Alexander Asafo created the Scala 3 Inferred Union Types Warning System for the scala/scala3 repository, introducing a new compiler phase that detects and warns when a type argument is inferred as a union type. Using Scala and applying expertise in compiler design and type systems, Alexander replaced the Scala 2 -Xlint:infer-any behavior with explicit diagnostics, guiding developers toward safer type usage. The implementation included comprehensive tests to validate the new warning mechanism and its messaging. This work addressed silent type errors and improved migration feedback, demonstrating a thoughtful approach to enhancing type safety and maintainability within the Scala 3 codebase.