The Atlantic League has been designated the first MLB Partner League, extending the independent circuit’s relationship in terms of rules testing into areas like joint marketing and promotional opportunities.

Prior to the 2019 season, MLB and the Atlantic League announced a three-year agreement that calls for the independent circuit to serve as a testing ground for various rule and equipment changes being explored by MLB. A number of ideas were tested in the Atlantic League as a result of that agreement, though some, like the implementation of Trackman automated ball-strike (ABS) technology, came under heavy criticism. In addition, the Atlantic League tested rules limiting defensive shifting, mound visits, shortening inning breaks, and larger bases, while others, like moving the mound two feet farther from the plate, were postponed.