Windows 8.1 Preview

Does defraggler support Windows 8.1 Preview? I don't want to screw up my PC with something that is meant for earlier versions of Windows.

Yep, it does.

But whenever running a program that effects the PC at the system level (and something you should be doing anyway) make sure you have a backup.

Also, it's not "fully compatible" until 8.1 is actual released (or RTM if there will be one, though that's not likely). So officially no it is not supported, but there really won't be any difference as (to the best of my knowledge) 8.1 is the same as 8 when it comes to fragmentation/defragmentation