[ygra]

C# has never added new reserved keywords. All keywords added after 1.0 are contextual and can still be used as identifiers. With some things like nameof, they even get their special meaning only if there's nothing else of that name that could be called. They take backwards compatibility of existing code quite serious. In fact, the only instance I can remember where C# had a breaking change was in C# 5 with how the foreach loop variable interacted with closures. The probability of code existing that relied on the old behaviour is probably really low, though.

[zenexer]

There have been breaking API changes--.NET Core and the upcoming .NET 5 being good examples--but they're generally handled well. I can't recall any major breaking language changes, though.

They don't let backwards compatibility keep them from introducing new features and syntaxes, which is quite nice. Most languages that want to avoid breaking backwards compatibility seem too hesitant to introduce new language features.

[ygra]

That's why I was referring to C#, not .NET.