The latest Halo 2 autoupdate is coming online now. This is a free autoupdate for Xbox Live members. You can read details about what the autoupdate contains in this article on Bungie .net
Not everyone will receive the autoupdate at the same time.
Everyone will receive the autoupdate by 2:00p PT/5:00p ET.
There is nothing you can do to force getting this AU early…so sit tight and you will get it.