During the fall of 2003, Kaun committed to the University of Kansas. He also received offers from Duke and Michigan State. During his freshman season with the Kansas Jayhawks, he played in 27 games, starting twice. In his sophomore season he helped the Jayhawks to an 80–68 win against the Texas Longhorns, which made the Jayhawks the 2006 Big 12 Conference champions. During his senior year, he was the starting center for the Jayhawks and with them he won the 2008 NCAA Championship. He graduated with a degree in computer science and was selected to the Academic All Big 12 Basketball Team three times, in 2006, 2007, and 2008.
Professional career
CSKA Moscow (2008–2015)
Kaun was drafted 56th overall in the 2008 NBA Draft by the Seattle SuperSonics. He was the final draft pick in Sonics history, before the franchise moved to Oklahoma City. His NBA draft rights were then traded to the Cleveland Cavaliers for cash considerations. He signed a three-year contract worth €2,700,000 with the Russian team CSKA Moscow in 2008. On May 23, 2012, Kaun re-signed his contract with CSKA, staying three more seasons with the team. In the 2014–15 season, CSKA Moscow has managed to advance to the Euroleague Final Four for fourth straight season, after eliminating Panathinaikos for the second straight season in the quarter-final series, 3–1. However, in the semifinal game, despite being dubbed by media as an absolute favorite to advance, once again lost to Olympiacos. The final score was 70–68, after an Olympiacos comeback in 4th quarter, led by Vassilis Spanoulis. CSKA Moscow eventually won the third place after defeating Fenerbahçe with 86–80. In his "contract year", Kaun had the best season since coming in the club, starting in all 30 games played in the Euroleague and averaging career-high 9.9 points and 4.5 rebounds on 69.1% shooting from the field. After winning his fifth VTB United League championship with CSKA, there were some reports that Kaun had retired from professional basketball. A day later, Kaun denied these reports, adding that he is, however, done playing basketball in Europe.
Cleveland Cavaliers (2015–2016)
On September 9, 2015, Kaun signed with the Cleveland Cavaliers. He made his debut for the Cavaliers on October 28, recording one rebound, one assist, one steal and one block in a 106–76 win over the Memphis Grizzlies. Over the first half of the 2015–16 season, Kaun appeared in just nine games for the Cavaliers, scoring a season-high four points on two occasions. On April 11, 2016, Kaun was assigned to the Canton Charge, the Cavaliers' D-League affiliate, for a day of training. He was reassigned to Canton the next day to help the team in Game 1 of the D-League Eastern Conference Finals against the Sioux Falls Skyforce. The next day, he was recalled by the Cavaliers. Kaun did not play a single game for the Cavaliers during their playoff run, a run that ended with the Cavaliers defeating the Golden State Warriors 4–3 in the 2016 NBA Finals to win the championship. Kaun and his teammate, Timofey Mozgov, became the first Russians to win an NBA championship. On July 15, 2016, Kaun was traded, along with cash considerations, to the Philadelphia 76ers in exchange for the rights to Chukwudiebere Maduabum. He was waived by the 76ers on July 17, and six days later, he announced his retirement from professional basketball.
