Entra Connect Sync: Upgrade by 30 September 2026

Starting September 30, 2026, Microsoft Entra Connect Sync will stop synchronizing if your sync server is running a version below 2.5.79.0. Microsoft outlines this in its documentation under the heading 'Mandatory Upgrade Required': All synchronization services will fail and remain non-operational until you upgrade.

This is not a soft support boundary, but a hard stop. Between the cutoff date and the actual upgrade, your tenant will not synchronize: new accounts, password hash changes, attribute changes, and group memberships will no longer sync to Entra ID during this gap.

The background is backend hardening. Version 2.5.79.0 was released as early as May 2025 and is the first version to work with the modified service. Those who have the auto-upgrade function enabled have been receiving updates in waves since September 2023 and are mostly on the safe side. The situation becomes critical for servers where auto-upgrade was disabled or failed, for example, after manual adjustments to the sync rules.

You can check your status in just a few minutes. Open the Synchronization Service Manager or look up the installed version number in Programs and Features and compare it with 2.5.79.0.

An important point for planning: 2.5.79.0 is just the baseline, not the target. Even this version will reach its end of support on October 23, 2026. Anyone rushing to upgrade to exactly 2.5.79.0 today is only buying themselves about three weeks. A more sensible approach is to jump directly to a current build from the Microsoft Entra Admin Center, as the MSI installation file is available exclusively there. Prerequisites are .NET Framework 4.7.2 and TLS 1.2.

The next mandatory deadline is also set. By April 7, 2027, you must upgrade to version 2.6.84.0 or higher and configure app-based authentication, otherwise synchronization will stop again. If you’re already scheduling a maintenance window, you can take care of both tasks in one go.

The in-place upgrade runs without critical issues, but it does have side effects. The regular delta sync pauses during installation, while password synchronization continues. If you had modified the default sync rules, the upgrade resets them to their original state and forces a full synchronization. That’s why a weekend maintenance window is the safer choice.

For tenants with auto-upgrade enabled, today is probably not a holiday. Everyone else should immediately check their version, upgrade to a current build instead of just the minimum version, and mark April 7, 2027, for version 2.6.84.0 plus app-based authentication in their calendar. Those already planning a pure cloud synchronization should now evaluate switching to Entra Cloud Sync.