Cubs Promote Two Rising Prospects to High-A

The Chicago Cubs organization made a pretty significant move, promoting two up-and-coming prospects from Single-A Myrtle Beach to High-A South Bend. 

The Cubs reportedly promoted both outfielder Josiah Hartshorn and starting pitcher Mason McGwire to the South Bend Cubs. Hartshorn is the team’s No. 8 prospect on MLB Pipeline, while McGwire is unranked. 

Both prospects are deserving of the promotion following a strong start to the season at Single-A. 

Hartshorn continues to be one of the biggest risers on prospect rankings in the Cubs' farm system. The 19-year-old is ranked as Chicago’s No. 8 prospect on MLB Pipeline, No. 6 on FanGraphs, and No. 5 in ESPN’s latest prospect update. 

The Cubs selected Hartshorn in the sixth round of the 2025 MLB Draft as a high schooler. After not appearing in any games last year, the switch-hitting outfielder posted strong all-around numbers in his first taste of Single-A ball this season. 

Hartshorn slashed .273/.424/.460 with five home runs, nine doubles, one triple, 25 RBI, and four stolen bases across 39 games for the Myrtle Beach Pelicans. He also drew more walks (34) than strikeouts (27) while carrying a strong .884 OPS. 

There’s a reason why Hartshorn is being promoted after only 39 Single-A games. He showcased both his solid contact skills and power in his 177 plate appearances, and his discipline at the plate was also on display. The young hitter had an incredible 19.2% walk rate with the Pelicans. 

Then, there’s McGwire, who might be the most underrated prospect in the Cubs organization right now. The 6-foot-4 right-hander is not listed as a top-30 prospect in Chicago’s farm system on MLB Pipeline or as a top-34 prospect on FanGraphs. 

McGwire missed the entire 2025 season due to an injury, but he is off to a fantastic start on the mound this year. The 22-year-old had a 2.40 ERA, a 1.067 WHIP, and 45 strikeouts across 30 innings at Single-A before his promotion. 

McGwire's numbers to start the year have been a pleasant surprise. This is the same pitcher who posted a 5.71 ERA and a 15.9% strikeout rate across 15 appearances (eight starts) with Myrtle Beach during the 2024 season. 

The biggest difference for McGwire has been the strikeout numbers. He has a 36.6% strikeout rate in 10 appearances (five starts) this year and has struck out at least seven batters in three of his last four outings. In his most recent start, the young right-hander struck out seven batters across four innings. 

McGwire was selected in the eighth round of the 2022 MLB Draft and is the son of former All-Star first baseman Mark McGwire. The 22-year-old could quickly rise up prospect rankings with a devastating splitter. 

Something to keep in mind with McGwire is that he could be Rule 5 eligible this upcoming offseason. So, his ascension through the minors this season will be interesting. The Cubs will have to add him to the 40-man roster after this year or risk losing him in the Rule 5 Draft in December.