In order to target on-device AI with diverse hardware, critical power requirements, and realtime processing needs, a single monolithic solution is not practical. Instead, a modular, layered, and extendable architecture is desired. ExecuTorch defines a streamlined workflow to prepare (export, transformation, and compilation) and execute a PyTorch program, with opinionated out-of-the-box default components and well-defined entry points for customizations. This architecture greatly improves portability, allowing engineers to use a performant lightweight, cross-platform runtime that easily integrates into different devices and platforms.