It is not mandatory and I'm quite sure there are still many players with big bets that have not completed any KYC but Stake tries to make players do KYC by offering some bonuses to those who want to complete KYC.
Example from the VIP forum challenge, anyone who have completed verification level 1 will get 10% extra reward, level 2 100% extra reward and level 3 150% extra reward.
The bonuses applies almost in all available promotions so basically it is a very good offer to anyone who are OK with KYC.
It is not mandatory in certain situations and I agree with that logic, it should not be forced to people and unfortunately we are seeing more and more places start forcing KYC to people which is a damn shame, I rather not give my information to any place as long as I can avoid it, why would I basically declare to the whole world about where I gamble and how much I gamble and what I gamble basically everything about me, even on exchanges it was a hard move towards KYC but now we are basically forced everywhere so I can't do much.
In other news we are talking about still not being able to participate in many things unless we give our KYC which is still not a good deal, I rather have some of my privacy kept while still enjoying gambling but it is getting harder and harder, I can probably just gamble regular games without anything else, but then I am missing out on so many promotions here as well.