The article outlines the process of migrating Android applications from the PubNub SDK v3 to v4, highlighting improvements in the latter that enhance code readability and functionality. The v4 SDK introduces a Fluent API, which simplifies initialization and configuration, and separates the configuration from instantiation, making the code more understandable and self-documenting. It also streamlines the handling of publish/subscribe operations and introduces a more efficient approach to managing callbacks and presence events by offering strongly typed events with additional context. The migration guide includes practical examples, sample applications, and code comparisons between v3 and v4 to assist developers in transitioning their projects smoothly. Additionally, it touches on the benefits of using v4 for multiplexing and channel groups, providing a more Java-friendly approach, and hints at future articles that will cover advanced topics such as mobile push notifications, history, and access management.