They are not doing Semver. They are just counting two number, e.g. after 4.9 there is 5.0. Afaik, every version can contain breaking changing.

Does that mean I'm supposed to interpret "... oh wait..." as "it would be very easy for them to deprecate a feature because they have lots of sufficiently major releases"? Because it comes across as implying they wouldn't be able to do it.

I really don't understand what GP's point was.

I'm not trying to be cheeky here. They have literally joked about how TypeScript versions means nothing really. So they can't just announce a new major version and drop enums completely. Maybe with a feature flag this is possible but even then, a fresh tsc --init not supporting enums is not really how TypeScript works

But they do break things and drop things. I don't see why they can't do that. I think they simply don't want to remove it very badly.