Teams Support of Internal Guest User (formerly known as State 3 and State 4 accounts)
Teams is adding support for Azure AD’s internal guest users (users whose UserType value is “guest” with credentials managed by the host organization either on-prem or in the cloud). These internal user would sign-into Teams like any other users and would be able to collaborate with other users in the host organization.
Note: This change is to support legacy scenarios (formerly known as guest user state 3 and 4), that may have blocked organizations from utilizing internal guest access previously. This change does not impact existing guest access settings.