At which point do you consider it OK to NOT use typing for a library, or any piece of code that another programmer is going to have to use or maintain ?

I think basically never ( even for throwaway code, because they often end up being reused). So i’d much prefer a language for which static typing is not an afterthought..

Who is using gradual typing in a clojure codebase? I've never seen any usages of core.typed in the wild. Using schema is more common although its future seems uncertain in the wake of spec. In my experience schemas require just as much effort as specifying types without the benefit of automatic checking or the usual IDE integrations like navigation or autocompletion. As a result they're rarely used widely enough to be useful.