The Preview for Windows 8.1 is available to those that want it.
A caveat, though:
Yes. Windows 8.1 Preview and Windows RT 8.1 Preview are stable and have been thoroughly tested, but aren’t the finished product. Your PC could crash and you could lose important files. You should back up your data and you shouldn’t test the preview on your primary home or business PC. You might also encounter problems like:
Software that doesn’t install or work correctly, including antivirus or security programs.
Printers, video cards, or other hardware that doesn’t work.
Difficulty accessing corporate or home networks.
Damage to some of your files.
You should carefully balance the risks and rewards of trying out the preview before you install it.