Just announced on Twitter (showing up elsewhere as well)

@MarkMaske

Redskins announce they will exercise 5th-year option in the contract of QB Robert Griffin III for the 2016 season, worth $16.155 million.
Not sure what to make of this, initial reaction is that they don't seem to want to admit their mistake. I would think they could've extended him for a year much more cheaply than $16M, and waited until halfway through the coming season to do so. There's a risk he plays like a house on fire and they have to pay him $20M, but you think that's a risk worth taking.