Android 9.0 Pie brings new gesture navigation that replaces three software nav buttons. This new gesture-based navigation requires you to swipe back and forth between apps and menus. This new navigation method is optional on the Pixel and Pixel 2, but Google has confirmed that it is default on the Pixel 3.
The new gesture-based navigation system cannot be disabled or swapped either. Google on Twitter said that “Pixel 3 introduces a new pattern that will represent navigation on all Android phones going forward, the tweet said. “While change & adapting to new patterns is hard, we believe it’s a better navigation pattern & makes app switching a faster experience.”
Hi! Pixel 3 introduces a new pattern that will represent navigation on all Android phones going forward. While change & adapting to new patterns is hard, we believe it’s a better navigation pattern & makes app switching a faster experience.
— Made by Google (@madebygoogle) October 9, 2018
However, this doesn’t come as a surprise especially since it is enabled by default on the new phones with Pie. So, if you were hoping on using the classic nav buttons on your Pixel 3, this might be a bit disappointing.