[Pixel C General] oRAirwolf:
The instructions in this guide are outdated and way more complicated than necessary. Once the official release of Android 7.0 Nougat becomes available/rooted, I will update the procedures in this thread. In the meantime, I recommend referencing this post along with the original instructions.

A massive shout out to [MENTION=4867279]cheep5k8[/MENTION] for all the hard work he did in getting root and recovery working on the Pixel C. Please donate to him if you can. He deserves it.

Disclaimer: This will wipe your device. Backup anything important before you start. I mostly made this guide for selfish reasons. cheep5k8 has done a great job but some of the instructions are a little vague. I like being spoon fed and I wanted a resource to refer to in the future. You know the drill. If it breaks, not my problem. Post in the forums or hop onto the XDA IRC channel.

There may be more efficient ways to do this, but this will get you where you need to be. If you find any problems or have any suggestions, feel free to reply (BE VERY SPECIFIC WITH STEPS) and I will do my best to update the instructions.

Prerequisites:

ADB/Fastboot - Minimal ADB and Fastboot

ADB/Fastboot Drivers - I recommend using Wugfresh's Nexus Root Toolkit and using the full driver installation guide. Alternatively, you can install them yourself using the official Google Drivers (no installer)

An easy way to access the ADB prompt is to navigate to the directory that ADB is installed in, hold shift and right click inside the directory. This will give you an expanded right click menu that includes an option to "Open command window here." Select this option and a command prompt will open that is already in the ADB directory, saving you from having to do a bunch of cd nonsense. You can check to see if your device is recognized in ADB by typing "adb devices." If ADB and the driver are all working correctly, it should come back with something like "5A20001071 device." You can also check to make sure your device is recognized in fastboot by booting to the bootloader and typing "fastboot devices." It will show something similar.

Necessary Files:

Pixel C Recovery - Cheap5k8's Recovery -- NYCHitman's Recovery (newer)

Pixel C Root files - Download the XCeeD kernel, su.img, and SuperUser.apk

Copy these files to your directory that contains the ADB and Fastboot executables.

Device Prep:

Enable developer mode

Go to Settings > About tablet

Tap on Build Number 7 times until it says "You are now a developer"

Enable OEM Unlocking

Go to Settings > Developer options

Enable OEM Unlocking

Tap on Enable when a disclaimer pops up

Enable USB Debugging (ADB)

Go to Settings > Developer options

Enable USB debugging

Tap on OK when prompted with a disclaimer

If the ADB USB driver has been installed, you will see a popup that says "The computer's RSA key fingerprint is: xx:xx:xx:xx(blah blah)"

Check the box next to "Always allow from this computer"

Tap on OK

Unlock Bootloader:

Open ADB prompt (see prerequisites)

Input the following:

adb reboot-bootloader

The device will now boot into the bootloader and say

Waiting for fastboot command...

Input the following to unlock the bootloader:

fastboot flashing unlock

You will be prompted on the tablet screen with a warning about unlocking the bootloader.

Press the power button to unlock the bootloader.

The device will reboot and say "Bootloader is unlocked and OS verification is OFF. Device will continue booting in 30 seconds." You will also hear an audible beep. You will then see the green android with some spinny stuff. This is the userdata being formatted.

When complete, the device will boot back into the bootloader and say

Waiting for fastboot command...

Boot back into Android by inputting:

fastboot reboot

Your Pixel C will be reset, so you will need to re-enable USB debugging. Connect to your wireless network and then skip past everything else in the initial setup, as all of this setup info will be wiped again later on. Refer to the "Enable USB Debugging (ADB)" steps above to re-enable USB debugging.

Install Custom Recovery:

Open ADB prompt (see prerequisites)

Input the following:

adb reboot-bootloader

The device will now boot into the bootloader and say

Waiting for fastboot command...

With the Pixel C in the Fastboot bootloader and the recovery file in your ADB directory, input the following:

fastboot flash recovery (replace with custom recovery filename).img

Example:

C:\>fastboot flash recovery twrp-2.8.7.0-dragon-ryu-01082016-2.img
target reported max download size of 268435456 bytes
erasing 'recovery'...
(bootloader) erasing flash
OKAY [ 0.054s]
sending 'recovery' (13760 KB)...
OKAY [ 0.349s]
writing 'recovery'...
(bootloader) writing flash
OKAY [ 0.375s]
finished. total time: 0.783s

Reboot into Recovery using the physical buttons. If you reboot the device back into Android, it will write over the custom recovery with the stock one. This will be fixed in the future.

Power + Volume down until screen turns off, keep pressing volume down to boot into Coreboot Bootloader. Navigate to Reboot into Android Recovery with volume down and then press power to select.

Install Root:

In TWRP, navigate to Wipe > Format Data

Type "yes" in the warning prompt and wait for the userdata partition to format. Again, this will wipe your tablet.

Press the Home button at the bottom when the format is complete

Navigate to Reboot > Bootloader to boot back into Fastboot

In the ADB prompt, flash the new kernel:

fastboot flash boot (replace with xCeeD kernel filename).img

Example:

C:\>fastboot flash boot xceed-kernel-google-dragon-02-01-2016-RC1.img
target reported max download size of 268435456 bytes
erasing 'boot'...
(bootloader) erasing flash
OKAY [ 0.064s]
sending 'boot' (6220 KB)...
OKAY [ 0.161s]
writing 'boot'...
(bootloader) writing flash
OKAY [ 0.197s]
finished. total time: 0.426s

Reboot into Android. The device may boot twice.

fastboot reboot

Reboot back into Recovery. Power + Volume down until screen turns off, keep pressing volume down to boot into Coreboot Bootloader. Navigate to Reboot into Android Recovery with volume down and then press power to select.

In TWRP, navigate to Mount and check only Data

In the ADB prompt move su.img to /data:

adb push su.img /data

Example:

C:\>adb push su.img /data
5677 KB/s (33554432 bytes in 5.772s)

In TWRP, navigate to Mount and uncheck Data

In TWRP, navigate to Reboot > System

Perform initial device setup

Once you are at the home launcher, re-enable USB debugging (Refer to Device Prep)

In the ADB prompt, install superuser.apk:

adb install Superuser.apk

Example:

C:\>adb install Superuser.apk
8612 KB/s (6227998 bytes in 0.706s)
pkg: /data/local/tmp/Superuser.apk
Success

Install Busybox from the Play Store: link

Congrats. You are now rooted (not in the Australian sense).