Betts was named the American League's Most Valuable Player in 2018 after posting an outstanding .346/.438/.640 triple-slash line with career-high totals in both home runs (32) and stolen bases (30). He's also earned three straight All-Star selections.
The 26-year-old Tennessee native ranks second among all MLB players in WAR since the start of 2015, his first full season in the big leagues, at 28.7, per FanGraphs. Only the Los Angeles Angels' Mike Trout (35.6) is ahead of him on the list.
Betts struggled in the postseason, finishing with a mundane .623 OPS and one homer in 14 appearances, but the star-studded Red Sox still rolled to the 2018 World Series title.
"I mean, it means a lot," Betts told reporters after being named MVP. "It's definitely a special award and something that I cherish, but I think the most important thing is that we won a World Series and got to bring a trophy back to Boston."
While Friday's deal settles the right fielder's status for 2019, the focus will soon shift toward his long-term future, with 2020 being the last season of team control. He can become an unrestricted free agent ahead of the 2021 campaign without an extension in place.
It's the same offseason Trout—who's currently earning $34.1 million annually as part of his six-year, $144.5 contract with the Angels—could hit the open market.
If Trout and Betts become available the same winter, it would make the recent free-agent pursuits of outfielder Bryce Harper and shortstop Manny Machado look minuscule in comparison.
The Red Sox will likely do everything in their power to prevent that by locking up their franchise cornerstone to a massive extension over the next few years.