From Breitbart.com:

President Bashar al-Assad’s state-run Syrian news agency admitted Sunday that the Tabqa air base had indeed been lost and that Syrian forces had successfully regrouped “after evacuating the airport.”

Tabqa is home to an array of fighter jets, helicopters, tanks, artillery, and large caches of ammunition. It is unknown if Syrian forces were able to secure their armaments before conceding defeat and evacuating the base.