Block sign-ups for Microsoft Stream
As an Office 365 Global Admin, you can prevent some or all users in your organization from being able to use Stream. This is typically done in cases where employees are already using Office 365 Video or if Stream has not been approved by all parts of your organization.
When a first user from any organization signs-up for Microsoft Stream using their corporate credentials, Microsoft Stream service is registered as an application in the organization's Office 365 tenant. The license is automatically assigned to the user who signed up. There are additional licenses available for the IT admin to assign to other users in the organization without them going through the sign up process.
Unlicense Microsoft Stream for specific users
For steps to unlicense users from the Office 365 admin center, see Remove licenses from users in Office 365 for business.
For steps to unlicense users by using PowerShell, see Managing Microsoft Stream licenses.
Even though as an admin you might have removed Microsoft Stream license from a user, they have the option to sign-up via a free trial and get access to your organization's Stream portal.
Turn off Microsoft Stream for everyone
As an Office 365 Global Admin, log in to the Azure portal with an administrator account.
In the Azure Active Directory (AAD) section, click Enterprise Application, and then in the Manage section, click All Applications.
Change the filters to Show All Applications with All Application Status, and then click Apply.
Search for the Microsoft Stream Service application from the list of applications, or search by the GUID 2634dd23-5e5a-431c-81ca-11710d9079f4 for Microsoft Stream Service.
Click the Microsoft Stream Service application, and then under Manage, click Properties.
Set Enabled for users to sign-in flag to No.
You have blocked access to all users for get access to the Microsoft Stream Service.
Experience when ad-hoc subscriptions are blocked
IT admins should be aware of the following scenario. If there are employees in your organization who have signed up for Microsoft Stream and then you block all ad-hoc subscriptions, new users who try to sign up for Microsoft Stream (and other viral services) will not be able to sign up and will see the following error:
However, users who had previously signed up will still be able to sign in and continue to use Microsoft Stream. To block sign in, you can either remove the licenses for each of these users or turn off the entire Microsoft Stream service.