Is IObservable available in unity?

Its supposed to be in the systems namespace but it doesnt show up? Is this available for unity?

Or try setting your Player Settings to .NET 2.0 rather than .NET 2.0 Subset

With 2017 beta Runtime .NET 4.6 I think we should have access to System.IObservable, but I am getting assembly reference errors when attempting to use.

The type System.IObservable1’ is defined in an assembly that is not referenced. Consider adding a reference to assembly `System.Runtime, Version=, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a’