Boston’s Jayson Tatum, left, celebrates after the Celtics beat Dallas to win the NBA title on June 17. Tatum and the Celtics have agreed to a supermax deal worth $315 million over five seasons. Charles Krupa/Associated Press

Jayson Tatum has agreed to a five-year supermax extension with the Celtics, a league source confirmed to MassLive. The deal will kick in at the start of the 2025-26 season and be worth $315 million over five years. Tatum is expected to get a player option in year five of the deal, per a source.

Tatum joins Jaylen Brown as the only teammates in the NBA to sign supermax contracts. Tatum became eligible for the supermax after making an All-NBA team during the previous two seasons. He still has one year left on his current contract before a player option.

Tatum averaged 26.9 points, 8.1 rebounds and a career-best 3.9 assists during the regular season while shooting 47.1 percent from the field and 37.6 percent from 3-point range. He was named to All-NBA first team this season for the second straight season this year.

THE CELTICS ALSO agreed to a four-year contract extension with guard Derrick White, according to ESPN’s Adrian Wojnarowski. The deal, which is worth $125.9 million, also includes a player option.

White, acquired by the Celtics at the 2022 trade deadline from the San Antonio Spurs, averaged 15.2 points, 5.2 assists and 4.2 rebounds in the 2023-24 regular season. In the playoffs, he averaged 16.7 points, 4.1 assists and 4.3 rebounds. He has also been named to the NBA all-defensive second team each of the last two seasons.

White, 30, has one year left on his contract but was eligible for an extension this summer.

Next up on the Celtics’ to-do list is expected to be a super-max extension for Jayson Tatum. The Celtics can give Tatum a five-year, $315 million extension this summer.

On Sunday, the Celtics agreed to a multi-year contract with Neemias Queta and a one-year deal with Luke Kornet.

The Celtics turned down a team option on Queta on Saturday, which made him a restricted free agent.

Queta appeared in 28 games for the Celtics last season. He recorded career highs with 5.5 points, 4.4 rebounds and 0.8 blocks in 11.9 minutes. Boston acquired Queta last August on a two-way contract after he was waived by Sacramento. Queta played in eight games for the Maine Celtics last season, averaging 14.4 points and 8.8 rebounds per game.

Kornet played 63 games for the Celtics last season, averaging 5.3 points and 4.1 rebounds. His presence is valuable with center Kristaps Porzingis recovering from ankle surgery.

KLAY THOMPSON is moving on from the Golden State Warriors, agreeing to join the Dallas Mavericks and change franchises for the first time in his 13-year career.

Thompson is sixth on the NBA’s all-time 3-pointers made list with 2,481, behind Reggie Miller (2,560), Damian Lillard (2,607), James Harden (2,940), Ray Allen (2,973) and Thompson’s now-former “Splash Brother” with the Warriors, Stephen Curry, and his 3,747 career makes from beyond the arc.

PAUL GEORGE agreed to a four-year, $212 million free-agent contract with the Philadelphia 76ers, who also reached agreement with guard Tyrese Maxey on a five-year, $204 million extension.

George and Maxey will join center Joel Embiid in an effort to dethrone the Celtics in the East next season. George should provide a viable No. 1 scoring option when Embiid is out. The 76ers finished 31-8 in the regular season with Embiid — about a 65-win pace — and 16-27 without him.

LUKA GARZA will return to Minnesota on a two-year deal as the team made its first move since free agency opened.

Garza spent the last two seasons with the Wolves mostly on a two-way contract. But late last season when the Wolves had an open roster slot, they bumped Garza up to an NBA contract and ripped up the two-way deal. Garza will make the minimum salary on his new deal, which is just over $2.1 million for next season.

TOBIAS HARRIS, a 31-year-old forward, is heading to Detroit on a free-agent deal worth $52 million over two years.

Harris previously was with the Pistons for parts of three seasons, from 2016-18, before being traded to the Los Angeles Clippers in the Blake Griffin deal.

ISAIAH HARTENSTEIN left the New York Knicks to join the Oklahoma City Thunder after agreeing to a three-year deal worth $87 million.

Hartenstein, a center, will earn an average of $29.16 million to join Shai Gilgeous-Alexander and Chet Holmgren on a title contender out West.