Why you care: You can run experiments either on a thin client, such as a web browser, or on a thick client, such as a native mobile app or a desktop client app. Changes for a webpage, regardless of whether it is frontend or backend, are fully controlled by the server. This is very different from a thick client. With an explosive growth of mobile usage, the number of experiments running on mobile apps has also grown (Xu and Chen 2016). Understanding the differences between thin and thick clients due to release process, infrastructure, and user behavior is useful to ensure trustworthy experiments.