The iPhone XS Max runs iOS 12, Apple's latest smartphone OS. It includes new apps like Measure and Siri Shortcuts, grouped notifications, and new emoji (coming in an update later this month).
The Pixel 3 XL runs a stock version of Android 9 Pie straight out of the box. That means it has Google's latest smartphone operating system, but it also doesn't have any unnecessary layers, or skins, on top of it, unlike so many Android phones from other phone makers.
Both devices also have a built-in smart assistant: the iPhone XS Max has Siri, while the Pixel 3 XL has Google Assistant.