On a franchise-shaping Monday in Boston, the Celtics locked up two of their most important players for the foreseeable future.

Weeks after winning their 18th NBA championship, the Celtics agreed to terms on big-money contract extensions for starters Jayson Tatum and Derrick White.

White’s new deal is worth $125.9 million over four years, according to multiple reports. Tatum’s reportedly is a gargantuan five-year, $315 million contract that makes him the highest-paid player in league history.

Tatum’s payday breaks the previous record set by Tatum’s Celtics co-star, Jaylen Brown, when he signed for five years and $304 million last July.

Sandwiched between Monday’s two contract reports was an even more seismic announcement: Wyc Grousbeck’s revelation that he is putting the Celtics up for sale and expects to have a new majority owner in place by early 2025 (with Grousbeck planning to stay on as team governor until 2028).

That new owner will inherit a roster nearly identical to the one that won the NBA title last month, with all five starters and the top four reserves all under contract for the upcoming season.

Tatum had one year remaining on his previous contract, plus a player option for 2025-26, but signing him to an extension seemed inevitable as soon as he became supermax eligible this offseason.

The five-time All-Star made the All-NBA first team in each of the last three seasons, and Boston’s long-awaiting championship solidified his status as a truly elite player. Tatum drew criticism for his shooting struggles during the 2024 playoffs, but he led all Celtics players in points, rebounds and assists in both the NBA Finals and the postseason as a whole.

“Jayson makes greatness look easy,” head coach Joe Mazzulla said after Tatum dished out 12 assists in Game 2 of the Finals. “He does it in a lot of different ways. He does it on defense, he does it on rebounding, he does it on passing, he does it on screening. He’s a tremendous player, and (it’s) not hard to coach him. When he has the ability to affect the game in different ways, we’re a different team.”

Tatum’s 26.9 points per game during the regular season ranked eighth in the NBA, and he finished sixth in MVP voting. He’s missed fewer than 10 games in each of the last three seasons and, at just 26 years old, still is squarely in his athletic prime.

White was set to enter the final year of his previous deal, meaning he would have hit unrestricted free agency next offseason. Waiting and testing the market might have landed him a more lucrative payday, but the do-it-all guard now gets long-term security with the franchise and city he’s said he adores.

News of the extension broke one day before White’s 30th birthday.

Acquired from San Antonio at the 2022 trade deadline, White enjoyed a career year in 2023-24, starting 73 games and averaging 15.2 points, 4.2 rebounds, 5.2 assists, 1.0 steals and 1.2 blocks per contest. He led all NBA guards in blocked shots; posted career highs in rebounding, 3-point shooting percentage and free-throw percentage; and posted the second-best plus-minus in the league (8.5), trailing only three-time Most Valuable Player Nikola Jokic (8.6).

White formed one half of the NBA’s best defensive backcourt with Jrue Holiday, who joined him on the All-Defensive second team, and made key contributions on both ends of the floor throughout Boston’s playoff run.

On top of his defensive highlights — including his game-saving chasedown block in Game 2 of the NBA Finals against Dallas — he shot 40.4% from deep in the postseason and ranked fifth among all playoff participants in made threes per game. White also played through an unfortunate dental injury in the Celtics’ championship clincher, cracking one tooth and dislodging two others while diving on the floor for a loose ball.

“(It’s) such a blessing to be a part of this roster,” White said after the NBA Finals concluded. “They just drive me in so many different ways, from top to bottom. I’m just so thankful and grateful for each and every one of them. They made me a better player and made me a better person. The city of Boston, everything, has just been amazing for me.”

Each time he was asked about his contract status, the soft-spoken White reiterated that he loves playing for the Celtics.

“I’ve always said I love it here, and that has never changed,” he told the Herald last week.

Celtics president of basketball operations Brad Stevens, who swung the trade that brought White to Boston, also repeatedly stressed that he wanted to keep him around.

“Derrick has had an amazing year,” Stevens said in April. “Derrick is a huge, huge part of our team, and we want him around for as long as we can keep him.”

White reportedly is a candidate to join Tatum and Holiday on the U.S. Olympic team as an injury replacement. He said he would gladly play if invited.

Keeping their championship core intact has been a clear priority for the Celtics this offseason. Before extending White and Tatum, they took steps to retain several of their top bench options, picking up the team option in Sam Hauser’s contract and re-signing backup centers Luke Kornet and Neemias Queta. Boston also selected Creighton guard Baylor Scheierman and Gonzaga forward Anton Watson in the first and second round of last week’s 2024 NBA Draft, respectively.