To the people downvoting this comment: By saying that 11 is what 10 was to Mac OS 9 implies the same substantial changes made to the whole system which is not the case here, at all. Mac OS 10 / OS X / macOS was a completely new system based on NeXTSTEP (or at least, completely different from Mac OS 9). It is still the same operating system, just in the usual upgraded fashion (although this time with more visual changes). By dropping the 10, Apple would have stated that macOS is just considered the successor to Mac OS (9) and the previous major "10" is already implied by the name. The 11 just makes no sense considering there has already been an 11th OS X.