We've transitioned to GraphQL for our APIs at Courier, driven by its developer-friendly approach and advantages over REST, such as reducing the need for API consumers to know how data is structured, enabling complex sequences of operations, and facilitating versioning, caching, and partial updates. We initially considered AppSync from AWS but ultimately chose Apollo GraphQL due to its simplicity, popularity, and growing community support, which will enable us to implement Apollo Federation and scale our Graph without impacting performance. Our transition has already started with internal APIs and new features, and we're working towards exposing a public GraphQL interface for customers in the future.