The helmer added that it was the video game adaptation that got buzz for another instalment in the series going again.
"Certainly, Sony has been all over us for about two decades now, trying to get this going," Reitman told Sci Fi Wire at the Santa Barbara International Film Festival.
"We have this sort of very interesting deal in which we really control the forward progress of the movie. [Sony] did a very interesting thing. They actually hired these two writers on their own, without consulting us, and basically said, 'We're going to start."
Reitman also praised screenwriters Lee Eisenberg and Gene Stupnitsky, saying: "[They are] very good writers, fortunately, and they wrote a first draft that was pretty good, considering that they didn't really talk to us that much. And I've since then been working with them for the last four or five months, just trying to get more of the kind of spirit of the film into it."
But the filmmaker went on to caution that the project is still in its very early stages. "There seems to be a lot of enthusiasm from everybody [about the return of original stars Billy Murray, Dan Aykroyd, Harold Ramis and Sigourney Weaver].
"We'll see. It's still not a reality. There are no deals. There's no real finished script," he continued.