Announcing Halo 4 at E3 last week, Microsoft called the fourth game in the series "the dawn of a new trilogy for Xbox 360", but that won't necessarily be the case.
Halo 4 is definitely coming to Xbox 360 in 2012, but asked whether the whole trilogy will launch on Microsoft's current console, MS Games Studios VP Phil Spencer told IGN: "No announcement on that yet."
He added of the Halo 4 game engine: "We started with the code base from Halo, so it's not something we had to re-roll from the beginning... The technology base isn't 100 percent new, but a ton of work has gone into it by [developer] 343."
Spencer also told the site that Microsoft's talked about making a Halo 2 HD remake, and that it's not the company's intention to annualise the franchise.
"Obviously Halo 2 is one that we've talked about," he said. "I wouldn't say this is a strategy for us to go back and remake Xbox 1 games. This was the 10th Anniversary of Halo so it made sense.
"People shouldn't look at Anniversary as part of an annualised franchise. I love the fact we're doing the Anniversary edition because I loved Halo 1. We just looked at it and thought it needed to be refreshed. It wasn't part of us trying to get into an annualised rhythm with the franchise. It will be done in time for this holiday that is the 10th Anniversary for Halo. It felt like a good time to celebrate it."