Every year, countless individual prospects improve their standing in the eyes of talent evaluators. Sometimes they've made substantive adjustments, others they've just progressed more quickly than anticipated, and sometimes these players are just more talented than they were initially determined to be. The following is a list of players that fit somewhere on this landscape and who are now in position, via some combination of their own talent and their parent club's roster, to reach the big leagues next year.
I have several swing changers on this list, as well as players who have bounced back from injury, players who have matured at a rate beyond the norm and some players who simply exceeded expectations. If you're curious about seemingly obvious omissions such as Vladimir Guerrero Jr. and Eloy Jimenez -- who are almost certain to debut next year as their parent clubs' desire to manipulate service time prevents it this season -- know that those players were viewed as elite entering the season and that I don't consider them 'breakout' prospects.
American League
Dean Kremer, RHP, Baltimore Orioles: Acquired as part of the return for Manny Machado, Kremer's artificially high ERA from 2017 regressed to the mean this year. He didn't break out so much as he's just no longer overlooked. There's some risk that he ends up in a relief role, but if a complementary changeup develops for Kremer, he'll pitch in Baltimore's rotation for a long time.