Hi @Kamen ,
Azure AD is licensed per-user. This means that a proper license is required if a user benefits directly or indirectly from any feature covered by that license.
So if you are assigning roles to the groups with those users in it, or using other premium features such as Conditional Access that applies to those users, a Premium license is required. But if those features only apply to 50 of the users, you only need the licenses for those 50.
Feel free to speak with a licensing representative for pricing questions, though. It's free to speak with the billing team.
Let me know if this helps answer your question.
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