"Halo 4 is the next blockbuster installment in the iconic franchise that’s shaped entertainment history and defined a decade of gaming. Set in the aftermath of Halo 3, Master Chief returns to confront his own destiny and face an ancient evil that threatens the fate of the entire universe. Halo 4 marks the start of a new trilogy that begins with its release in 2012."
- as seen on the official Halo site.
So... Halo 4!
Halo 4 is a continuation of the Halo franchise (set after being in space for a long time) and is the beginning of a new Halo trilogy named "The Reclaimer Trilogy". This new trilogy is designed to take players on a decade-long journey that involves a more in-depth look at the Forerunners along with looking at Master Chief's character and personality in greater depth.
Creative manager Josh Holmes stated at ""It plays like Halo, It sounds simple but that was really important to us." The panel refused to go on about the Story of the new trilogy however they did mention that "it will deal with the fate of John and Cortana. There's a lot of speculation about Cortana's mind state. There's a lot of relationship between those two characters. Character is something we're focusing on very strongly this time."
I've found a release date for Halo 4 (12/12/12) although i am not sure if it is reliable, but that's all we have right now so lets work with it! On the Wednesday of December 2012 i think that sales are going to shatter all gaming records due to the large amount of loyal fans following the halo franchise including myself.