If you are using KMS server or stuff like creating templates without using you licens key you can use KMS setup keys. This keys cannot be activated but works for deployment scenarios where you have to type in a key under installation. For instance Windows Server 2012 and 2012 R2 ask for a key if deploy With MDT, then you can use the keys.
Windows Clients
Windows 10 Professional | W269N-WFGWX-YVC9B-4J6C9-T83GX |
Windows 10 Enterprise | NPPR9-FWDCX-D2C8J-H872K-2YT43 |
Windows 10 Education | NW6C2-QMPVW-D7KKK-3GKT6-VCFB2 |
Windows 10 Enterprise 2015 LTSB | WNMTR-4C88C-JK8YV-HQ7T2-76DF9 |
Windows 8.1 Professional | GCRJD-8NW9H-F2CDX-CCM8D-9D6T9 |
Windows 8.1 Enterprise | MHF9N-XY6XB-WVXMC-BTDCT-MKKG7 |
Windows 8 Professional | NG4HW-VH26C-733KW-K6F98-J8CK4 |
Windows 8 Enterprise | 32JNW-9KQ84-P47T8-D8GGY-CWCK7 |
Windows 7 Professional | FJ82H-XT6CR-J8D7P-XQJJ2-GPDD4 |
Windows 7 Enterprise | 33PXH-7Y6KF-2VJC9-XBBR8-HVTHH |
Windows Server
Windows Server 2012 R2 Server Standard | D2N9P-3P6X9-2R39C-7RTCD-MDVJX |
Windows Server 2012 R2 Datacenter | W3GGN-FT8W3-Y4M27-J84CP-Q3VJ9 |
Windows Server 2012 Server Standard | XC9B7-NBPP2-83J2H-RHMBY-92BT4 |
Windows Server 2012 Datacenter | 48HP8-DN98B-MYWDG-T2DCC-8W83P |
Windows Server 2008 R2 Standard | YC6KT-GKW9T-YTKYR-T4X34-R7VHC |
Windows Server 2008 R2 Enterprise | 489J6-VHDMP-X63PK-3K798-CPX3Y |
Windows Server 2008 R2 Datacenter | 74YFP-3QFB3-KQT8W-PMXWJ-7M648 |
Full list and info can be found here:
http://technet.microsoft.com/en-us/library/jj612867.aspx
And to add it to the unattend.xml?