diff --git a/src/contrib/cluster/Akka.Cluster.Sharding/Shard.cs b/src/contrib/cluster/Akka.Cluster.Sharding/Shard.cs
index 44611eb2a3a..352866a505d 100644
--- a/src/contrib/cluster/Akka.Cluster.Sharding/Shard.cs
+++ b/src/contrib/cluster/Akka.Cluster.Sharding/Shard.cs
@@ -10,6 +10,7 @@
 using System.Collections.Immutable;
 using System.Linq;
 using Akka.Actor;
+using Akka.Annotations;
 using Akka.Cluster.Sharding.Internal;
 using Akka.Coordination;
 using Akka.Event;
@@ -23,6 +24,13 @@ namespace Akka.Cluster.Sharding
     using EntityId = String;
     using ShardId = String;
 
+    /// <summary>
+    /// INTERNAL API
+    /// 
+    /// This actor creates children entity actors on demand that it is told to be
+    /// responsible for.
+    /// </summary>
+    [InternalStableApi]
     internal sealed class Shard : ActorBase, IWithTimers, IWithUnboundedStash
     {
         #region messages
diff --git a/src/contrib/cluster/Akka.Cluster.Sharding/ShardRegion.cs b/src/contrib/cluster/Akka.Cluster.Sharding/ShardRegion.cs
index 9540cf03e45..a0b3bc2f255 100644
--- a/src/contrib/cluster/Akka.Cluster.Sharding/ShardRegion.cs
+++ b/src/contrib/cluster/Akka.Cluster.Sharding/ShardRegion.cs
@@ -11,12 +11,12 @@
 using System.Linq;
 using System.Threading.Tasks;
 using Akka.Actor;
+using Akka.Annotations;
 using Akka.Cluster.Sharding.Internal;
 using Akka.Event;
 using Akka.Pattern;
 using Akka.Util;
 using Akka.Util.Internal;
-using Get = Akka.DistributedData.Get;
 
 namespace Akka.Cluster.Sharding
 {
@@ -25,11 +25,14 @@ namespace Akka.Cluster.Sharding
     using ShardId = String;
 
