Miller will open the season with Double-A Arkansas, MLB.com reports.
The Mariners don't like sending prized pitching prospects to the Pacific Coast League due to how the conditions mess with pitchers, so while Miller earned a bump this spring and with his performance in 10 starts at Double-A last year, he'll return to Arkansas for now. Seattle jumped George Kirby directly from Double-A to the majors last year, and the same could happen with Miller this summer.