How do I access UnityEngine.Networking?

I’m trying to access the NetworkIdentity class, but I’m having trouble getting to it. I can’t assign it in the editor because it doesn’t come up when I search it. I can’t assign it in code, since intellisense doesn’t auto-complete it when I try to use UnityEngine.Networking (manually typing it in also results in a “namespace not found” error).

I’m currently using Unity 5.0.1f. I was under the impression that this system was actually implemented specifically for Unity 5, but has it already been filtered out?

It was introduced in Unity 5.1, as confirmed via a trivial web search: https://unity3d.com/unity/whats-new/unity-5.1