C# is an interesting case because it shares a common runtime with F#, and F# guarantees TCO in most circumstances ( try / catch can stop it ) .

There is a "tail" prefix in the intermediate language (IL) bytecode that F# uses but Roslyn, the C# compiler, never emits.

So unlike F#, whether the same algorithm written in C# becomes a loop depends on JIT behaviour. This means if you're coming to a function cold in C# you can overflow the stack, while if you enter the same function fresh after it's been warmed up, it may have been optimised away by RyuJIT and if so you are able to call it safely for what would be large numbers of recursions.