  Understanding how the 3D scene evolves is vital for making decisions in
autonomous driving. Most existing methods achieve this by predicting the
movements of object boxes, which cannot capture more fine-grained scene
information. In this paper, we explore a new framework of learning a world
model, OccWorld, in the 3D Occupancy space to simultaneously predict the
movement of the ego car and the evolution of the surrounding scenes. We propose
to learn a world model based on 3D occupancy rather than 3D bounding boxes and
segmentation maps for three reasons: 1) expressiveness. 3D occupancy can
describe the more fine-grained 3D structure of the scene; 2) efficiency. 3D
occupancy is more economical to obtain (e.g., from sparse LiDAR points). 3)
versatility. 3D occupancy can adapt to both vision and LiDAR. To facilitate the
modeling of the world evolution, we learn a reconstruction-based scene
tokenizer on the 3D occupancy to obtain discrete scene tokens to describe the
surrounding scenes. We then adopt a GPT-like spatial-temporal generative
transformer to generate subsequent scene and ego tokens to decode the future
occupancy and ego trajectory. Extensive experiments on the widely used nuScenes
benchmark demonstrate the ability of OccWorld to effectively model the
evolution of the driving scenes. OccWorld also produces competitive planning
results without using instance and map supervision. Code:
https://github.com/wzzheng/OccWorld.
