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It is not required to purchase any Entra ID premium license for enforce MFA in your tenant.
Starting October 15th, 2024, enforcement for MFA at sign-in for the Azure portal , Entra portal and Intune portal will roll out gradually to all tenants.
There is no specific license required to receive this MFA requirement. However, there are some licensing requirements around what MFA methods are available to the users. For more information please see: Features and licenses for Microsoft Entra multifactor authentication .
Users in your tenant will still be able to use Authenticator app for MFA method without any licenses.
However, if you want users to use any additional methods for MFA in your tenant, then you will have to purchase Entra ID premium license.
Let us know if you have any further questions.
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