Initial report: https://youtrack.jetbrains.com/issue/KT-64365/NoClassDefFound-on-upgrading-ksp-to-2.0.0-beta1 I think the issue is caused by adding kotlin-compiler-common-for-ide [without transitive dependencies](https://github.com/google/ksp/blob/88283988491b32a5952f480f031cbeb85893b3c3/kotlin-analysis-api/build.gradle.kts#L59). `io.javaslang:javaslang:2.0.6` should be provided.