As far as I can make out if you have the latest build 10240 and all the updates you have the final version. If you open a command prompt and type in
slmgr /xpr ( there is a space between the r and / ) it will open a script box telling you how long the activation is. On my sons computer which he did not update from a registered copy but just used the earlier insider build which updated to the latest 10240 it says that it is permanently activated.
on my machine I updated from windows 8.1 Pro and it says the same thing. Hope this is of help.