Today, a blog reader notified me that Microsoft released an update that extends KMS for Windows 7 Service Pack 1 (SP1) and Windows Server 2008 R2 SP1 to enable the activation of Windows 10-based clients. Find it here.
I blogged about the update for Windows Server 2012 (R2) and Windows 8/8.1 before but now these older operating systems can also serve as KMS servers for Windows 10. All you need is the update that enables Windows 7 and Windows Server 2008 R2 KMS hosts to activate Windows 10 as discussed in KB3079821
Until now the workaround was to leverage Active Directory based activation for Windows 10 whilst you left your KMS server in place for the older clients. That works well and I have used it before. But with this update you can use your older KMS servers for all activations of windows clients.