The Orioles added four prospects to their 40-man roster Wednesday, protecting them from next month’s Rule 5 draft while leaving room to make other moves between now and the winter meetings.

The four prospects — infielder Ryan Mountcastle, left-hander Keegan Akin, right-hander Dean Kremer, and outfielder Ryan McKenna — stretch the roster to 39 players and represent some of the best prospects in the Orioles’ high minors. They’re pieces that, while now on the roster, might end up being long-term contributors to the organization.

Mountcastle, 22, was the International League Most Valuable Player for batting .312 with an .871 OPS and 25 home runs in his debut last summer at Triple-A Norfolk, with the team continuing to find a defensive home for what will assuredly be a productive, middle-of-the-order bat.

Akin also spent all of last year at Norfolk working on his secondary pitches, and had a 4.73 ERA in 112 1/3 innings there. A former first-day draft pick, Akin has used a sneaky fastball to get through his career, though the team is asking more as he looks to compete for a 2020 rotation spot.

Kremer was one of five pieces added in the 2018 trade with the Los Angeles Dodgers for Manny Machado and continued the success that made him an attractive trade piece. While he missed spring training with an oblique injury, Kremer had a 2.98 ERA at Double-A Bowie, struggled some at Norfolk, then dominated in the Arizona Fall League to set himself up for a bright future.

It wasn’t as successful a year for McKenna at Bowie, though, despite it coming off a breakout season and good spell in Arizona. McKenna’s bat didn’t shine as he struggled some for the Baysox, though his speed and defensive value make him the type of player the Orioles will want to keep and help develop.

A pair of notable pitchers were not added to the roster as well, with 2016 first-round pick Cody Sedlock and 2015 bonus baby Gray Fenter left unprotected. Sedlock had a bounceback year and had a 2.84 ERA over two levels in 2019 after two years of injury struggles, while Fenter had a 1.81 ERA with 123 strikeouts in 94 1/3 innings at age-23 at Low-A Delmarva.

Those players will be eligible to be selected in the Rule 5 draft on Dec. 12 at the winter meetings in San Diego.