The Pixel and Pixel XL will be rootable, Google confirms
The folks over at WonderHowTo have reached to Google to inquire on the matter and got official confirmation from Google spokesperson Iska Saric:
Yes, Pixel owners who purchased the device from the Google store will be able to root their devices. Pixel phones purchased from the Google store will ship with an unlockable bootloader.
Unlockable bootloaders mean that the floodgates for custom recoveries and auto rooting tools will be wide open on day one, and developers will no doubt get cracking on it immediately.
Unfortunately, rooted Pixel phones won't be able to receive OTA updates, which is a huge downer, but this has been the case with Nexus devices as well. Rooting entails modifying partitions, and if the update utility detects modified partitions, OTA updates simply fail to apply.
via WonderHowTo
Things that are NOT allowed: