I don’t think so, Rama made a plugin that makes the selected meshes instanced.
Maybe there is a option/switch for actor meshes to be automatically instanced.
You can tell if you look at the number of draw calls.
-edit-
Perhaps there is a post from a dev somewhere that clarifies this?
Makes sense. I was previously under the impression that instanced meshes would only be one draw call. I have read that too many instances does impact performance though. Inside 3DS Max, you have to specify whether its an instance or a copy when you clone. I just always thought Unreal handled that automatically. I’ll have to look into it more when I next load up the editor. Would explain why my performance has never been as good as it could be 
I understand how instancing works but thanks for the links. I just always assumed it was automatic inside UE4.