How is that not an implementation detail? You can't really inspect the stack at runtime in a useful way. It's literally just performance and yeah you might run

How is that not an implementation detail? You can't really inspect the stack at runtime in a useful way. It's literally just performance and yeah you might run out of memory somewhere but that's true of every language detail, some languages are more efficient than others. I'm getting downvoted but I think my comment stands. Clojure is a perfectly useful example of a language without TCO. It's not necessary, it's a detail. And as a long time developer, there hasn't been a single time where I cared if my stack took constant space or not. It has never mattered.