Carlsson, the No. 2 pick in the 2023 NHL Draft, had 55 points (12 goals, 17 assists) in 55 games as a rookie. His 12 goals tied Stanislav Chistov's Ducks record set in 2002-03 for most by a teenager. He scored his first NHL hat trick in a 6-3 loss to the Philadelphia Flyers at Honda Center on Nov. 10, 2023. That made him the youngest player in Ducks history (18 years, 319 days) to score two goals in a game, and the 19th in League history to get a hat trick before his 19th birthday and third Ducks rookie with three goals in one game (Bobby Ryan, Sam Steel).

Carlsson signed his entry-level contract July 12, 2023, after he was named the Swedish Junior Hockey Player of the Year. His 15 assists and 25 points in 44 games for Orebro earned him player of the year honors and were the most by a junior player in the Swedish Hockey League. Those 25 points were fifth-most by a draft-eligible player in the SHL, trailing only Daniel Sedin (42 points in 1998-99), Henrik Sedin (34 points in 1998-99), Elias Lindholm (30 points in 2012-13) and Nicklas Backstrom (26 points in 2005-06). Carlsson led SHL players 20 and under in points per game (.57) and ranked second in goals, and third in points and assists. His eight playoff assists tied him for the most by a draft eligible player (also Daniel and Henrik Sedin), and his nine points trailed only Daniel Sedin (12) and Henrik Sedin (10).

Carlsson was named to Sweden's roster for the 4 Nations Face-Off and to Team Sweden for the Olympic Winter Games Milano Cortina 2026, but replaced on the Olympic roster by Minnesota Wild forward Marcus Johansson because of an injury. The Karlstad native was the youngest player to score for his country against Austria at the 2023 IIHF World Championship. He had six points (three goals, three assists) at the 2023 IIHF World Junior Championship, third among Sweden skaters in points and goals as one of two underage forwards. He won gold at the 2022 IIHF Under-18 World Championship and bronze at the 2021 Hlinka Gretzky Cup.