Baynes himself confirmed the agreement via Twitter on Sunday:
Since going undrafted out of Washington State back in 2009, the 6'10", 260-pound big man bounced around professional leagues before establishing himself in the NBA with the San Antonio Spurs. He has since played for the Detroit Pistons and the Celtics.
In his first season in Boston, Baynes averaged 6.0 points and 5.4 rebounds in 18.3 minutes per game. He worked his way into the playoff rotation, starting 12 of 19 games. He averaged 6.0 points and 6.2 rebounds while helping the under-manned Celtics come within one game of the NBA Finals.
There's more to Baynes' game than what shows up on a stat sheet, though. Celtics coach Brad Stevens recently explained to The Athletic's Jay King what makes the center valuable:
"We want them back for a number of reasons. Their energy is contagious, and it's contagious every day. I tell the story all the time about (how) Aron Baynes races people in warmups. And he just brings an infectiousness that I can't describe. And I think, like, my thoughts of this team are him and Marcus running down the court flying as everybody's supposed to be doing high knees and warming up. ...
"I'm telling you, Baynes makes everything a race. Baynes has been at the gym probably three hours before that. Like, he gets there super early, he works really hard. But he's always laughing, jovial, brings a great energy to it. I really appreciate all that about him."
Baynes has steadily seen an expanded role in recent seasons, and he has rewarded teams for taking a chance on him. Now, Boston is rewarding him for his contributions.