The team announced the news via Twitter:
Of course, with the team holding the No. 5 overall pick and the possibility of either Jameis Winston or Marcus Mariota falling to that slot, general manager Scot McCloughan insisted that picking up the option wouldn't affect the team's draft plans, per Around the NFL and CSN:
It makes sense. If Washington is hoping to entertain trade offers for the No. 5 pick from teams looking to move up and potentially land a quarterback, it needs to give off the impression it could possibly take a quarterback.
Meanwhile, the team can essentially take the cautious approach with Griffin before committing to a full contract extension with him. As Albert Breer of NFL.com explains, that essentially means the team is franchise-tagging him for 2016:
Mike Garafolo of Fox Sports outlined that risk:
In essence, Griffin's contract for next season doesn't become guaranteed until the start of the next league year, unless he is injured. So if Griffin flops this year, Washington can cut him before the next league year without the contract being fully guaranteed. The exception to that is if Griffin suffers an injury that carries into 2016. In that case, Washington will be stuck with the contract.
It's not exactly the biggest vote of confidence in Griffin any way you slice it, but it does make sense from Washington's perspective given Griffin's injury history and his struggles in head coach Jay Gruden's system last season. This is a huge year for Griffin, who needs to rebuild his career and prove he'll be worth a major contract extension or deal with a new team in free agency if he hits the market after the 2016 season.