Not sure when but obviously they're trying to get you hooked so you'll bump up your membership to a higher level. There are a certain number of free videos on site that anyone can watch but full video access is still limited to diamond or at least that's what the membership page says.
Chess Mentor on Gold Membership
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I'm on gold subscription for like 3 months already and I know that I shouldn't have access to chess mentor nor videos.
But to my surprise, I was able to view a complete video and 3 mentor courses via Study Plans. When did chess.com give this niceties for goldies?