The Capitals acquired the pick from the Winnipeg Jets on Monday in a trade for defenseman Brenden Dillon.
Vanecek returns to Washington after being selected by Seattle in the 2021 NHL Expansion Draft on July 21. The 25-year-old was 21-10-4 with a 2.69 goals-against average, .908 save percentage and two shutouts in 37 games (36 starts) for the Capitals last season.
The Kraken signed goalie Philipp Grubauer to a six-year, $35.5 million contract Wednesday.
Grubauer was 30-9-1 with a 1.95 GAA, a .922 save percentage and seven shutouts in 40 games (39 starts) for the Colorado Avalanche last season, when the 29-year-old was voted a finalist for the Vezina Trophy as the top goalie in the NHL.