The Twilight: New Moon filmmaker, who produced the comedy series with his brother Paul, is serving as an executive producer on the latest movie.
Speaking to Digital Spy, Weitz admitted that the original cast - including Jason Biggs, Chris Klein and Alyson Hannigan - are experiencing a sense of nostalgia getting back together a decade after the original.
"All I've been able to do is see a few dailies from American Reunion, I think it's going to be really good actually," Weitz said.
"From what I hear people are having a great time on set, which is excellent because [it's] 10 year later, or more [from American Pie].
"I think that the actors have a sense of real nostalgia for the first film, which broke them the first time. It's really sweet to see them back together again."
Weitz's latest movie A Better Life opens in UK cinemas on Friday.
> Twilight: New Moon director Chris Weitz talks A Better Life
Watch Chris Weitz discuss American Reunion with Digital Spy below: