Sony Mobile just started rolling out Android 7.0 (Nougat) update for the Xperia Z-series smartphones, starting from the Xperia Z5 and Xperia Z5 Premium with build number 32.3.A.0.372, and now the Xperia Z3+ and Z3+ Dual are getting the exact same update with the same firmware build.
The Android 7.0 brings new multi window support, longer battery life, improved messaging app, new notification panel and more. Sony has also added new features such as new Xperia Home launcher with Google Now integration, new self-timer button to the front camera interface, STAMINA mode with three new power saving levels and more.
The OTA (over-the-air) update is about 1.3GB in size and it will be gradually rolling out for all the users globally. Notification for the update should automatically pop up on your device when it is available for you or, you can check it manually by heading to Settings -> About Device -> Software Update.