>There's hardly any other API with that kind of backwards compatibility.

Qt? 99.99% of the API from Qt 4 (2005) is identical in Qt 6 (ongoing). A few headers were renamed, and a few minor functions, generally stuff you can port in 1 day.

When they released Qt 5 and 6 and decided to switch from Qt Widgets to a new GUI toolkit (QML), they didn't say "umm, just rewrite your whole codebase in QML bro", they kept widgets around in perpetual maintenance mode. This is how you respect your users.