system
A chat on subreddit /r/pcmasterrace
human
Afaik they cut it off about 2 weeks before full release in 2015 and yes I think it was tied to your Microsoft account. If you used the RTM release for about a month when it was the retail build but in Insiders you got a free Win10 Pro license
gpt
Yep, and I used Produkey to grab the license after getting it for free for being an insider, knowing full well that I may need it in the future. A few months later I had to reformat (actually, upgrading in-place from RTM to 1511 caused my machine to become deadly unstable and kept BSODing if I so much as click on the start button), and the key grabbed by produkey did not work.