https://blogs.office.com/2017/04/06/whats-new-in-office-365-groups-for-april-2017/
Hidden membership—If you want group membership to be confidential (for example, if the members are students), you can hide the Office 365 group members from users who aren’t members of the group.
https://technet.microsoft.com/en-us/library/mt219359(v=exchg.160).aspx New-UnifiedGroup -HiddenGroupMembershipEnabled
Using this exchange online powershell to create O365 group with hidden membership?
Will graph API support it?
Thanks!