September 2025 monthly summary for JetBrains/intellij-community focusing on feature deprecation and test stability related to Kotlin language version management. Key changes center on dropping Kotlin 1.9 support in preparation for the long-term deprecation roadmap, with minimal disruption to existing functionality.

May 2025 monthly summary for google/kotlin focusing on performance optimization in the K2 compiler's FIR processing. Implemented a targeted refactor to improve performance by using unordered hash maps in scope and resolution components. This work aligns with goals to reduce compilation time and improve scalability for Kotlin projects.

Month: 2025-04 — Focused on reducing technical debt and simplifying the Kotlin compiler surface for Kotlin 1.8+. Delivered a cleanup of obsolete diagnostics, checkers, and build flags, removing noise and helping downstream users by streamlining maintenance and future-proofing the compiler as Kotlin 1.8+ stabilizes. Key deliverables include a targeted cleanup of 1.8+ related diagnostics and checkers, removal of the -Xenable-builder-inference flag, and pruning related test data. The work encompassed 7 commits that remove unused or deprecated components and flags across the repo.