Los Angeles (CNN) -- The upcoming ninth season of NBC's "The Office" will be the sitcom's last, executive producer Greg Daniels said Tuesday.
Though the show's ratings are healthy -- it is NBC's highest-rated scripted series -- contracts are expiring for most of the original cast, making it "the last chance for us to go out together and to make an artistic ending," Daniels said.
All 15 of the characters from season eight will return, with the addition of Jake Lacy and Clark Duke, he said. But the contracts of most of the veterans are expiring, he said.
"They all have exciting opportunities," he said. "We couldn't count on getting that many people back for season 10."
The show could have continued by adding characters as veteran stars moved on to other projects, but "the show would be changed to such a degree that it wouldn't be the same show," he said.
The final season will "do justice to the existing characters in the most creative and explosive way," he added.
"As we head into the home stretch, we have a lot of exciting things I personally have been wanting to do since season two and the ending should be pretty cool," Daniels said.
One story arc in particular is the relationship between receptionist Pam Beesly and salesman Jim Halpert, he said. "The most loyal fans would really want to see that happen," he said.
The last season will also reveal details viewers have been guessing about, including the "documentary" that was being produced in the office.
"Basically, all questions will be answered this year," Daniels said. "We are going to see who is behind the documentary."
Knowing it is the final year, producers can do the "kind of risky things that we wouldn't normally do if we knew we were going for a long time. But we can kind of blow up things and take some chances."
The final season premieres at 9 p.m. September 20.