Android Pie has been spreading slowly through Samsung's smartphone lineup in recent months. The Galaxy S9 family got the OTA first, and then the Note 9 began its Android 9 journey early this year. Most Galaxy Note 9 devices should be taken care of with today's rollout for both Verizon and unlocked phones.
Samsung is unusual in the way it handles unlocked phone updates. Most OEMs just push non-carrier updates on their own schedule, but Samsung runs the update through the big four US carriers before delivering it to unlocked phones. Verizon is the last of the big four to get its OTA, so unlocked is coming along for the ride.
The update brings all the usual Android Pie features like adaptive battery and notification management, but Pie on Samsung phones also means One UI. It's a substantial design change with a dark mode, new navigation options, and more. The OTA clocks in at roughly 1.6GB, and Samsung still does not do seamless installations. Thus, your phone will be offline for about ten minutes during the install process.