The person spoke on the condition of anonymity because details have not been announced by the team.
Devers, 24, had a breakout season in 2019, when he batted .311 with 32 homers and 115 RBIs, leading the majors with 54 doubles and 359 total bases and finishing 12th in the AL MVP voting.
But last year was a setback: He hit .263 while committing 14 errors at third base -- most in the majors. The next closest was 11. Devers earned $256,481 prorated of a $692,500 salary last season.
With Devers' deal the Red Sox have come to terms will all their arbitration-eligible players this offseason. In December, Boston agreed to one-year contracts with left-hander Eduardo Rodriguez ($8.3 million), right-handers Matt Barnes ($4.5 million), Ryan Brasier ($1.25 million) and Austin Brice ($870,000), and catcher Kevin Plawecki ($1.6 million).