This is taken from Windows 8 blog:
So when will folks be able to get their hands on the new Windows 8 RTM code?
People will be able get Windows 8 starting on October 26th either by upgrading for $39.99 or on a new PC or device. And if you buy an eligible Windows 7 PC today, you will be able to purchase an upgrade to Windows 8 Pro for $14.99 (U.S.) through the Windows Upgrade Offer.
However, we have a number of programs that provides various audiences early access to the Windows 8 RTM code to help prepare for Windows 8 as it enters the marketplace this fall:
◦August 15th: Developers will be able to download the final version of Windows 8 via your MSDN subscriptions.
◦August 15th: IT professionals testing Windows 8 in organizations will be able to access the final version of Windows 8 through your TechNet subscriptions.
◦August 16th: Customers with existing Microsoft Software Assurance for Windows will be able to download Windows 8 Enterprise edition through the Volume License Service Center (VLSC), allowing you to test, pilot and begin adopting Windows 8 Enterprise within your organization.
◦August 16th: Microsoft Partner Network members will have access to Windows 8.
◦August 20th: Microsoft Action Pack Providers (MAPS) receive access to Windows 8.
◦September 1st: Volume License customers without Software Assurance will be able to purchase Windows 8 through Microsoft Volume License Resellers.
Please note: if a program you are in is not mentioned, please be patient as dates for Windows 8 RTM code availability for other programs will be communicated when the information becomes available.
For more information on what the RTM of Windows 8 means for businesses including Volume License customers, see this blog post from Erwin Visser on the Windows for your Business Blog. This post, also from Erwin, on how Windows 8 will work in your business is also a good post to read.
On August 15th, developers will be able to visit the Windows Dev Center to get access to all the tools and resources they need including the final build of Visual Studio 2012 to design, build, and sell apps in the Windows Store. Keep your eyes on the Windows Store for developers blog and Windows 8 app developer blog for more information. I am super excited to see the kinds of apps developers build for Windows 8! If you have the Windows 8 Release Preview installed, you can already check out some apps developers have created for Windows 8 today.
In the meantime, if you’d like to give a pre-release version of Windows 8 a test-run, feel free to download the Windows 8 Release Preview! You can also read about my personal experience with the Windows 8 Release Preview here (hint: I put it on all my PCs!).