What's the Situation with the "Maximum Ride" Series?

I've heard he's doing 12 books...so yay! I think he did the 4th one as a filler...so yeah. But I can't wait 'till there's more because I'm hooked on this series! But I really do think that he's doing more because at the end he really left you hanging...so yeah. (I say that a lot...sorry)