This talk is a guide to developing core UI components that goes beyond coding using TransformingLazyColumn, which is a core scrolling component for the round screens of Wear OS, as an example. We'll discuss the critical decisions behind building an API. We’ll cover how to distinguish between core, unique functionality and volatile, specific behaviors, and evolve the API strategically. We'll explore why measuring is more crucial than assuming when it comes to performance optimizations. We’ll touch upon balancing parallel development and client migration, and the importance of empowering other teams by giving them control over their own migration process.