Tap-to-wake is one of the niftier features Google's implemented on the Nexus 9, but its telephony-enabled sibling didn't get the same treatment. We know that it almost did, though, thanks to a commit to the device's source code made on September 10th. (We also pointed this out in our review of the Nexus 6).

Google hasn't commented on this other than to make clear that tap-to-wake is not a feature of the Nexus 6.