The 6-foot-2, -210-pound Soto began the season with the Cleveland Indians organization before being traded to the Cubs on April 11 in exchange for cash considerations. He was designated for assignment by the Cubs on October 3 and claimed off waivers by the A's on October 26.
Soto, a native of Carolina, Puerto Rico, has gone 26-28 with a 3.29 ERA (188 ER/514.0 IP), 478 strikeouts and a .235 opponents average over eight minor-league seasons. He also appeared in six games with the Indians in 2015, throwing 3.1 scoreless IP.
Soto originally was selected by Detroit in the 21st round of the 2009 draft before being traded to Cleveland on July 29, 2010 in return for shortstop Jhonny Peralta.
Chicago's 40-man roster increases to 38.