We know that Halo 4 is the start of a new trilogy focused on the Forerunners, but Master Chief's own role in the conflict has been given a bit more detail now. Apparently the hero has been set adrift for quite a while, and Cortana's long life is beginning to catch up with her.
"There's some fairly radical modifications to his armor" 343's Frank O'Connor told Xbox World (via CVG). "Some of those are an artistic evolution, but some are connected to the story. We just can't talk about it yet. He's been in space for a long time."
Meanwhile, Cortana will be in danger again, this time from her own expiration date. "Seven years is the lifespan for a smart AI before it enters a state called rampancy," O'Connor said. "Cortana was getting close to the end of her natural lifespan at the end of Halo 3 but she has been exposed to far more information than any other AI in existence. She's going to develop some muscle from that process but it also contributes to her rampancy - that much information makes things worse."
In general terms, these story hooks add color to the overall plot regarding the Forerunners. O'Connor says he wants this trilogy to bring back "the sense of wonder and mystery. We're definitely going back to that air of exploration, and putting in some surprises that I think people will like."
Halo 4, the first entry in the new trilogy, will hit in 2012.