The Pixel C is Google's newest attempt at making a tablet. Like all Nexus and Pixel devices, it has a large number of custom ROMs available for it, but there wasn't actually an official version of TWRP recovery until now.
It's a bit odd that there wasn't official support before from the project, but the tablet now has a page on the project's site. This also means that new versions should be released for the Pixel C at the same time as other devices. See the link below for instructions on flashing the recovery on the Pixel C.