The main forte of using a Google branded phone is the presence of near stock Android OS. If you're an avid Android customizer, then you can head over to XDA Forums and download a custom ROM to enhance the usage of the device.
However, one of the famous custom ROM CopperheadOS is directly selling the Pixel XL and Pixel with the OS preloaded. The specialty of CopperheadOS is the security it offers. Although Google is pushing monthly security patches and regular software update, CoopperheadOS claims themselves as the more secure than the Google' stock Android.
The CopperheadOS is available for various Google-branded devices, but if you want a Pixel phone which is more secure than ever, you can purchase the device from CopperheadOS store. Also, the phone is available to purchase only in Canada and the US.
There are no details regarding the availability of Pixel XL from the CopperheadOS store, but indeed, the store is selling the Pixel for $1049 (32GB option), whereas the 128GB one costs $1149.