The duck boat parade was Jayson Tatum’s favorite part of the Celtics’ championship celebration.Kayla Bartkowski For The Boston

LAS VEGAS — About a half hour after Team USA finished practice Monday afternoon, Jayson Tatum stood on a staircase and spotted former Celtics assistant coach Charles Lee, who was recently hired to coach the Hornets.

Tatum seemed to appreciate seeing a familiar face, and he really seemed to enjoy the way he could address his ex-coach.

“What up, champ!?” Tatum boomed from the stairs before walking down to hug Lee.

The unspoken truth within Tatum’s greeting was the fact that he is now a champion, too. And the joy, satisfaction and relief that came from guiding Boston to the NBA title last month were apparent. Tatum looked like someone who has been smiling and exhaling for three weeks.

“You know, just being the topic of discussion of so many debates or whatever it is. ‘Can he lead a team? Is he a top-five player?’ ” Tatum said while standing in a quiet corner outside the gym. “There’s still a lot of things I guess they can debate, but I’ve done some things they can’t debate. I won a championship. I did it at the highest level. So having that under my belt, like, obviously there’s still conversations to be had or whatever people want to say, but they’ve always got to refer to me as an NBA champion.”

Tatum said the past few weeks have been a whirlwind. His favorite part was seeing more than one million people line the streets of Boston for the duck boat parade.

“That was like the best two hours of my life,” he said. “It’s hard to explain to somebody that wasn’t there. That was an insane atmosphere, energy. I had a hell of a time.”

He received congratulatory messages from actors, singers, and other NBA players, but the ones from people who have been with him throughout his journey were the most meaningful.

On Saturday, Tatum officially signed his five-year, $314 million extension that replaces teammate Jaylen Brown’s as the richest contract in NBA history. The deal was essentially a formality, and Tatum said he already had more than enough money to take care of his family. But he said it was significant because of what it symbolized.

“For me just to feel wanted, and they want me to be here and want me for the long haul,” Tatum said. “I’ll spend my whole career here and have got nothing but love for the fans, the city, and the organization. You know, we just won a championship and I want to try to win as many as I can.”

The quest to repeat will become Tatum’s primary focus in the near future, after the Paris Olympics as well as some much-needed downtime. But he said coach Joe Mazzulla has already begun formulating a plan for next season. Before the ink on Tatum’s massive contact had dried Saturday, Mazzulla pulled him aside and shared a few thoughts.

Coach Joe Mazzulla has already been in Jayson Tatum’s ear with ideas for next season.Danielle Parhizkaran/Globe Staff

“Joe was already trying to draw up [expletive] for next season,” Tatum said, smiling. “I was like, ‘Joe, [expletive] that. We just won the championship, like, enjoy it and relax. We’re not worried about any sets that you’re trying to put in right now.’ We had a good laugh about it, because he’s just so driven, which we all are, but it’s like, man, we worked so hard for this, we’ve got to enjoy it.”

Although Tatum is not quite ready to start thinking about next year, he is comforted by the fact that the Celtics will return their top nine rotation players from the title team. Free agents such as Luke Kornet and Xavier Tillman probably could have received more lucrative deals elsewhere, but they chose to remain in Boston to chase another championship.

“The camaraderie that we had, we were such a close-knit team, and we all got along really, really well,” Tatum said. “And I’m looking forward to it. I didn’t really want any changes. I thought we had a really, really good team on all fronts, as long as we stay healthy.”

The only curveball of the offseason arrived last week, when the Celtics announced that majority owner Wyc Grousbeck and his family were putting the team up for sale for estate planning purposes. Tatum is the face of the franchise, but said the news came as a surprise to him, too.

“I didn’t hear anything about that prior, and we just won a championship and thought everything was great,” he said. “But people have decisions they have to make for what’s best for them and their family and as a man you’ve got to respect that. I think they’ve done a great job of reassuring all of us that the day-to-day things won’t change, and our culture will be the same.”