Windows 8 RTM is available for developers

If you have an MSDN Subscription or a TechNet Professional Subscription, the Windows 8 RTM is available. For info on other programs see the Windows 8 has reached the RTM milestone post on Windows Team blog.

If you are not part of one of these programs, you can download the 90-day evaluation of the Windows 8 Enterprise edition for developers. This is available now from the Windows Dev Center download page along with Visual Studio Express 2012, Windows 8 design assets, code samples, and all the related tools and SDK’s needed to build apps.

If you use the evaluation version, you are recommended installing it on separate drive or partition or in a VM. This way you’ll be able to upgrade from your original OS to the Windows 8 RTM when it becomes available in October. If you don’t, then you’ll need to reinstall from scratch when you decide to move to the full version. Make sure you read all the details on thedownload page.

Source: Windows 8 app developer blog - Windows 8 RTM is available for developers.