Multiple outlets reported the value of the deal at $10 million.
Benintendi, 25, has been Boston's Opening Day left fielder for each of the last three seasons.
He batted .266 with 13 homers, 40 doubles and 68 RBIs in 138 games last season, and is hitting .277 with 51 homers, 259 RBIs and 52 stolen bases in 471 games since making his debut in 2016.
Benintendi helped the Red Sox win the 2018 World Series against the Los Angeles Dodgers, leading all players with 15 runs scored during the postseason.
He was drafted by Boston in the first round (seventh overall) in 2015 and was runner-up to New York Yankees slugger Aaron Judge for 2017 American League Rookie of the Year.
Left-hander Eduardo Rodriguez is the only remaining Red Sox player eligible for arbitration.
--Field Level Media