High-A

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The 1965 hierarchy was in place for 25 years, until Class A was further subdivided in 1990, with Class A-Advanced becoming the third-highest classification:

1. Triple-A
2. Double-A
3. Class A-Advanced
4. Class A ("Full-Season A")
5. Class A Short Season ("Short-Season A")
6. Rookie league

Three Class A leagues received the Class A-Advanced designation: the California League, Carolina League, and Florida State League. This arrangement continued until 2021, when Major League Baseball (MLB) restructured the minor leagues, eliminating Class A Short Season and discontinuing the use of all historical league names within Minor League Baseball. The existing Class A-Advanced leagues were moved to the Class A level and operated under generic names (Low-A West, Low-A East, and Low-A Southeast) during 2021. The Class A-Advanced level was officially renamed as "Class High-A", and also operated three leagues during 2021 with generic names: High-A Central, High-A East, and High-A West. These three High-A leagues had historically been known as the Midwest League, South Atlantic League, and Northwest League—the first two had previously operated at the Class A level, while the latter had previously operated at the Class A Short Season level. Following MLB's acquisition of the rights to the names of the historical minor leagues, MLB announced on March 16, 2022, that the leagues would revert to their prior names, effective with the 2022 season.

In January 2023, it was announced that Veronica Gajownik had been hired to manage the Hillsboro Hops, making her the first woman to manage a High-A team.

However, with only six clubs in the Northwest League, the format for the postseason will consist of a single, best-of-five championship series. The two playoff participants will be decided based on the best winning percentage of each half. In the event the same club wins both halves, the club with the next-best winning percentage in the second half will advance.

In the event of any ties, the following tiebreakers will apply in the order below:

1. Head-to-head record between the clubs in the respective half (if three or more clubs, best winning percentage in games among the clubs).
2. If the clubs remain tied, best overall winning percentage over the last 20 games.
3. If the clubs remain tied, best overall winning percentage over an additional game (i.e., the last 21 games, the last 22 games, etc.) until one emerges with a better winning percentage in that span of games.