[Update] Microsoft has released an official statement to OXM regarding the alleged Halo 2 Anniversary leak. The statement reads:
Other than confirming that your Halo journey on Xbox One begins in 2014, we have made no announcements related to specific titles. Any report or listing to the contrary is based solely on speculation and rumour.
[Original] Despite the fact that Microsoft has not yet announced the rumored Halo 2 Anniversary for Xbox One, one online store is ready to take your money if you're interested in reserving a copy.
Microsoft still has yet to announce the existence of an HD remake of Halo 2, but by all accounts it looks like we may very well get it by year's end.