Microsoft is giving away Halo 3 for free to any Xbox Live Gold subscriber until October 31, as part of its ongoing Games with Gold promotion.
The usual price for the game is $14.99, but Microsoft is looking to add to the rank and file of its Xbox Live Gold subscriptions.
The "Alien" director will serve as executive producer on the project, which is due to be released later this year.
The minds behind Halo, one of the most successful game franchises ever made, hope to strike it again with a massive new game being bankrolled in part by Activision Blizzard.
Halo was first released in 2001 for the Xbox, and has racked up some impressive numbers over the succeeding 11 years.
Microsoft and Activision are teaming up to give 'Guitar Hero III' players a free download of the 'Halo' theme song.
Sony might be leading the console market, but Microsoft's free game offer with the purchase of a new Xbox One could make a difference.
The console will bring with it more than 70 games, including exclusive content, free-to-play games, and "blockbuster" titles, says Microsoft.
Program that gives Xbox Live subscribers free games twice a month is being extended by Microsoft indefinitely.
Believe it or not, Halo 4 might be the start of an even better trilogy than before.