Microsoft Retired MS-900 and Replaced It with AB-900 — Here's What Actually Changed
On March 31, 2026, Microsoft quietly retired the MS-900 exam, the Microsoft 365 Fundamentals certification that had been the standard entry point into the Microsoft ecosystem for years. In its place came something new: the AB-900 , officially titled Microsoft 365 Copilot and Agent Administration Fundamentals . Most people assumed it was a light rebrand. It is not. These two certifications share roughly 20 to 25% of their content . The rest is completely new territory — AI governance, agent lifecycle management, Microsoft Purview at depth, and Copilot administration tools that did not even exist when MS-900 was relevant. If you are planning your certification path and have been treating AB-900 like a refreshed MS-900 with a new number, you need to course-correct now. This article breaks down exactly what changed, what stayed, where the difficulty gap sits, and what it means for your career in 2026. Why Microsoft Killed the MS-900 Before getting into the differences, it helps to underst...