, 2025: We fine-tuned Nexus-Gen using the BLIP-3o-60k dataset, significantly improving the model's robustness to text prompts in image generation, achieving a GenEval score of 0.79. The model checkpoints have been updated.

What is Nexus-Gen

Nexus-Gen is a unified model that synergizes the language reasoning capabilities of LLMs with the image synthesis power of diffusion models. To align the embedding space of the LLM and diffusion model, we conduct a dual-phase alignment training process. (1) The autoregressive LLM learns to predict image embeddings conditioned on multimodal inputs, while (2) the vision decoder is trained to reconstruct high-fidelity images from these embeddings. During training the LLM, we identified a critical discrepancy between the autoregressive paradigm's training and inference phases, where error accumulation in continuous embedding space severely degrades generation quality. To avoid this issue, we introduce a prefilled autoregression strategy that prefills input sequence with position-embedded special tokens instead of continuous embeddings. Through dual-phase training, Nexus-Gen has developed the integrated capability to comprehensively address the image understanding, generation and editing tasks as follows.

Getting Started

Installation

1. Install DiffSynth-Studio from source:

git clone https://github.com/modelscope/DiffSynth-Studio.git
cd DiffSynth-Studio
pip install -e .

2. Install requirements

pip install -r requirements.txt

3. Install ms-swift if you want to perform finetuning on Nexus-Gen.

pip install ms-swift -U

Prepare models

python download_models.py

Image Understanding

python image_understanding.py

Image Generation

Image generation with detailed prompt. (Needs at least 37 GB VRAM)

python image_generation.py

Polish prompt and generate images with Nexus-Gen.

image_generation_with_selfpolish.py

Image generation with less VRAM by cpu offload. (Needs at least 24 GB VRAM)

python image_generation_offload.py

Image Editing

python image_editing.py

Gradio demo

python app.py

Training Codes

Nexus-Gen is trained base on ms-swift and DiffSynth-Studio. You can find the training scripts in train/scripts/train_decoder.sh and train_llm.sh.

Citation

@article{zhang2025nexus-gen,
      title={Nexus-Gen: A Unified Model for Image Understanding, Generation, and Editing}, 
      author={Hong Zhang and Zhongjie Duan and Xingjun Wang and Yingda Chen and Yuze Zhao and Yu Zhang},
      journal={arXiv preprint arXiv:2504.21356},
      year={2025}
}