diff --git a/src/ReC.Client/TaskSyncExtensions.cs b/src/ReC.Client/TaskSyncExtensions.cs
index 2effd36..e9edcad 100644
--- a/src/ReC.Client/TaskSyncExtensions.cs
+++ b/src/ReC.Client/TaskSyncExtensions.cs
@@ -7,12 +7,14 @@ namespace ReC.Client
     /// <summary>
     /// Provides synchronous wrappers for Task-based operations.
     /// </summary>
+    [System.Obsolete("Synchronous blocking helpers (Task.Sync) are no longer recommended. These methods can cause deadlocks or unexpected behavior. Rewrite calling code to use async/await (e.g. async Task tests). This helper class will be removed in a future release.", false)]
     public static class TaskSyncExtensions
     {
         /// <summary>
         /// Blocks until the task completes and propagates any exception.
         /// </summary>
         /// <param name="task">The task to wait for.</param>
+        [System.Obsolete("Use async/await instead of synchronous blocking. This method can cause deadlocks.", false)]
         public static void Sync(this Task task) => task.ConfigureAwait(false).GetAwaiter().GetResult();
 
         /// <summary>
@@ -21,6 +23,7 @@ namespace ReC.Client
         /// <typeparam name="TResult">The type of the task result.</typeparam>
         /// <param name="task">The task to wait for.</param>
         /// <returns>The result of the completed task.</returns>
+        [System.Obsolete("Use async/await instead of synchronous blocking. This method can cause deadlocks.", false)]
         public static TResult Sync<TResult>(this Task<TResult> task) => task.ConfigureAwait(false).GetAwaiter().GetResult();
     }
 }
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