The text discusses the transition from using the old K1 compiler in Apollo Kotlin to the new K2 compiler, which is part of Kotlin 2. The migration process involved maintaining a dedicated branch for non-breaking changes and iterating through beta and release candidates until a stable version was reached. The switch has improved build performance, with a noticeable 40% reduction in compilation time on a MacBook Pro with a 10-core M1 Max chip. The new compiler also brings improvements to the Compose compiler's release cycles and version numbers. Although some compatibility issues were encountered, especially with native and JS code, the K2 compiler has been found to have better forward compatibility for Android and JVM projects. The future development of language features such as Guards, Context sensitive resolution, and Explicit backing fields is expected to be easier with the new compiler. Overall, the transition to K2 has brought significant benefits to Apollo Kotlin's build performance and is recommended for other developers to upgrade their own projects.