hyper-v compatibility between windows 8.1 and windows 10

I reserved free upgrade copy for windows 10 on windows 8.1, but will my virtual machines on windows 8.1 be compatible to windows 10? how about if I decide to downgrade windows 10 to windows 8.1, will virtual machines running on windows 8.1 and 10 compatible back and forth?

Same question, but different versions, how about VMs on Windows 2012, 2012 R2, and 2016? VMs can be moved  back and forth?
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JohnBusiness Consultant (Owner)Commented:
Windows 10 is still beta and I am not sure what the hyper-v version will be. But you cannot go back to V5 from V6 according to the Microsoft Article below.


Windows 10 works very well - I have it running. So once you get started there should be no reason to move back to Windows 8.1 (which I have running just fine right now).

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crcsupportAuthor Commented:
"You can no longer add a node to the Hyper-V Cluster that is running Windows Server 2012 R2. "
Wow, so it means,  Just like AD, one server holds the entire AD functional level upgrade.
crcsupportAuthor Commented:
Does it mean that I can create and add a VM on V5 on Windows 10? The reason why I'm concerned is because,
I like to be flexible moving VMs between Windows 8.1 and Windows 10. The link assumes it's a cluster environment.
Let's say I have 2 Windows 8.1 computers now. I have VMs running on both. I upgraded one host to Windows 10. Then, I should end up forced to upgrade the 2nd host as well.
I think I have to test the cmdlets once I get windows 10.

get-vm | select name, version
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JohnBusiness Consultant (Owner)Commented:
I think I would much more inclined to test Windows 10 on a separate machine.  I am going by the article, and I use VMware Workstation. Machines in VMware CAN move along with Workstation from one operating system / machine to another.
Philip ElderTechnical Architect - HA/Compute/StorageCommented:
As a suggestion have your OS on one partition and your VMs on another.

When it comes time to upgrade the host OS do so on the first partition. If things blow up and a fresh install is needed no loss.

The import process in Hyper-V is vastly improved with 2012 RTM/R2 and Win 8.1 onwards.

Once the fresh OS or upgraded OS is configured you can import the VMs on the other partition if they don't show up post change.
John's link answers it in clear words. You can use 2012R2 machines (V5) on the new server without upgrading the version. You can also re-use them on 2012R2 afterwards. Only if you want to use new features, you will have to upgrade the machines to V6 and then, there's no going back.
David Johnson, CD, MVPOwnerCommented:
don't upgrade the integration tools until you are ready to ditch Windows 8.1
JohnBusiness Consultant (Owner)Commented:
@crcsupport  - Thanks and I was happy to assist you. Good luck with Windows 10. It is a good operating system (so also were Windows 7 and 8.1)
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