This tutorial series has covered various aspects of building a React + GraphQL app with great UX using Apollo, including the basics of GraphQL mutations, server-side rendering, and subscriptions. In part 4 of this series, we're focusing on speeding up GraphQL mutations with optimistic UI and store updates. By utilizing these techniques, developers can hide network latency from their users, providing a better user experience. The tutorial demonstrates how to use Apollo Client's `update` property to perform store updates after a mutation and how to simulate zero-latency server responses using Optimistic UI. With these changes, the addChannel mutation should now look much better, and the app will provide a more seamless user experience.