The Red Sox recalled Horn from Triple-A Worcester on Saturday, Julian McWilliams of The Boston Globe reports.
Horn has allowed just one earned run over 5.1 innings since being optioned to Triple-A in late August, and he'll now be called upon to give the Red Sox a fresh arm out of the bullpen. Zach Penrod will make the journey to Boston alongside Horn, forcing Zack Kelly and Cam Booser back to the minors.