His father, Trevor, confirmed that he gave the Huskies a commitment.
Yankoff, the top skill prospect in Idaho and the first four-star quarterback from Idaho since 2012, joins Jacob Sirmon as Scout 300 prospects in the Huskies' 2018 class.
A former commit to Oregon, Yankoff opened his recruitment when Mark Helfrich was let go last fall.
Washington had continued to recruit him despite having a commitment from Sirmon, wanting two quarterbacks in the 2018 class.
Yankoff took an unofficial visit to Washington in February and the offer from the Huskies was extended.
And on Wednesday night, Yankoff committed to Chris Petersen and Jonathan Smith.
Scout went out to Idaho last October to watch Yankoff in person.
Season Scouting Report: Yankoff is the top skill prospect in Idaho in the 2018 class. Against Lake City (Idaho), he had another big game, running for three touchdowns and throwing for two more. Yankoff has the ability to find receivers and spread the ball around but also make plays with his legs. He's got pretty good speed and can take a hit, but also shows good patience in going through his reads instead of just quickly tucking and running. We've seen a lot of Yankoff in camp settings, but he's at his best on Friday nights where he can show his dual-threat ability. -Huffman
Yankoff is the fifth member of the Scout 300 to commit to the Huskies in the 2018 class.