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Fadell, known for leading production of Apple's first iPod, will advise Glass's current leader, Ivy Ross, while still juggling all his responsibilities at Nest.
Google Glass has had a tough reception. The $1,500 device still hasn't taken off, in part because of its limited release and lack of practical uses.
Glass was the first project ever to emerge from Google X - and one particularly important to Google cofounder Sergey Brin, who runs it - so the team's departure from the lab is even more significant. Fadell's new role suggests that Brin and CEO Larry Page put a lot of trust in him.