Until MLB announced two updates on the final day of the regular season, its rookie qualifications had remained unchanged since 1971.

For the previous 49 seasons, a player was rookie-eligible as long as he had not exceeded 130 at-bats, 50 innings or 45 days of active pre-September service time in the Majors. September service time had been excluded because rosters swelled from 25 to 40 in the final month of the season.

But with no roster expansion this year, MLB decided that September service time this year would count toward the 45-day limit. Additionally, the 2020 Rookie of the Year Award winners in each league will be ineligible to repeat as winners next season even if they otherwise qualify as rookies.

The service-time change had an immediate affect on MLB Pipeline's prospects lists, which use the same criteria used to determine rookies. Four Top 100 Prospects (Angels outfielder Jo Adell, Diamondbacks catcher Daulton Varsho, Dodgers right-hander Brusdar Graterol, Mets shortstop Andrés Giménez) suddenly graduated, as did 32 additional players on organization Top 30 Prospects lists.

Twenty-seven members of the updated Top 100 Prospects list remain eligible for the 2021 Rookie of the Year Awards (unless they win in '20) while having already accrued big league service time. We list them all below, beginning with our five top picks in each league to win the hardware next year. Note that this does not include prospects who are expected to make their Major League debuts next year.

American League
1. Ryan Mountcastle, OF/1B, Orioles (No. 90)
After winning the Triple-A International League MVP award in 2019, Mountcastle batted .333/.386/.492 with five homers in 35 games with Baltimore. He also showed more plate discipline than he had in the Minors and looked like a bat that Baltimore can build around.

2. Triston McKenzie, RHP, Indians (No. 97)
McKenzie's prospect status took a hit when he missed two months in 2018 (forearm soreness) and all of last season (upper-back strain), but he bounced back this year to post a 3.24 ERA with a .179 opponent average and a 42/9 K/BB ratio in 33 1/3 innings with Cleveland. His solid stuff plays up thanks to his advanced feel for pitching.

3. Bobby Dalbec, 1B/3B, Red Sox (No. 100)
Dalbec is the rookie most likely to go Pete Alonso in 2021. After slugging 59 homers in the Minors in 2018-19, he went deep eight times in 80 at-bats with Boston (albeit with 39 strikeouts). He comes with swing-and-miss concerns, but he draws walks and plays a quality third base.

4. Nick Madrigal, 2B, White Sox (No. 36)
Madrigal has the highest 2021 floor of all these rookies after hitting .340 with just seven strikeouts in 109 plate appearances with Chicago while also providing sound defense. There's still some question about his ceiling, however, because he had just four walks and three extra-base hits (all doubles), leading to a .745 OPS.

5. Dane Dunning, RHP, White Sox (No. 98)
Why Dunning, who hadn't pitched since June 2018 because of an elbow injury and Tommy John surgery, over more highly touted pitching prospects such as Casey Mize (Tigers) and Nate Pearson (Blue Jays)? Dunning adapted to the big leagues more easily (3.97 ERA, .197 opponents' batting average, 35/13 K/BB ratio in 34 innings) and is poised for more initial success on a better team.

National League
1. Ke'Bryan Hayes, 3B, Pirates (No. 37)
Though Hayes played just 24 games in Pittsburgh, both Baseball Reference (1.8) and Fangraphs (1.6) had him topping all NL rookies in WAR. The son of longtime big leaguer Charlie Hayes displayed more power than he had in the Minors while batting .376/.442/.682 with five homers and played his usual stellar defense at the hot corner.

2. Ian Anderson, RHP, Braves (No. 34)
Atlanta won the NL East despite several holes springing up in its rotation, one of which was plugged by Anderson, who logged a 1.95 ERA, .172 opponent average and 41 strikeouts in 32 1/3 innings. Big leaguers have yet to solve his changeup, though he'll need to continue to refine his control.

3. Sixto Sanchez, RHP, Marlins (No. 19)
Miami's prize from the J.T. Realmuto trade with the Phillies in February 2019, Sanchez helped the Marlins end a 17-year playoff drought. Relying heavily on his filthy changeup, he allowed just six runs in his first five starts before finishing with a 3.46 ERA and a 33/11 K/BB ratio in 39 innings.

4. Dylan Carlson, OF, Cardinals (No. 14)
Carlson struggled in his first three weeks with St. Louis (.162/.215/.243), then went back to the alternate site for two weeks and looked like a different hitter in the final 10 days (.278/.325/.611, including a crucial homer off Corbin Burnes). He could hit 20 or more homers next season if he recaptures the plate discipline he exhibited in the Minors.

5. Joey Bart, C, Giants (No. 11)
Bart played just 22 games in the upper Minors (all in Double-A) before getting summoned to San Francisco this summer, which contributed to his .233/.288/.320 batting line with a 41/3 K/BB ratio in 111 plate appearances. The Giants nevertheless performed significantly better when he started behind the plate (15-13, .536) than when he didn't (14-18, .438) and he should grow offensively next year while sharing catching duties with Buster Posey.

Other Top 100 candidates
Casey Mize, RHP, Tigers (No. 5)
Nate Pearson, RHP, Blue Jays (No. 6)
Cristian Pache, OF, Braves (No. 10)
Brendan McKay, LHP/DH (No. 12)
Michael Kopech, RHP, White Sox (No. 18)
Luis Patiño, RHP, Padres (No. 23)
Spencer Howard, RHP, Phillies (No. 28)
Tarik Skubal, LHP, Tigers (No. 42)
A.J. Puk, LHP, Athletics (No. 53)
Jazz Chisholm, 2B/SS, Marlins (No. 61)
Brailyn Marquez, LHP, Cubs (No. 63)
Keibert Ruiz, C, Dodgers (No. 68)
Sam Huff, C, Rangers (No. 69)
Jesús Sánchez, OF, Marlins (No. 76)
Clarke Schmidt, RHP, Yankees (No. 83)
Deivi García, RHP, Yankees (No. 87)
Garrett Crochet, LHP, White Sox (No. 89)