iPhoneX and iPhone 8 keyboard height are different

While Craig’s answer is correct, you might not want to pin your view to view.bottom or the bottomLayoutGuide rather than the safe area bottom (especially if your keyboard is not always open, and you don’t want your views to cover the Home Indicator area).

Here is a fix for these cases. It deducts the height of the bottom inset of the safe area from the height of the keyboard:

var keyboardHeight = ... // Get the keyboard height from keyboard notification

if #available(iOS 11.0, *) {
    let bottomInset = view.safeAreaInsets.bottom
    keyboardHeight -= bottomInset
}