Chainfire has officially released the boot-to-root image for Pixel and Pixel XL devices running the Android O Developer Preview 3 with SuperSu v2.82 SR1. Just a day after Chainfire was successfully able to root Android O Developer Preview 2, the third Developer Preview was released. Luckily, it just took a few lines of code to get it working with the latest preview.
You can find the official boot-to-root images here from Chainfire’s post on XDA. If you would like more of an in-depth read you can find that on Chainfire’s Google+ page. I have personally used the boot-to-root method on my Pixel XL running Android O Developer Preview 3 with no issues.
In order to flash the rooted image, you need the a program such as Minimal ADB and Fastboot, which can be found on XDA.
Here on the instructions on how to boot-to-root:
Boot into the bootloader:
Method 1: use “adb reboot bootloader”
Method 2: Turn off the device. Once powered off, hold volume down and power
Run “fastboot boot boot-to-root.img”
Wait for a few minutes. The device will reboot at least twice
You should be rooted once Android is fully booted up
Be sure to let us know if your Pixel or Pixel XL running the Android O Developer Preview is rooted!