The RTM version of Windows 8.1 will be available in the mid of October while Microsoft hasn't commented on the release date of first major update of Windows 8.
As per schedule, the RTM version of Windows 8.1 will be delivered to OEM partners later this month while the general public will have to wait for at least another 45 days.
According to sources communicated by ZDNet’s Mary Jo Foley, Microsoft has now completed the development of the operating system and will release the RTM (Release to Manufacturing) of Windows 8.1 to OEMs at the end of August. So the partners will be able to start their testing to ensure the perfect compatibility of drivers and software with the Windows 8.1 upgrade. The new products (PCs, notebooks and tablets) will come onto the market in mid-October with the final release of Windows 8.1, and at the same time users will able to download and install the update from the Windows Store on their computers running Windows 8.
Surprisingly Microsoft has no plans to distribute the OS via MSDN and TechNet (soon to be closed on August 31) channels, and it is not clear why the subscribers will not get the preferential treatment this time. Perhaps it should reduce the chances of finding pirated copies on file sharing sites, but does it really matter? Since, the Windows 8.1 will be available at absolutely no cost.
According to rumors, there would also be a big post-RTM update between late August and early September, and the same conceivable roadmap for Windows Server 2012 R2.
Recently leaked builds of Windows 8.1 have revealed a number of changes, including new communication app, slightly restyled Modern apps and some bug fixes. Therefore, it seems the final version should not include substantial differences.