When Apple released macOS Big Sur last week, it became the first version of the OS since 2001 to get a major version number bump. It started out in 2001 as Mac OS X, then became OS X, and finally landed on macOS, but throughout all those years, it was version 10. macOS Big Sur was the first one to be version 11. Possibly due to the big visual overhaul, the support for Apple's custom ARM processors, or both, this was seen as the biggest release of macOS since Mac OS X.
Interestingly, Apple released the first developer beta for macOS Big Sur 11.1 today, and that marks another major change for the OS. Over the 19 years of version 10, new releases were marked as minor upgrades, such as 10.1, 10.2, and so on. An actual minor update would increase the build revision number, such as 10.0.1, 10.0.2, and so on.
Calling this macOS 11.1 means that Apple is now marking version numbers in the same way that it's already doing for the rest of its operating systems. It also means that at WWDC next year, the Cupertino firm will be announcing macOS 12, rather than macOS 11.1.
As for what's new in this developer beta, that's unclear. The release notes only show some known issues with accessibility, Catalyst, and software updates.