Boston will also send the No. 16 overall draft pick and a 2025 second-rounder to the Thunder and receive 7-footer Moses Brown and a 2023 second-round pick in return.
Oklahoma City now holds 19 first-round draft picks over the next seven years.
Horford returns to Boston and gives the Celtics the frontcourt presence they’ve lacked since he left two seasons ago. The 6-foot-9 was forward was a member of the NBA All-Defensive team with the Celtics in 2017-18 while also posting the best assist numbers of his career.
Stevens coached Horford for three seasons and says he played a “critical role” while in Boston.
“His ability to elevate teammates with his experience and leadership make for a great addition,” Stevens said. “We also want to welcome Moses to Boston. He is a promising young player.”
Walker joins a team that finished with the second-worst record in the West last season but showed potential with Shai Gilgeous-Alexander, who led the Thunder with 23.7 points per game, and Lu Dort, who averaged 14 points and was one of the league’s best defensive guards.
Walker, 31, is guaranteed more than $73 million over the next two seasons. But after helping the Celtics reach the Eastern Conference finals in the NBA bubble last season the four-time All-Star he was limited by knee injuries to 43 games in 2021; he missed the last two games of the first-round playoff loss to the Brooklyn Nets.
Walker’s departure means Boston will rely more heavily on All-Stars Jayson Tatum and Jaylen Brown for scoring. Without further moves, it would also leave Marcus Smart and Payton Pritchard as the team’s main options at point guard.
But swapping his salary for Horford’s will save the Celtics $9 million.
“Kemba is a true professional and a great teammate and player,” Stevens said. “I want to thank him for his tremendous impact, and the positive contribution he’s made both to the Celtics and the city of Boston.”
After playing his first nine seasons in Atlanta, Horford signed with Boston as a free agent in 2016 and led the team to the conference finals in his first two seasons. But he opted out after three seasons to go to Philadelphia, then the 76ers flipped him to the Thunder after one year.
Horford, 35, averaged 14.2 points and 6.7 rebounds this season, but he played just 23 games before Oklahoma City shut him down in late March to take a look at younger players — including Brown.
“Thank you to … the entire Thunder organization for their professionalism during my time in Oklahoma City,” Horford tweeted. “While it was short, it was first class all the way and me and my family are extremely thankful and appreciative.”
Brown, 21, was a first-team All-G-League selection this season, and the Thunder saw enough to call him up and award him a multiyear deal. The 7-footer averaged 8.6 points and 8.9 rebounds and tied a team record with 23 rebounds against the Celtics this season.
“As soon as he got his opportunity, he really embraced it,” Horford said during the team’s exit interviews. “He took it by storm. Playing in this league is not easy, night in and night out to have to prepare, everything that it takes, and I felt like he was up for the challenge.”