The Xperia XZ in our office is running Android 6.0.1 Marshmallow, and that's what retail units will ship with out of the box. An update to Nougat is planned, naturally, and recent speculations point to an October date.
Sony tends to keep the stock Android look, except for a few gentle touches here and there. The big stuff, like the proprietary Stamina battery saving modes and the home-baked multimedia apps are here as well.
The fingerprint reader introduced on the Z5 series of Xperias is integrated into the Power button on the right side.
We had an excellent user experience with the fingerprint reader on the Xperia XZ. It's fast and accurate. There's an animation that slides the lockscreen away from your thumb (as if you pushed it out of the way). If you have simple swipe unlock enabled (no security) you can tap on the Power button to unlock instead, provided you've woken up the device first.
Smart Lock gives you conditional security - trusted nearby devices, locations, faces, or voices can allow you to skip the security unlock protocol.
The homescreen appears unchanged from the rest of the X series. This includes the swipe down gesture, which shows a screen of the apps you use most along with recommendations for new apps to install. The search field is highlighted so you can start typing the app's name immediately.
The traditional app drawer is present, and you'll find a number of proprietary apps pre-installed. Sony takes great pride in the A/V prowess of their devices, and the multimedia apps are all custom and feature-rich, but more on them in their dedicated chapter.
The app drawer is quite functional as well, letting you sort the apps in by frequency of use, name, date installed or a custom arrangement. The app search works here too, and you can go into a management state, allowing you to uninstall multiple apps instead of having to drag each one to a virtual waste bin.
Themes are available (both free and paid) that can customize the look and sound of the Xperia XZ. Some themes are even interactive with wallpapers reacting to your touches.
The notification area is plain Android. You can re-arrange the quick toggle tiles and adjust the screen brightness. What's missing is a toggle for Auto brightness (you need to go into the settings for that). That's the single thing we don't mind getting changed by manufacturers and still, many of them like to keep this aspect stock.
The app switcher is similarly a vanilla Android affair with the 3D rolodex look and a kill-all button. The small apps are gone, however, and there is no longer floating-app multitasking. There isn't screen pinning either like we had on the Xperia X Performance - apparently, not a very popular feature, as we haven't seen it since.
The Smart cleaner feature will periodically empty the cache of apps you haven't used in awhile. You can switch this off or just manually tell it not to bother for certain apps.
Sony has a proprietary backup solution built-in on its latest Xperias. It can backup applications, contacts, messages, phone settings. The backup info itself can be stored in the cloud under your Sony online account, or locally on the microSD card or an external USB device.
Backups can be scheduled, including conditions like "Connected to Wi-Fi" and "Charging device", depending on your preferences.