The Boston Celtics are expected to offer a record five-year, $315 million supermax contract extension to their ace Jayson Tatum, according to multiple media outlets including ESPN and The Athletic.

"Once these NBA Finals are over, teams are now allowed to start negotiating contract extensions, negotiating with their own free agents," ESPN reported ahead of Game 5 of the NBA Finals on Monday. "Which means that the Celtics will soon present Jayson Tatum with the largest contract in NBA history, a five-year, $315 million extension."

Tatum, who was drafted by the Celtics with the third-overall pick in 2017, just finished the third year of his five-year, $163 million deal with the team after the 2023-24 season. He has a player option for the 2025-26 campaign.

"The Celtics and Jayson Tatum will start beginning talks on that five-year, $315 million deal, that'll happen after everyone's sobered up," The Athletic reported on Tuesday. "The whole team is in Miami right now, they're having a great time, and then the parade is going to be Friday. I would expect, at some point after that, Jayson Tatum and his agent and the Celtics get down to brass tacks."

Tatum has been an NBA All-Star selection for five straight seasons and an All-NBA First-Team nod for three consecutive seasons. He averaged 26.9 points, 8.1 rebounds and 4.9 assists per game during the 2023-24 regular season for the 64-win Celtics. Then he averaged 25 points, 9.7 rebounds and 6.3 assists per game for the team to win four postseason series 4-1, 4-1, 4-0 and 4-1 before claiming the league record 18th title.

Tatum was not named the NBA Finals Most Valuable Player, which went to his teammate Jaylen Brown. Brown signed a five-year, $304 million extension with the Celtics last year.