[tazjin]

How does this interact with third-party dependencies you use? In my experience, most gradual typing things break down at that boundary.

[seabrookmx]

This isn't gradual typing? If libraries are not compiled with the compiler option, then all their reference types will be deemed nullable and I need to check for null before dereferencing. I can't do something like "GetItem().Name" if "GetItem()" returns a reference type like I could in Java, GoLang, JS, etc. If that library did use the flag and was provably non-nullable, then I could.