Runway releases Gen-4.5 video generation model with improved physics simulation

Runway/Gen-4.5

Runway released Gen-4.5 in December 2025, a video generation model that excels at rendering physical phenomena such as momentum and fluid dynamics. At launch, it ranked at the top of AI video generators, outperforming competitors at realistic physics simulation. However, objects sometimes disappear and reappear across frames, and effects occasionally appear before their causes.

• Ranked at top of AI video generators at launch
• Excels at rendering momentum, fluid dynamics and object interactions
• Improved over Gen-3 in physical realism and consistency
• Limitations include occasional object pop-in/pop-out and temporal inconsistencies in rare scenarios