The Mac operating system is quite mature and rarely gets significant updates, but the rumored redesign may push macOS 16 in a new direction. Apple will undoubtedly provide a place name in California for the release, but that won't be known until WWDC on June 9.
So far, the leaks have focused on iOS 19 and a potential redesign that will bring operating systems closer to the visionOS glass and transparency aesthetic. Mockups show reflective buttons and windows across system apps.
Since the design unification is happening across all operating systems, it is likely that macOS will see similar changes to its UI. It isn't yet known how far the changes will go, but macOS 16 could look dramatically different from macOS Sequoia.
Beyond design changes, there's not much else that can be predicted beyond polishing existing apps and systems. The new app tiling system and Stage Manager could be updated, and System Preferences could continue to be tweaked.
Apple Intelligence is likely to be a significant focus of the developer conference as well. The delayed contextual features will likely be shown off again, but hopefully with more polish.
macOS 16 will be revealed during WWDC 2025 on June 9.