The amount breaks the previous arbitration record of $26 million, set by Colorado Rockies star third baseman Nolan Arenado last off-season. Arenado later secured an eight-year, $260 million contract with the Rockies.
The Red Sox also announced one-year deals with outfielder Jackie Bradley Jr. ($11 million) and relief pitchers Brandon Workman ($3.5 million), Matt Barnes ($3.1 million) and Heath Hembree ($1.6125 million).
Betts, who will become a free agent after the 2020 campaign, recorded a .295 batting average with 29 home runs and 80 RBIs last season. He also led the American League with 135 runs scored.
Betts, 27, avoided arbitration in 2019 by settling with the Red Sox for $20 million. Boston selected the versatile outfielder in the fifth round of the 2011 MLB Draft.