<PackageReference Include="System.Reactive" Version="7.0.0-preview.1" />

System.Reactive.Subjects.BehaviorSubject<T>

public sealed class BehaviorSubject<T> : SubjectBase<T>
namespace System.Reactive.Subjects { public sealed class BehaviorSubject<[Nullable(2)] T> : SubjectBase<T> { public T Value { get; } public BehaviorSubject(T value); public bool TryGetValue(out T value); } }