It seems that the Russian Aerospace Force (VKS) has deployed it's latest fighter in Syria. A couple of the prototypes were seen arriving at Hmeymin escorted by a Su-35. The Sukhoi Su-57, fifth generation fighter, has not even entered service. It has not been officialy confirmed, and in the past there were fake news on similar stores (MiG-31s in Syria). Perhaps it is better to take the information with a pinch of salt.
It does not make much sense to deploy the type in Syria. Perhaps the company wants to get the label "deployed in combat conditions". Some of the prototypes should be able to carry out combat missionss as they already have the combat equipment.
It would not be the first time that a combat aircraft enters combat before officialy entering into service. The Su-25 was deployed in Afghanistan before completing the testing.