This means there’s a 13GB difference, but thanks to 343 Industries Studio Head, Josh Holmes we now have some clarification. According to Holmes, there will a day one multiplayer patch that is 9GB. It is safe to say to have at least 60GB of free space before installing the game.
Interesting fact, the reason why we receive so many day one patches is because Blu-ray discs can only store up to 50GB of storage. Everything beyond 50GB needs to be downloaded, unless you want an unfinished game.
Halo 5: Guardians is rapidly approaching, if you decided to digitally download the game, you can start pre-loading it now. If you rather a physical version, you will be able to pick it up October 26th.