What do you mean by ring 4.
If your question is on how many users can be created in Azure AD, then you can refer as below,
By default, a maximum of 50,000 Azure AD resources can be created in a single tenant by users of the Azure Active Directory Free edition. If you have at least one verified domain, the default Azure AD service quota for your organization is extended to 300,000 Azure AD resources.
There are other restrictions as well in terms of Azure AD tenant. You can refer below article for the same,
Let me know if you have any further questions on this.
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