If you want to root your Pixel XL on Anroid 8.0 systemlessly, you can easily do this by using the step by step guide created by XDA Senior Member GroovinChip. This method is tested and found safe but TechGuar will not be responsible for any damages, therefore we expect you to take responsibility and properly understand and follow the step by step guide below.
1) Download the modded TWRP
2) Download SuperSU
3) Download SuperSu Config
4) Download SuHide
5) Copy the modded TWRP to PlatformTools. Rename it however you like. I’m using twrp-oreo for now.
6) Copy SuperSu, SuperSuConfig, and SuHide to internal storage
7) Boot the device into bootloader – adb reboot bootloader
8) Boot into TWRP – fastboot boot twrp-oreo.img
9) Flash SuperSuConfig, then choose add more zips. Choose SuperSU.
10) In the Aroma installer for SuperSuConfig, choose Systemless SBIN. For all other options, I chose let SuperSu decide.
11) Boot to system
12) Go back to bootloader and boot to TWRP
13) Flash SuHide
You can enjoy your rooted Pixel XL now.