The move allows lefthander Felix Doubront to become the team’s fifth starter at the beginning of the season.
Hahn posted a 11.15 ERA this spring, as opponents batted .382 against him.
The 26-year-old pitched in 16 games for Oakland last season, going 6–6 with a 3.35 ERA and 64 strikeouts before being shut down because of arm injuries. In two MLB seasons, Hahn has accumulated a 13–10 record and a 3.23 ERA with the A’s and San Diego Padres.
Oakland’s starting rotation to begin the season will consist of Sonny Gray, Rich Hill, Kendall Graveman, Chris Bassitt and Doubront.