jankin123/4DThinker-3B

4DThinker: Thinking with 4D Imagery for Dynamic Spatial Understanding

Paper | Code

4DThinker is a framework that enables Vision-Language Models (VLMs) to "think with 4D" through dynamic latent mental imagery—internally simulating how scenes evolve within the continuous hidden space. It addresses dynamic spatial reasoning from monocular video by grounding the model in dynamic visual semantics.

This repository contains the trained model checkpoints from Qwen2.5-VL-3B for 4DThinker.

Model Structure

model/
├── dift/
│   ├── checkpoints/          # DIFT-stage model weights
│   │   ├── model-00001-of-00002.safetensors
│   │   ├── model-00002-of-00002.safetensors
│   │   ├── config.json
│   │   ├── tokenizer.json
│   │   └── ...
│   └── tensorboard/          # DIFT training logs
└── 4drl/
    ├── model-00001-of-00002.safetensors
    ├── model-00002-of-00002.safetensors
    ├── config.json
    ├── tokenizer.json
    ├── trainer_state.json
    └── ...

Models

Model	Stage	Base Model	Description
dift/checkpoints/	DIFT	Qwen2.5-VL-3B-Instruct	Supervised with cosine similarity loss on latent visual tokens
4drl/	4DRL (GRPO)	DIFT checkpoint	Reinforced with answer-based rewards

Special Tokens

Three special tokens are added to the Qwen2.5-VL vocabulary to support latent imagery:

Token	Description
`<	latent_pad
`<	latent_start
`<	latent_end

Usage

from transformers import Qwen2_5_VLForConditionalGeneration, AutoProcessor

model = Qwen2_5_VLForConditionalGeneration.from_pretrained(
    "jankin123/4DThinker-3B",
    subfolder="4drl",
    torch_dtype="auto",
    device_map="auto"
)
processor = AutoProcessor.from_pretrained("jankin123/4DThinker-3B", subfolder="4drl")

Citation

@article{4dthinker,
  title={4DThinker: Thinking with 4D Imagery for Dynamic Spatial Understanding},
  author={Zhang, Quanchen and others},
  journal={arXiv preprint arXiv:2605.05997},
  year={2026}
}

Bibtex

If you find 4DThinker helpful for your work, please cite

@article{chen20264dthinker,
  title={4DThinker: Thinking with 4D Imagery for Dynamic Spatial Understanding},
  author={Chen, Zhangquan and Zhang, Manyuan and Yu, Xinlei and An, Xiang and Li, Bo and Xie, Xin and Wang, ZiDong and Sun, Mingze and Chen, Shuang and Li, Hongyu and others},
  journal={arXiv preprint arXiv:2605.05997},
  year={2026}
}

License

Apache License 2.0