Boston Celtics forward Sam Hauser -- one of the NBA's most accurate 3-point shooters -- has agreed to a four-year, $45 million contract extension, his agent Jason Glushon told ESPN on Sunday.

Hauser, who will make $2 million in the 2024-25 season, will be under contract through 2028-29 on a Celtics payroll that is set to become one of the most costly in NBA history.

Undrafted out of the University of Virginia in 2021, Hauser has been a Celtics development success story and played a significant part in the franchise's championship ascension. He shot 42.4% on 3-pointers last season, fourth best among players with 400-plus attempts, according to ESPN Stats & Information. For his career, he has shot 42.2% from 3-point range.

Besides Hauser, the Celtics have signed All-NBA forward Jayson Tatum (five years, $315 million) and guard Derrick White (four years, $125 million) on extensions this summer.

Adding Hauser's extension to the Celtics' 2025-26 payroll elevates it to a projected $225 million with an additional $210 million luxury tax penalty. The Celtics are expected to be over the league's second apron for a second consecutive year, which would make their 2032 and 2033 first-round picks untradable.

The Celtics' combined salary and luxury tax is projected to be the largest in league history. The Phoenix Suns currently have a combined $432 million bill.

Hauser, 26, made 179 catch-and-shoot 3-pointers last season, sixth most in the NBA, according to Second Spectrum.

Hauser became the third player in Celtics history to make 10 three-pointers in a game last season, joining Jaylen Brown and Marcus Smart.

ESPN's Bobby Marks contributed to this report.