ScaleCUA is a framework for scaling open-source computer use agents (CUAs) that autonomously operate graphical user interfaces across multiple platforms including Windows, macOS, Ubuntu, and Android. It provides a large-scale dataset spanning 6 operating systems and 3 task domains, created via a closed-loop pipeline combining automated agents with human experts. The trained agents achieve state-of-the-art results on GUI benchmarks including MMBench-GUI (94.4%), OSWorld-G (60.6%), and WebArena-Lite-v2 (47.4%).