MI-World: Multi-Inhabitant World Models with 3D Evolution

Interactive world models simulate future environments in response to user actions. Current approaches rely primarily on video generation, where visual impacts often appear correct while the underlying physical state remains unchanged. This disconnect becomes disruptive when multiple characters share the scene. A removed block can reappear once a camera turns away, character health can remain static despite visible hits, and off-screen non-player characters leave no lasting traces for players who arrive later. We present **MI-World**, an interactive world model that couples multi-character simulation with an evolving 3D voxel map and structured entity records. Scene completion synthesizes unobserved terrain without overwriting established coordinates, preserving earlier structures during exploration. Player and NPC controls update voxel occupancy and character attributes through a shared transition model, enabling autonomous NPCs to modify the environment even while outside any active viewpoint. Perspective video streams are then rendered directly from the updated canonical state. We collect a dataset of 45,572 synchronized multi-character trajectories annotated with explicit interaction events. MI-World achieves a cross-view consistency FVD of 240.7, compared with 280.0 for γ-World and 443.1 for Solaris. Under recorded controls, it recovers reference block edits and attacks at F1 scores of 0.886 and 0.851, respectively. The demo is at [http://miworld-anonymous.github.io/](http://miworld-anonymous.github.io/).