[Google Pixel 2 XL Guides, News, & Discussion] thomasamas:
PLEASE READ MY IMPORTANT NOTICE ABOUT 8.1 BELOW

See update as well!

Hey, guys! This is my first thread ever, so please give me some grace. (I do not know all the formatting stuff yet)

I decided that because I had to wipe my Pixel 2 XL twice in the process of trying to figure this out, I may as well write a quick tutorial on how to do this the easy (and mostly safe) way.

This is where they all insert the disclaimer:

This tutoial is based on software I did not write or contribute to in any way, If you have issues with it, contact their respective developers, Google can help with this. DO NOT blame me for your now-a-fancy-paperweight-pixel,
I have diplomatic immunity and will tell you to contact my lawyer who doesn't care. You risk what you risk, take responsibility for that.

Now for the meat....

What you need:

Unlocked bootloader with MAGISK ROOT (other root may work, only tested magisk beta)

The Latest OTA File from the official download page, saved to your device

The Flashfire App by one of the greatest XDA legends of all time, Chainfire

The flashable zips for Magisk and any other stuff you want installed (like a custom kernel) when the update gets flashed (typically magisk modules do not need to be reflashed, they stay installed)

Advisable: nothing that has modified your system partitions (

only

have systemless mods like magisk)

Now that you're all set:

Open Flashfire and grant it root permissions.

Tap through all the warnings

Hit the plus sign and hit "Flash ZIP or OTA"

Find your stored OTA file you downloaded from the Google OTA page.

Check all three available options, (Auto-mount, Mount system..., and Restore Boot and Recovery)

Repeat step #3 with your newfound ability to flash zips, add a kernel (I use Flash Kernel) and flash the newest official magisk beta the same way. NOTE: Check boxes for these shouldn't need to include "auto-mount" or "restore boot and recovery images"

DISABLE ever-root settings completely from the flash queue.

Click the red lightning button at the bottom left.

Give it up to 5 minutes to do its business.

Reboot and profit.

If that didn't make sense, watch my simple video!!

(there is one mistake in the video, on all other things than the OTA itself, DO NOT check the box for restoring stock boot and recovery)

NOTE: You are unable to flash recoveries through this method, I've tried it and so far no luck. We may be able to later when apps let us flash the boot partition properly but for now, it won't stick.

Credits:

Chainfire for his amazing flashfire app!

Team Pixel for their awesome phone.

XDA for all the years of being awesome.

topjohnwu for magisk badassery

If you should be credited, PM ME.

IMPORTANT NOTICE:

Magisk beta thread clearly states that currently (12/05/2017) Magisk 14.5 with official pixel support is only tested up to 8.0, NOT 8.1 yet. Due to this and the fact that aosp 8.1 is super duper new and most kernels likely don't have an 8.1 version, I'd recommend waiting till this post is updated to flash anything 8.1

UPDATE 12/29/2017: As of now flashfire works for some things on oreo, but Ill need to look into it after we get another Oreo update to see if it can be flashed from there, however this may become obsolete assuming you can just use magisk's new features to do updates the official way. (google it)

That's all, Folks!

If this helped you, SMASH that thanks button! Also, Please try to keep OT stuff to a minimum.

I'll be posting a video soon that shows the flashfire process in a little better detail. Posted it, in the instructions!!