ITaskObservable<T> public interface ITaskObservable<T> : IObservable<T> Extension of the IObservable<T> interface compatible with async method return types. Documentation Code using System.Runtime.CompilerServices; namespace System.Reactive { [System.Runtime.CompilerServices.NullableContext(1)] [AsyncMethodBuilder(typeof(TaskObservableMethodBuilder<>))] public interface ITaskObservable<[System.Runtime.CompilerServices.Nullable(2)] out T> : IObservable<T> { ITaskObservableAwaiter<T> GetAwaiter(); } }