Checking the game library there is a 4.9 GB download for Halo: MCC which suggests that Halo 4 is available now. Halo also tweeted #Halo4 to herald the game is available at last.
After the 4.9GB update is installed. Click on Halo 4 and try to launch the campaign. This will bring up a menu to install the campaign and multiplayer maps. Installing everything will then trigger a 15GB download to complete the installation.
Halo: MCC is now 118855 MB making it the second largest game in the studio collection so far. Even the popular Elder Scrolls: Online is not as large.
Halo 4 completes the Master Chief Collection which has been well received by the Steam community. The affordable price was a godsend for those who have a limited budget, the Master Chief Collection represents excellent value. 6 great games in one package is excellent bang for the buck. Small wonder that millions of copies have been sold.