Act-One is an innovative tool launched by Runway Research that generates expressive character performances from simple video input. This tool represents a significant advancement in using generative models for rich, human-like motion and animated content. The breakthrough of Act-One lies in its ability to convert an actor's performance into a 3D model suitable for animation pipelines while retaining emotional depth and detail. Unlike traditional facial animation processes, Act-One's workflow is entirely driven by the actor's performance, requiring no additional equipment. The advent of Act-One opens up new possibilities for creative character design and animation, accurately translating performances to characters of different proportions while maintaining high-fidelity facial animations from various camera angles. Additionally, Act-One is committed to responsible development and deployment, including content review and safety measures.