Windows 8.1 will be coming as an update to all current Windows 8 users starting October 17th. It seems that the RTM version of Windows 8.1 as some have been testing will receive that final coating in the form of a big update that the final versions available to those who will upgrade to Windows 8.1 worldwide. The update has since leaked in internet forums and is said to be named ‘GA Rollup A’.
There is only the 64 bit variant out in the wild and it is just 232 MB and contains three patches: KB2894179, KB2883200, and KB2894029. the x86 and ARM versions are expected to weigh in at just 100 MB.
The update does not bring with major changes to the OS or anything widely noticeable but fixes some bugs and various OS components and is considered a QFE (Quick Fix Engineering) internally. It will be available via Windows Update on the day you receive your Windows 8.1 update (exactly a week from now).