The Orioles’ roster went through significant transformation this winter, and then even more this spring.

Now at the start of their third season in a long-term rebuilding project, the O's enter 2021 with most of their rotation, the entire infield and good chunks of their bullpen looking different than a year ago. More turnover appears on the way, with an exciting second wave of prospects expected to arrive this summer.

For now, the Orioles head north with a 26-man group that includes five rookies and the return of their top slugger after a year battling cancer. The roster’s strength is its outfield mix and its priority is pitching depth, with the O’s opting to open the season with a 14-man staff and just three bench players.

“We had a lot of decisions to make in camp this year,” manager Brandon Hyde said. “We tried to build up as many guys as possible, and brought in as many starters as we possibly could, because we know this season is going to be different. We’re going to need innings on the mound and a lot of different guys to pitch for us.”

That makes this roster, of course, subject to change throughout the year. It will often. Here is the Orioles’ official 2021 Opening Day roster:

Catchers (2): Pedro Severino, Chance Sisco
Severino looked like a trade candidate this winter with top prospect Adley Rutschman on the way, but nothing materialized on that front. Rutschman got a long look in camp, but he isn’t a candidate to debut until at least late 2021, and probably later. That leaves Severino and Sisco returning behind the plate in more or less a platoon situation, with Sisco a candidate to get some at-bats at designated hitter as well.

First base (1): Trey Mancini
The emergence of Anthony Santander in right field has the Orioles planning on slotting Mancini back in at his natural position of first base more regularly this season, his first since missing all of 2020 recovering from Stage 3 colon cancer. Chris Davis remains rooted to the roster by virtue of his contract, which runs through ’22, but he will begin the year on the 60-day injured list nursing a lower back strain. Ryan Mountcastle, Maikel Franco and Pat Valaika could also see time at first base when Mancini serves as DH.

Second base (1): Pat Valaika
All spring, the second-base job looked destined for Yolmer Sánchez, the 2019 American League Gold Glove Award winner at the position. But the Orioles designated Sánchez for assignment during the final week of camp to clear space for pitching depth, thrusting utility men Valaika and Ramón Urías into the role. Valaika probably starts most nights until a more permanent replacement is found after hitting .277 with eight homers in 52 games in '20.

Third base (2): Maikel Franco, Rio Ruiz
Signed to a one-year, $800,000 deal with incentives on March 16, Franco likely pushes Ruiz out of a starting job. A former top prospect with the Phillies, Franco is still just 28, and hit .278 with eight homers and a .778 OPS in 60 games last season for the Royals. Ruiz was inconsistent, starting basically every day at the hot corner over the past two seasons, hitting .229 with 21 homers and a .692 OPS over that span. He’ll head north as the lone left-handed option on Hyde’s three-man bench.

Shortstop (1): Freddy Galvis
A durable nine-year veteran, Galvis signed a one-year, $1.5 million deal in January to replace José Iglesias as the O’s everyday shortstop. Barring injury, that’s what he’ll be.

Outfield (4): Ryan Mountcastle, Cedric Mullins, Anthony Santander, Austin Hays
This group is the strength of the team; nowhere on the field has progress been more evident during the Orioles' rebuild than in the outfield.

Mountcastle, Mullins and Santander will start most days from left to right, while likely occupying three of the top four spots in the O’s order. Mountcastle is an AL Rookie of the Year Award favorite after his impressive 2020 debut, Mullins rebuilt his value as a table setter and impact defender in center and Santander broke out enough to see his name pop up in trade rumors this winter. Hays had a terrific spring and brings enough flexibility to profile as a fourth outfielder in name only; he’ll play more or less every day, siphoning at-bats from Mullins against left-handed pitching, at DH and replacing Mountcastle on defense late in games.

(We aren’t listing a DH here because Hyde is planning to rotate several players through that spot, including the aforementioned Mancini, Hays, Franco and Ruiz. DJ Stewart looked like a candidate to gobble up at-bats here, but he missed most of camp with a left hamstring strain and will begin the season on the injured list.)

Utility (1): Ramón Urías
The decision to jettison Sánchez and bring 14 pitchers north leaves the Orioles with a three-man bench, and makes infield versatility extremely valuable. Urías brings it in droves, capable of playing anywhere on the infield and showing some punch at the plate, albeit in a small sample. In truth, he might start at second as much as Valaika does. But both are super utility players by trade, and both beat out Richie Martin (late start due to a broken hamate bone) and Stevie Wilkerson for roster spots this spring.

Starting pitchers (5): John Means, Matt Harvey, Bruce Zimmermann, Jorge López, Dean Kremer
The Orioles took fliers on big-name reclamation projects Harvey and Félix Hernández this winter, in part to ease workload concerns on Kremer and other rookies who enjoyed impressive 2020 debuts but won’t be pushed innings-wise in '21. Harvey made the team as the No. 2 starter, but Hernández didn’t, and poor performance from No. 11 prospect Keegan Akin opened the door for Zimmermann and López to swoop in and claim rotation jobs.

This alignment, though, is tenuous; Baltimore is still going to use more than five starters this year, making depth options like Akin, Wade LeBlanc and Adam Plutko important figures. It will be important not only for Means to regain his 2019 All-Star form, but to provide length whenever he takes the mound.

Relievers (9): Tanner Scott, César Valdez, Paul Fry, Dillon Tate, Cole Sulser, Tyler Wells, Mac Sceroler, Wade LeBlanc, Adam Plutko
The shortened 2020 season was good for the Orioles' bullpen, which improved from one of baseball’s worst units the year before to one of its better groups. Was part of that due to sample size? Perhaps. But another part was the steps forward taken by hard-throwing lefty Scott, former top prospect Tate and setup man Fry, as well as the finding of Valdez. Even without Hunter Harvey healthy, this is a unit that could surprise some people, particularly on the back end.

It’s also certain to evolve from a personnel standpoint throughout the year, as the Orioles look to fill innings with swingmen, bullpen days and other creative solutions. Hence the four long-man types heading north for Opening Day; Valdez, Sceroler, LeBlanc and Plutko could all start if called upon or provide length in bulk-inning roles. Sceroler and Wells are Rule 5 Draft picks who made the team with impressive springs, Scott is the top candidate for save opportunities and Plutko was acquired in a trade from the Indians last week. Right-hander Shawn Armstrong, a mainstay in recent years, will reportedly begin the season on the paternity list.