As other people have said, userland ABI/API is solid. I should have clarified that. There is no reason the internal API would be as to be honest it's the Kerne

As other people have said, userland ABI/API is solid. I should have clarified that. There is no reason the internal API would be as to be honest it's the Kernel's job to make the drivers sit behind that API and stay there regardless of the problems. That is the abstraction boundary. The issue is where the abstraction boundary is. In NetworkManager for example, which is an example I'm probably just picking on, there are many more abstractions above the kernel's abstraction which are unstable. Again, comparing to Windows, there have been several driver model revisions but the userland API+ABI is stable between them.