This is image that's been posted onto the Google I/O 2014 website, and has been making the rounds today as Google somehow being dumb enough to accidentally leak an unannounced product in an official production. Just take a moment to note the placement of the front-facing speakers, the volume rocker at the bottom corner, and the gentle curve of the sides. This is not a Nexus 8 or a next-generation Nexus 10. This is the Nexus 10 of 2012, running a Jelly Bean version of Android, playing the Chrome Racer game that was demoed at Google I/O 2013. Oh, and that image has been on the Google I/O 2014 website for over a month.
We're expecting many things at Google I/O 2014. A Nexus 10 running Jelly Bean is not one of them. Nothing to see here, move along.
Source: Google I/O