Swanson was sent to Triple-A Tacoma on Sunday, Shannon Drayer of 710 ESPN Seattle reports.
Swanson received an invite to major-league camp after finishing his 2018 season in Triple-A. He posted a 3.86 ERA and 1.07 WHIP with a 78:14 K:BB over 72.1 frames. After picking up some valuable experience in big-league camp, he'll head to Triple-A in preparation for the upcoming season.