The deal includes a vesting option that could make it a two-year deal worth approximately $8 million. The details of the option are unknown, but Rosenthal reports that it can be reached if Downs pitches a "normal workload."
Last season, Downs posted a strong first half for the Angels with a 1.84 ERA and a 1.26 WHIP in 29.1 innings. That success led to trade interest in July, and the Angels shipped him to Atlanta for right hander Cory Rasmus. Some of Downs' advanced metrics (ERA predictors like FIP and xFIP) actually improved in his time with the Braves, but an extreme .432 batting average on plays in play skewed his on-field results. He was still useful, putting up a 3.86 ERA in 14 innings for his new club.
The White Sox will presumably plug Downs into the bullpen spot vacated by Matt Thornton. The team traded Thornton to the Red Sox at last year's deadline, and he recently signed with the Yankees on a two-year, $7 million deal as a free agent.
Despite his brief shortcomings in Atlanta, Downs became one of the league's most prominent LOOGYs with Los Angeles, posting a 2.10 ERA in 128.2 innings for the Angels. He could also compete for the club's closer role, which opened up when Chicago traded 2013 closer Addison Reed to the Diamondbacks for their baseman Matt Davidson.