If you have a Technet or a MSDN account you can download Windows 8.1 & Server 2012 R2 Preview
Windows 8.1 Preview
Server 2012 R2 Preview
Day: June 27, 2013
System Center 2012 R2 Preview Availably
If you have a Technet or MSDN account you can download System Center 2012 R2 Preview 
ou
ADK for Windows 8.1 Preview Available
Here is a quick summary of the changes in ADK for Windows 8.1. MDT 2013 and ConfigMgr 2012 R2 requires ADK for Windows 8.1.
Windows 8.1 Image Size (Preview)
- Windows 8.1 Preview Code Image (x86), 2.13 GB (WIM), 7.65 GB expanded on disk.
WinPE 5.0
- Profiling in WinPE 5.0 is removed
- WinPE 5.0 x64 supports 4 TB of RAM (still 64 GB for x86)
- Scratchspace set automatically to 512 MB when having more than 1 GB of RAM, otherwise 32 MB
USMT 6.3
- Support for Windows 8.1
- You cannot use USMT 6.3 to migrate settings from Windows XP to Windows 8.1
- Supports Office 2013 (hotfix available for USMT 5.0).
Windows 8.1 Upgrade / Update
- You are likely to have more free space available on the disk after upgrading Windows 8 to Windows 8.1
- Windows 8.1 upgrade time, less than 20 minutes
Misc. Updates
- Export compressed recovery image (/Export-Image)
- Cleanup base components when superseded. (/StartComponentCleanup /ResetBase)