Twins of the Appalachian League, going 0–1 with a 4.91 ERA over 7.1 innings pitched. In 2011, Achter spent the season with the Beloit Snappers of the Midwest League. In his first full professional season, A.J. started 19 games, going 5–8 with a 4.52 ERA. Achter began the 2012 season with the Snappers, this time as a reliever, and quickly found his niche, going 3–1 with a 2.48 ERA over 40 innings. Achter's success earned the pitcher a mid-June promotion to the High-A Fort Myers Miracle of the Florida State League as well as an All-Star selection in the Midwest League. A.J. pitched another 34.1 innings while allowing three earned runs, leading to a sparkling 0.79 ERA to go along with 37 strikeouts and a 2–1 record. As a result of his success the year before, Achter started 2013 with the AA New Britain Rock Cats of the Eastern League, carrying a 2–0 record, 2.21 ERA, and 36 strikeouts over 36.2 innings of work. He was named to appear in the Eastern League All-Star Game. Achter was promoted to the AAA Rochester Red Wings of the International League. While in Rochester, Achter went 1–2 with a 3.04 ERA, .198 batting average against, and 20 strikeouts over 23.2 innings, helping the Red Wings to their first playoff appearance since 2006. He was assigned to the Arizona Fall League after the season. In 2014, Achter began the year at AA with the New Britain Rock Cats but did not remain there for long; after 6.2 scoreless innings in which Achter allowed three hits, one walk, and struck out 11, he was promoted to the AAA Rochester Red Wings where he was the only Red Wings' player selected to the 2014 AAA All-Star Game. On September 1 his contract was selected by the Twins and he was called up the Majors for the first time in his career. Two days later he made his Major League debut against the Chicago White Sox, pitching one inning in relief and not allowing a run. Los Angeles Angels After the 2015 season, the Philadelphia Phillies claimed Achter off of waivers. They designated him for assignment on December 11. On December 17, 2015, Achter was claimed off of waivers by the Los Angeles Angels. He began the season with the AAA Salt Lake Bees. The Angels selected his contract on August 9, 2016. During the 2016 season,