3 Mariners prospects who've made their case for promotions, 3 who must do more

It was around this time last year that the Seattle Mariners started moving pieces around in their minor league system. Most notably, Lazaro Montes and Michael Arroyo got bumped to Double-A Arkansas after laying waste to High-A pitching with the Everett AquaSox.

Granted, the timing doesn't necessarily mean we're about to see a rush of promotions now in 2026. The decision-making process is more complicated than that, as simply putting in time at various levels of the minors is hardly the only thing prospects must do to work their way toward the majors.

So, let's look at three prominent Mariners prospects who are ready for their next challenge, and three who need more time where they are.

These 3 Mariners prospects are ready for the next level of the minor leagues

LHP Kade Anderson, Double-A Arkansas

Might as well begin with the obvious one. Though it still hasn't been a full year since the Mariners chose him with the No. 3 pick in the 2025 draft, Anderson has needed just 12 starts to show he's too good for Double-A. He's riding a 27.2-inning scoreless streak, and he has a 1.02 ERA, 90 strikeouts and eight walks over 61.2 total innings.

The Mariners have sent several strong hints that they see the 21-year-old lefty as a potential major league contributor in 2026. But he'll surely need at least a start or two for Triple-A Tacoma before that day comes, and it's not exactly getting easier to deny him that chance.

RF Lazaro Montes, Double-A Arkansas

At the time the Mariners bumped Montes to Double-A in 2025, he had a .959 OPS and 18 home runs in 67 games with Everett. The 21-year-old was promptly humbled by Double-A pitching, posting a .752 OPS down the stretch of 2025 and a .786 OPS in April of this year.

Well, he's been unstoppable since then, with a .901 OPS and 18 homers to show for his last 45 games. That's not the only reason to get him to Tacoma, as he also needs to be spared from further harm inflicted by Dickey-Stephens Park. He has a .631 OPS there this year, compared to a 1.092 OPS in road games.

SS Felnin Celesten, High-A Everett

This is where we might be pushing it a little. Celesten is coming off an injury-marred 2025 season, and he only has a total of 74 games at the High-A level. Montes, Arroyo and Colt Emerson all played over 100 there before they got promoted to Double-A.

Then again, Celesten is healthy and looking the part amid a surge since May 1, in which he's slashed .316/.413/.511 with 10 homers and 16 stolen bases. As the 20-year-old is also an ace defender, you could make the case that he's doing Emerson's High-A act even better than Emerson himself did it.

These 3 Mariners prospects have more to prove before they get promoted

RHP Ryan Sloan, Double-A Arkansas

Like Félix Hernández two decades ago, Sloan is considered by some to be the best pitching prospect in baseball. And on paper, a 20-year-old with three plus pitches and standout command does sound too good to be true.

Despite some bright spots here and there, though, Sloan has a 4.35 ERA and has given up 53 hits (including seven home runs) over 51.2 innings this season. And he isn't trending well, with the month of June seeing him give up a .923 OPS fueled by 10 extra-base hits in 60 at-bats. His major league debut may yet come this year, but he needs to build a better runway first.

LF/2B Michael Arroyo, Double-A Arkansas

Now that Emerson is in the majors, Arroyo has a case as the best pure hitter in the Mariners' minor league system. He has a .400 OBP for his career, and he did Colombia proud in the World Baseball Classic by posting a .500 OBP in four games back in March.

Unlike Montes, however, Arroyo is still solving the Double-A puzzle. Though he has made progress with an .839 OPS this month, he still has a modest .732 OPS to show for 110 games with Arkansas. Though the Mariners are unlikely to end the experiment, one wonders if shifting back and forth between left field and second base is holding him back.

CF Jonny Farmelo, High-A Everett

Finally, a feel-good season for Farmelo. He tore his ACL in 2024 and continued to get bit by injuries in 2025, resulting in him rolling into 2026 with just 75 minor league games on his record since going to the Mariners at No. 30 overall in the 2023 draft. Against that backdrop, a 65-game sample with an .847 OPS, 10 homers and 20 stolen bases is a heck of a shining light.

Even so, this is a case of a spectacular June (1.081 OPS, 6 HR) covering up how April and May were kind of mid. Farmelo also has a 26.1 K%, which is higher than you want for a 21-year-old at the High-A level. Contrary to Celesten, the Mariners should absolutely want to get him over 100 games with Everett before they hand him a ticket to Arkansas.

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