Microsoft will be ready with Windows 8.1 RTM (release to market) version in August, according to the recent company blog post. According to the report, OEMs will be getting it in August while retail and products from OEMs with Windows 8.1 could get it in October, when Windows 8.1 is scheduled to officially launch.
OEMs usually get a disc image of the software in order to make certificates of authenticity for each product and modify it to include product specific drivers. An early ship to OEMs is not strange but the good part of the story is that we should see products with Windows 8.1 from day one.

Microsoft still refers to the Windows 8.1 as an update that "refines the vision of Windows 8". In case you missed it earlier, Microsoft has released Windows 8.1 Release Preview two weeks ago, in case you want to check it out.



Source: Windows Blog.