We have been teased with the idea and there's been alot of talk by the cast saying it is it isn't but now Hey Now!, Jeffrey Tambor has said the film is on, speaking to EWhe said:
After months of speculation, I think we have finally figured out for sure that we are indeed doing an Arrested Development movie. I am very excited about that. I love that cast and crew and I felt like we had more to say.
He does not mention what stage they are at production wise but its good to hear that it is finally a reality, now the countdown begins.