Or is there some sort of cut off date when people who buy 8.1 after it don't get 10 for free?
I heard MSFT is debating it due to pirate. So, I think it's a no for right now.
"cut off date"
There wouldn't be a cut-off date. The last I have heard was that you have to upgrade within a year of Windows 10 release.
Agree with Nerdman88 here. There was an announcement that there will be a 'grace period' for a free upgrade, something in the range of the first year after release. Once that 'grace period' has expired, you would have to purchase it. The free upgrade is being offered for both Win 7 & Win 8.
This says it best.
yes but only for 1 year you can enjoy windows 10 .
Nope you get it fully licensed free. As long as your copy is legitimate