Sony starts rolling out Android 9.0 Pie update for the Xperia XZ2
Apparently, the update is about 1GB in size and includes the October security patch. Apart from that and Android 9.0 Pie, there are no other mentions in the official changelog attached to the update.
If you're rocking a Sony Xperia XZ2, you should be looking for the new firmware version 52.0.A.3.27, which will update your phone to Android 9.0 Pie.
Besides Xperia XZ2, Sony announced that the following devices will be updated to Android 9.0 Pie in the not so distant future: Xperia XZ2 Premium, Xperia XZ2 Compact, Xperia XZ1, Xperia XZ1 Compact, Xperia XZ Premium, Xperia XA2 Plus, Xperia XA2, and Xperia XA2 Ultra.