System.Threading.Tasks

 namespace System.Threading.Tasks {
     public static class TaskExtensions {
-        public static ConfiguredAsyncEnumerable<T> ConfigureAwait<T>(this IAsyncEnumerable<T> source, bool continueOnCapturedContext);

+        public static ConfiguredCancelableAsyncEnumerable<T> ConfigureAwait<T>(this IAsyncEnumerable<T> source, bool continueOnCapturedContext);
+        public static ConfiguredCancelableAsyncEnumerable<T> WithCancellation<T>(this IAsyncEnumerable<T> source, CancellationToken cancellationToken);
     }
 }