We currently have a 2012 R2 KMS server, which (using the 2012 R2 kms host key) activates all of our 2012/2012r2 servers and all of our win8/win8.1 enterprise workstations.

We are preparing to roll out a pilot of Win10 enterprise, but because Win10 Server is delayed until later, we won't be able to get server keys and use those to downlevel activate clients and servers together.

How will we do this?  I know we'll be able to patch our 2012r2 KMS server and install the win10 KMS key on it, but that will only activate client OSes and our servers will fall out of activation...

I know we'll be able to patch our 2012r2 KMS server and install the win10 KMS key on it, but that will only activate client OSes and our servers will fall out of activation...

Never in the past, has it been possible to insert/install a "client" OS KMSHost pkey upon a Server OS.
Unless MSFT have changed things, you can't do that.

So we'll all need to setup a Win10 Enterprise box as a Win10 KMShost, and have everything discover/point to that, as well as our existing KMShost(s).

[which we did something similar, when Vista was released but WS2008 was slow to come along]

Until WS2016 is released, or, if MSFT do something different for us..

https://social.technet.microsoft.com/Forums/en-US/e2510de8-858a-4a46-88f4-b6a67ba90797/kms-and-windows-10-keys?forum=winserver8g

Microsoft did release this update in July for Windows Server 2012 R2 :

https://support.microsoft.com/en-us/kb/3058168/en-us "Update that enables Windows 8.1 and Windows 8 KMS hosts to activate a later version of Windows"

This update leads me to believe that once this patch is installed that existing KMS hosts will be able to activate later versions of Windows.  And in fact I find this today on my KMS server:

Name: Windows(R), ServerDatacenter edition
Description: Windows(R) Operating System, VOLUME_KMS_2012-R2_WIN10 channel

This license is not in use.
License Status: Unlicensed

I suspect all that I need is the right 2012 R2 key that has support for Windows 10 and there is some indications that it exists, however I cannot find it in VLCS today.  The name reportedly is "Windows Srv 2012R2 DataCtr/Std KMS for Windows 10".

Interesting.  We've requested our kms keys from the volume licensing center (they don't provide them automatically anymore, only mak for some strange reason) but they haven't shown up yet.  Would we be able to use our Win10 client key for Active Directory Based Activation and continue using our 2012r2 key on our kms server?  that would avoid having two kms servers right?

Interesting.  We've requested our kms keys from the volume licensing center (they don't provide them automatically anymore, only mak for some strange reason) but they haven't shown up yet.  Would we be able to use our Win10 client key for Active Directory Based Activation and continue using our 2012r2 key on our kms server?  that would avoid having two kms servers right?

ADBA should work ok, but that still may require a Win10 Enterprise machine to create and populate the AD object.
MSFT documentation, blogs, and guides, only ever seem to show ADBA examples using a server OS.

Interesting to see if VLSC issue you a key which will work on WS2012R2 for Win10. Let us know?

I'll be requesting the same on Monday. (It's been some time since I needed to get a new KMShost pkey, I forgot that MSFT said they wouldn't add them into VLSC by default any more)

(But, they added in the Win10 and VDA10 KMShost pkeys to my VLSC without me asking...)

Will let you know... Wonder why we didn't get our keys hmm...

Wonder why we didn't get our keys hmm...

Is your Software Assurance still current?

Ya our win10 mak keys and downloads are there

Thanks to a list I'm on someone described where to find the right key in VLSC.   It's not in the CSV and it's not in the "Downloads and Keys" section.  It's under Licenses -> Relationship Summary -> [Your Licensing Enrolment] -> Product Keys.

No different - only mak keys in that location as well for win10.  You have to request kms keys these days afaik.

Thanks to a list I'm on someone described where to find the right key in VLSC.   It's not in the CSV and it's not in the "Downloads and Keys" section.  It's under Licenses -> Relationship Summary -> [Your Licensing Enrolment] -> Product Keys.

Excellent find, and thanks for sharing, mine is there too, named "Windows Srv 2012R2 DataCtr/Std KMS for Windows 10", and it's a different key compared to all the other Win10/VDA10 KMS host keys listed in my VLSC.

wonder why I only have mak =(

wonder why I only have mak =(

Do you have Open, Select or Enterprise Agreement?
I have EA and Select.
I think Open, has to request the KMS Host keys (that's what a popup in VLSC told me).

ok yeah, we are all open...  hopefully they'll get to my request soon - thanks!