At this point, almost all community and all standard library APIs use nullable reference types (and types that aren't NRTs are obviously expected to always have

At this point, almost all community and all standard library APIs use nullable reference types (and types that aren't NRTs are obviously expected to always have a value). This change in F# makes it able to interoperate with C# NRTs, where C#'s T? becomes F#'s T | null and vice versa. I feel like the ease of integration of F# into existing codebases is one of the major selling points. You don't need to write wrappers in order to consume most existing C# code, which, for example, enables writing a core with business logic in F# while keeping the IO in C# if necessary.