He also received an invitation to spring training.
Iwakuma, 36, was 0-2 with a 4.35 ERA in six starts last season. He was placed on the disabled list on May 10 with shoulder trouble and didn't return. He had surgery on his right shoulder on Sept. 27. The Mariners said at the time that he wasn't expected to resume throwing for five months.
He has a career record of 63-39 with a 3.42 ERA in 150 games, all with the Mariners, over six major league seasons.