Right-hander Brayan Bello and the Boston Red Sox have agreed to a six-year, $55 million contract extension, sources told ESPN, locking up the hard-throwing 24-year-old whose changeup is already one of the best in Major League Baseball.

The deal includes a seventh-year club option worth $21 million, according to sources.

The Red Sox announced the six-year agreement but did not disclose terms.

In his first full big league season last year, Bello went 12-11 with a 4.24 ERA and struck out 132 against 45 walks in 157 innings. For an organization that has struggled in recent years to develop big league starting pitching, Bello is a success story -- and he should help anchor Boston's rotation into the 2030s.

Signed for just $28,000 out of the Dominican Republic in 2017, Bello debuted in 2022 and quickly grabbed a starting role for a Red Sox team that is coming off back-to-back last-place finishes in the American League East. With a sinker that sits around 95 mph and a devastating changeup that he regularly buries on the outside corner to left-handed hitters, Bello emerged as Boston's most reliable starter last year.

Bello could get the nod as Boston's Opening Day starter, with free agent signing Lucas Giolito expected to miss the season with an elbow injury, sources said.

While Boston's farm system is littered with potential impact bats -- outfielder Roman Anthony, shortstop Marcelo Mayer and catcher Kyle Teel among them -- the organization has graduated few rotation options in recent seasons. Right-handers Wikelman Gonzalez and Luis Perales could be future rotation staples, and the Red Sox are high on right-hander David Sandlin -- acquired in a deal for reliever John Schreiber this winter -- but Boston is likelier in the short term to supplement its starting depth via free agency and trade.

For now, right-handers Nick Pivetta, Kutter Crawford, Garrett Whitlock and Tanner Houck are the front-runners to join Bello in Boston's rotation. Whitlock and Houck have bounced between relief and starting roles, and right-hander Josh Winckowski -- who was also a reliever last season -- is competing for a rotation spot as well.

Bello's emergence prompted the Red Sox to seek an extension after a slow offseason in which they signed only Giolito, reliever Liam Hendriks (out for most of the 2024 season after Tommy John surgery) and right-hander Cooper Criswell, handing out less than $50 million total following chairman Tom Werner's comments that Boston would go "full throttle" in its free agent pursuits this winter.

After whiffing on Shohei Ohtani and Yoshinobu Yamamoto, both of whom went to the Los Angeles Dodgers, the Red Sox have declined to reallocate the hundreds of millions of dollars they were willing to guarantee to both. Reigning National League Cy Young winner Blake Snell and left-hander Jordan Montgomery -- in whom the Red Sox have shown interest this offseason -- remain free agents.