Samsung hasn't detailed its roadmap as yet so it's unclear when it will release Android 9.0 for Galaxy S9. However, an early build of Android 9.0 for the Galaxy S9 has been leaked online. It shows that major user interface changes are part of this update. It brings Samsung Experience 10, the next iteration of Samsung's custom skin for Android.
Since this is an early build, some user interface elements are incomplete and a few features are broken. As you can expect from a build this like there are bugs as well. Nevertheless, it does give us a good idea of what to expect from Android 9.0 for Galaxy S9.
Leaked early build of Android 9.0 for Galaxy S9
The new AMOLED dark theme is one of the biggest user interface changes in this update. Android Pie brings a dark theme and Samsung is calling it the night theme. It's broken in this build as it can't be switched off. There would obviously be an option to enable and disable the night theme in the final version. The options will allow users to manually enable it, have to enable automatically at a scheduled time or have it enabled automatically after sundown.
The card-style user interface that Google demonstrated during I/O 2018 is also present. The Quick Settings shade has been redesigned as well in keeping with this design language. The buttons are rounded and many of the options can be managed without having to open the Settings app.
The Android Pie flavor is also evident in the recent apps menu on Samsung Experience 10.0. There is a dock at the bottom now with the recent apps scrolling horizontally and not vertically like before. It has already been possible to get this using Good Lock on Samsung devices.
Gesture control is also included in this build of Android 9.0 for Galaxy S9. They're not exactly the ones that Google has developed for the firmware. Users will be able to swipe up from the bottom in the position where the Home, Back and Recents buttons are located.
This gesture is enabled only when the navigation bar is hidden. A new motions and gestures menu has been added as well. It lists all of the previous gestures such as palm swipe to capture. There's a new lift to wake feature which will wake up the device when it's picked up.
Native apps updated
Samsung has also updated many of its native apps in Samsung Experience 10.0. The dialer app gets the night theme as well. Buttons for contacts, keypad and recent have been moved to the bottom. The Messages update has been updated with the curved design and its buttons have been moved to the bottom as well.
There are user interface changes for Bixby Home as well. The design is similar to other updated system apps as it also gets curved borders and the night theme. This Android 9.0 for Galaxy S9 build doesn't have any new Bixby Home features but that could change in the future. Other apps such as Mail, Gallery and Camera have all been updated too. The new camera app brings a couple of new options which don't seem to be working in this build.