Sony, a few days ago, made good on its promise to send out the Android Pie update to its devices by October. The Xperia XZ2 and XZ2 Compact kicked off the Pie rollout, although users have claimed that a few major features are yet to be implemented.
https://www.notebookcheck.net/The-Xperia-XZ2-and-XZ2-Compact-receive-Android-Pie-but-there-are-a-few-features-missing.338160.0.html
Glancing at the XZ3 reviews it seems like Sony has no plans to implement gesture control or Android Pie's recent apps screen into its phones.
Not only gestures. XZ2 (H8296) doesn't have Pie update. There is no plans too. They make a fuss only.