If your organization still relies on legacy Office add-ins built using the VSTO framework, it is time to pay attention. The "End of Life" (EOL) designation means the runtime will no longer receive updates, security fixes, or technical support.
For long-term stability, migrate away from VSTO entirely to the modern Office Add-ins platform (using HTML/JavaScript or Blazor). These run inside a sandboxed web view, are cross-platform (Windows, Mac, Web), and are actively maintained by Microsoft. visual studio 2010 tools for office runtime end of life
We are seeing a specific problem emerge in 2026: Orphaned VSTO solutions . A developer built an Excel add-in for a trading desk in 2012 using VSTO 2010. That developer left the company. The add-in still works—barely. When IT upgrades the company to Windows 11 24H2, the add-in fails silently because the VSTO 2010 runtime triggers a Windows Defender Application Control (WDAC) flag. If your organization still relies on legacy Office