MLLM-4D

MLLM-4D: Towards Visual-based Spatial-Temporal Intelligence

MLLM-4D is a comprehensive framework designed to bridge the gaps in training data curation and model post-training for spatiotemporal understanding and reasoning. It enables multimodal large language models (MLLMs) to perceive and reason about the evolution of 3D space over time from purely visual inputs.

• Paper: MLLM-4D: Towards Visual-based Spatial-Temporal Intelligence
• Repository: https://github.com/GVCLab/MLLM-4D
• Project Page: https://github.com/GVCLab/MLLM-4D

Model Description

MLLM-4D achieves state-of-the-art spatiotemporal intelligence by focusing on the relationships between objects and the camera within 3D space. The model establishes foundational 4D understanding via Supervised Fine-Tuning (SFT) and further catalyzes 4D reasoning capabilities by employing Group Relative Policy Optimization (GRPO) with specialized Spatiotemporal Chain of Thought (ST-CoT) prompting. It achieves these capabilities using purely 2D RGB inputs without architectural modifications.

Usage

To run the inference demo for MLLM-4D, please refer to the setup instructions in the official repository and use the following commands:

# for MLLM-4D-SFT
python scripts/inference.py --model_type "MLLM-4D-SFT" --model_path PATH-to-MLLM-4D-SFT

# for MLLM-4D-RFT
python scripts/inference.py --model_type "MLLM-4D-RFT" --model_path PATH-to-MLLM-4D-RFT

Citation

If you find the work useful, please consider citing:

@article{yin2026mllm4d,
    title={MLLM-4D: Towards Visual-based Spatial-Temporal Intelligence},
    author={Yin, Xingyilang and Li, Chengzhengxu and Chang, Jiahao and Pun, Chi-Man and Cun, Xiaodong},
    journal={arXiv preprint arXiv:2603.00515},
    year={2026}
}