On October 20, 2017, the Minnesota Twins signed Teng for a $500,000 signing bonus.[2] He made his professional debut with the rookie–level Gulf Coast League Twins in 2018, making 10 appearances (9 starts) and posting a 3.59 ERA with 47 strikeouts in 42+2⁄3 innings pitched.[3]
He began the 2019 season with the Cedar Rapids Kernels of the Single–AMidwest League, and was named the league's pitcher of the week for the week ending July 14.[4] In 9 games for Cedar Rapids, Teng logged a 4–0 record and 1.60 ERA.
On June 2, 2021, while pitching for the High–A Eugene Emeralds, he was suspended for 10 games after umpires found a foreign substance in his glove.[7] In 21 starts for Eugene, Teng recorded a 4.33 ERA with 142 strikeouts in 95+2⁄3 innings of work.[8] Teng spent the 2022 season with the Double–A Richmond Flying Squirrels, making 28 starts and registering a 6–12 record and 5.22 ERA with a career–high 169 strikeouts in 136+1⁄3 innings pitched.[9]
Teng began the 2023 season back with Double–A Richmond, starting 12 games and posting a 4.75 ERA with 68 strikeouts in 47+1⁄3 innings of work.[10] On June 18, 2023, he was promoted to the Triple–A Sacramento River Cats.[11] In 17 games (16 starts) for Sacramento, Teng logged a 6–5 record and 4.22 ERA with 96 strikeouts across 76 innings pitched.
On November 14, 2023, the Giants added Teng to their 40-man roster to protect him from the Rule 5 draft.[12][13] He spent some time in major league spring training,[14] and was optioned to Triple–A Sacramento to begin the 2024 season.[15] On March 29, 2024, Teng was promoted to the major leagues for the first time.[16][17] Teng made his major league debut in relief of Daulton Jefferies, pitching three innings while yielding four hits and three runs.[18][19] In 4 games during his rookie campaign, he struggled to a 9.82 ERA with 7 strikeouts over 11 innings of work. Teng was designated for assignment by San Francisco on November 19.[20] On November 22, the Giants non–tendered Teng, making him a free agent.[21]
On November 29, 2024, Teng re–signed with the Giants organization on a minor league contract.[22]