Danny Ainge is stepping down as the Boston Celtics' president of basketball operations and the franchise is elevating coach Brad Stevens to run basketball operations, sources told ESPN's Adrian Wojnarowski.

The Celtics will start a search to hire a head coach to replace Stevens, sources said.

Celtics staff were informed of the changes Wednesday morning, and a formal announcement is expected today, sources said.

Ainge has been contemplating leaving the job for several months and had been talking about possible succession plans with ownership, according to sources.

Ainge also moved from head coaching in the NBA to the front office, with Phoenix.

Stevens has been described as worn down with coaching since The Bubble, and he welcomed the chance to make the transition to the front office, sources said. Stevens will help lead the search for his successor as head coach.

The move comes a day after Boston's disappointing season came to an end in a loss to the Brooklyn Nets in Game 5 of their first-round playoff series in Brooklyn.

Ainge, 62, was the architect of Boston's last title team, the 2008 team featuring Paul Pierce, Kevin Garnett and Ray Allen, and is the third-longest-tenured active lead executive of any NBA franchise, trailing only longtime nemesis Pat Riley with the Miami Heat (1995) and Gregg Popovich with the San Antonio Spurs (1996).

The Celtics are headed into what is a pivotal offseason for the franchise after Boston finished seventh in the Eastern Conference on the heels of making it to the conference finals three of the past four years. After years of having surplus draft picks and the opportunity to make moves in free agency, the Celtics find themselves without either this offseason.

Kemba Walker, the team's highest-paid player, has two years and $73 million remaining on his deal, and he is coming off a season that saw him miss 29 games -- plus Boston's final two playoff games -- with knee issues. Marcus Smart, the team's emotional leader, is entering the final year of his contract and is extension-eligible. And Evan Fournier, whom Boston acquired at the trade deadline after using a significant portion of the trade exception created when Gordon Hayward departed in free agency last offseason, will be an unrestricted free agent.

Ainge came to Boston in 2003, in one of the first major decisions that owner Wyc Grousbeck made after buying the team the previous fall. The move came about in an unusual way, with Ainge being hired in the middle of the Celtics facing the then-New Jersey Nets during the Eastern Conference semifinals, a series Boston would go on to lose.

"I had no interest in waiting until mid-June to see if he happened to still be available," Grousbeck said at the time.

It turned out to be a decision Grousbeck wouldn't regret, as Ainge swung the deals for Garnett and Allen in the summer of 2007 that turned the Celtics into champions for the first time in over 20 years in 2008, before then sending Garnett and Pierce to the Nets for a bevy of future draft picks in 2013 -- a haul that eventually turned into the cornerstones of the current squad, Jayson Tatum and Jaylen Brown.

Across his 18 years with the Celtics, Ainge has hired only two coaches: Doc Rivers, whom he hired in 2004, after his first season in charge, before shocking the basketball world by hiring then-Butler University coach Stevens, who replaced Rivers after he went to coach the LA Clippers in 2013.

But, despite the success the Celtics have had in recent seasons, including reaching the Eastern Conference finals in 2017, '18 and '20, it has been a tumultuous run for the franchise. Ainge was criticized for moving on from Isaiah Thomas in the blockbuster deal that brought Kyrie Irving to Boston during the 2017 offseason. While no one questioned the move from a talent standpoint, Thomas had played hurt in the playoffs and helped the Celtics make the conference finals, and the move revived the old "Trader Danny" moniker Ainge was given after he'd traded another franchise favorite, Antoine Walker, more than a decade earlier.

Ironically, the other criticism Ainge had received in recent seasons was that he'd been too stingy in his willingness to make deals. Rather than offering up any of the draft picks or young players he had accumulated to get win-now talent for any of a series of stars who became available, including Paul George, Jimmy Butler, Kawhi Leonard and James Harden, Ainge chose to stand pat.

The one time Ainge did pull the trigger on such a deal was to get Irving -- and that wound up backfiring as he was injured during the 2018 playoffs before the 2019 version of the team imploded in the Eastern Conference semifinals, and Irving departed for the Nets later that summer.

Irving was just one of several players in recent seasons to depart with no immediate help coming back -- a list including Al Horford, Hayward and Marcus Morris, a talent drain that helped put Boston in the position it found itself in this season, when a top-heavy roster couldn't sustain success when injuries and bouts of COVID-19 hit. Boston limped to the seventh seed in the East before losing to the Nets with three key players -- Brown, Walker and Robert Williams -- sitting out with injuries.