We were just talking about this earlier today. Windows 8.1 is set to roll out to current Windows 8 users on October 17th, with general availability on October 18th, however, Microsoft will also be rolling out a GA Rollup A update for the operating system.
Even though Windows 8.1 has reached RTM and is nearing its general availability, Microsoft will also be releasing a "GA Rollup A" update upon the release of the operating system. Call it an update for the update, if you will. This update will finalize the Windows 8.1 code, since technically Windows 8.1 isn't finished yet even though it hit RTM. You can read more about this update here.
Now, it appears that this update has leaked onto the internet. The x64 variant of this update has leaked and weighs in at about 232MB. An x86 and ARM version of the update has also leaked, for Windows 8.1 32bit and Windows RT 8.1. The package contains three patches, labeled KB2894179, KB2883200, and KB2894029.
We wont post download links, however, you can head over to the VIA link below to do a little 'investigation' of your own to find the download. Microsoft is set to roll out this update via Windows Update soon.