diff --git a/src/contrib/cluster/Akka.Cluster.Tools/PublishSubscribe/Internal/TopicMessages.cs b/src/contrib/cluster/Akka.Cluster.Tools/PublishSubscribe/Internal/TopicMessages.cs
index a2a80319f0b..33f40e1fe19 100644
--- a/src/contrib/cluster/Akka.Cluster.Tools/PublishSubscribe/Internal/TopicMessages.cs
+++ b/src/contrib/cluster/Akka.Cluster.Tools/PublishSubscribe/Internal/TopicMessages.cs
@@ -10,6 +10,7 @@
 using System.Collections.Immutable;
 using System.Linq;
 using Akka.Actor;
+using Akka.Annotations;
 using Akka.Event;
 using Akka.Routing;
 
@@ -42,9 +43,10 @@ private Count() { }
     }
 
     /// <summary>
-    /// TBD
+    /// Get all subscribers for a given topic.
     /// </summary>
-    internal sealed class CountSubscribers
+    [ApiMayChange]
+    public sealed class CountSubscribers
     {
         public string Topic { get; }
 
diff --git a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterTools.DotNet.verified.txt b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterTools.DotNet.verified.txt
index 9527f9cd6be..d91360aef5c 100644
--- a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterTools.DotNet.verified.txt
+++ b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterTools.DotNet.verified.txt
@@ -318,6 +318,15 @@ namespace Akka.Cluster.Tools.PublishSubscribe
         public override string ToString() { }
     }
 }
+namespace Akka.Cluster.Tools.PublishSubscribe.Internal
+{
+    [Akka.Annotations.ApiMayChangeAttribute()]
+    public sealed class CountSubscribers
+    {
+        public CountSubscribers(string topic) { }
+        public string Topic { get; }
+    }
+}
 namespace Akka.Cluster.Tools.PublishSubscribe.Serialization
 {
     public class DistributedPubSubMessageSerializer : Akka.Serialization.SerializerWithStringManifest
diff --git a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterTools.Net.verified.txt b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterTools.Net.verified.txt
index 246186de841..c891d1dc5da 100644
--- a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterTools.Net.verified.txt
+++ b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterTools.Net.verified.txt
@@ -318,6 +318,15 @@ namespace Akka.Cluster.Tools.PublishSubscribe
         public override string ToString() { }
     }
 }
+namespace Akka.Cluster.Tools.PublishSubscribe.Internal
+{
+    [Akka.Annotations.ApiMayChangeAttribute()]
+    public sealed class CountSubscribers
+    {
+        public CountSubscribers(string topic) { }
+        public string Topic { get; }
+    }
+}
 namespace Akka.Cluster.Tools.PublishSubscribe.Serialization
 {
     public class DistributedPubSubMessageSerializer : Akka.Serialization.SerializerWithStringManifest