watchOS 6 will have a total of 6 new watch faces and several customization options for those who own the latest Series 4 model.

Apple Watch Series 1 to 3 owners can still get the update but they’re only limited to 2 new watch faces- the Numerals Duo and Numerals Mono. The two faces offer customizations on style, typeface and color but they’re largely limited to telling time.
Apple Watch Series 4 owners get 4 more new faces with support for displaying more information via complications, e.g., California, Gradient, Solar Dial and Modular Compact.
Apple has made these exclusivity moves before- the Explorer analog is still unique to Apple Watch Series 3 and 4 LTEs, while Hermes and Nike models get their own special watch faces.
Those who are thinking of upgrading can enjoy the new model’s faster performance, larger screens, louder speakers, a built-in ECG monitor and fall detection.
watchOS 6 is currently in beta stages and is expected to be released to the public in fall.