     /// <summary>
+    /// INTERNAL API
+    /// 
     /// This actor creates children shard actors on demand that it is told to be responsible for.
     /// The shard actors in turn create entity actors on demand.
     /// It delegates messages targeted to other shards to the responsible
     /// <see cref="ShardRegion"/> actor on other nodes.
     /// </summary>
+    [InternalStableApi]
     public sealed class ShardRegion : ActorBase, IWithTimers
     {
         #region messages
diff --git a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterSharding.DotNet.verified.txt b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterSharding.DotNet.verified.txt
index aedc47946f3..19325ac0b86 100644
--- a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterSharding.DotNet.verified.txt
+++ b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterSharding.DotNet.verified.txt
@@ -200,6 +200,7 @@ namespace Akka.Cluster.Sharding
     {
         public static Akka.Cluster.Sharding.IShardAllocationStrategy LeastShardAllocationStrategy(int absoluteLimit, double relativeLimit) { }
     }
+    [Akka.Annotations.InternalStableApiAttribute()]
     public sealed class ShardRegion : Akka.Actor.ActorBase, Akka.Actor.IWithTimers
     {
         public ShardRegion(string typeName, System.Func<string, Akka.Actor.Props> entityProps, Akka.Cluster.Sharding.ClusterShardingSettings settings, string coordinatorPath, Akka.Cluster.Sharding.ExtractEntityId extractEntityId, Akka.Cluster.Sharding.ExtractShardId extractShardId, object handOffStopMessage, Akka.Cluster.Sharding.Internal.IRememberEntitiesProvider rememberEntitiesProvider) { }
diff --git a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterSharding.Net.verified.txt b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterSharding.Net.verified.txt
index 8f4f60322f5..133e6d1a3aa 100644
--- a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterSharding.Net.verified.txt
+++ b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveClusterSharding.Net.verified.txt
@@ -200,6 +200,7 @@ namespace Akka.Cluster.Sharding
     {
         public static Akka.Cluster.Sharding.IShardAllocationStrategy LeastShardAllocationStrategy(int absoluteLimit, double relativeLimit) { }
     }
+    [Akka.Annotations.InternalStableApiAttribute()]
     public sealed class ShardRegion : Akka.Actor.ActorBase, Akka.Actor.IWithTimers
     {
         public ShardRegion(string typeName, System.Func<string, Akka.Actor.Props> entityProps, Akka.Cluster.Sharding.ClusterShardingSettings settings, string coordinatorPath, Akka.Cluster.Sharding.ExtractEntityId extractEntityId, Akka.Cluster.Sharding.ExtractShardId extractShardId, object handOffStopMessage, Akka.Cluster.Sharding.Internal.IRememberEntitiesProvider rememberEntitiesProvider) { }
diff --git a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.DotNet.verified.txt b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.DotNet.verified.txt
index cfc5130e2be..6f64e6b7071 100644
--- a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.DotNet.verified.txt
+++ b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.DotNet.verified.txt
@@ -2197,6 +2197,11 @@ namespace Akka.Annotations
     {
         public InternalApiAttribute() { }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Module | System.AttributeTargets.Class | System.AttributeTargets.Struct | System.AttributeTargets.Enum | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Property | System.AttributeTargets.Field | System.AttributeTargets.Interface | System.AttributeTargets.All, AllowMultiple=false, Inherited=true)]
+    public sealed class InternalStableApiAttribute : System.Attribute
+    {
+        public InternalStableApiAttribute() { }
+    }
 }
 namespace Akka.Configuration
 {
@@ -3204,7 +3209,7 @@ namespace Akka.Dispatch.SysMsg
         public Suspend() { }
         public override string ToString() { }
     }
-    [Akka.Annotations.InternalApiAttribute()]
+    [Akka.Annotations.InternalStableApiAttribute()]
     public abstract class SystemMessage : Akka.Actor.INoSerializationVerificationNeeded, Akka.Dispatch.SysMsg.ISystemMessage
     {
         protected SystemMessage() { }
@@ -5342,6 +5347,7 @@ namespace Akka.Util
         public static int StringHash(string s) { }
         public static int SymmetricHash<T>(System.Collections.Generic.IEnumerable<T> xs, uint seed) { }
     }
+    [Akka.Annotations.InternalStableApiAttribute()]
     [System.Runtime.CompilerServices.IsReadOnlyAttribute()]
     public struct Option<T>
     {
diff --git a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.Net.verified.txt b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.Net.verified.txt
index fb317ce392f..bddbd49935b 100644
--- a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.Net.verified.txt
+++ b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApproveCore.Net.verified.txt
@@ -2195,6 +2195,11 @@ namespace Akka.Annotations
     {
         public InternalApiAttribute() { }
     }
+    [System.AttributeUsageAttribute(System.AttributeTargets.Module | System.AttributeTargets.Class | System.AttributeTargets.Struct | System.AttributeTargets.Enum | System.AttributeTargets.Constructor | System.AttributeTargets.Method | System.AttributeTargets.Property | System.AttributeTargets.Field | System.AttributeTargets.Interface | System.AttributeTargets.All, AllowMultiple=false, Inherited=true)]
+    public sealed class InternalStableApiAttribute : System.Attribute
+    {
+        public InternalStableApiAttribute() { }
+    }
 }
 namespace Akka.Configuration
 {
@@ -3196,7 +3201,7 @@ namespace Akka.Dispatch.SysMsg
         public Suspend() { }
         public override string ToString() { }
     }
-    [Akka.Annotations.InternalApiAttribute()]
+    [Akka.Annotations.InternalStableApiAttribute()]
     public abstract class SystemMessage : Akka.Actor.INoSerializationVerificationNeeded, Akka.Dispatch.SysMsg.ISystemMessage
     {
         protected SystemMessage() { }
@@ -5332,6 +5337,7 @@ namespace Akka.Util
         public static int StringHash(string s) { }
         public static int SymmetricHash<T>(System.Collections.Generic.IEnumerable<T> xs, uint seed) { }
     }
+    [Akka.Annotations.InternalStableApiAttribute()]
     public struct Option<T>
     {
         public static readonly Akka.Util.Option<T> None;
diff --git a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApprovePersistence.DotNet.verified.txt b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApprovePersistence.DotNet.verified.txt
index 3b781e905ca..e231291dc65 100644
--- a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApprovePersistence.DotNet.verified.txt
+++ b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApprovePersistence.DotNet.verified.txt
@@ -377,8 +377,10 @@ namespace Akka.Persistence
         public Akka.Persistence.IStashOverflowStrategy DefaultInternalStashOverflowStrategy { get; }
         public Akka.Persistence.PersistenceSettings Settings { get; }
         public Akka.Persistence.Journal.EventAdapters AdaptersFor(string journalPluginId) { }
+        [Akka.Annotations.InternalStableApiAttribute()]
         public Akka.Actor.IActorRef JournalFor(string journalPluginId) { }
         public string PersistenceId(Akka.Actor.IActorRef actor) { }
+        [Akka.Annotations.InternalStableApiAttribute()]
         public Akka.Actor.IActorRef SnapshotStoreFor(string snapshotPluginId) { }
     }
     public sealed class PersistenceSettings : Akka.Actor.Settings
diff --git a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApprovePersistence.Net.verified.txt b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApprovePersistence.Net.verified.txt
index 6b52d35037c..4708abc85da 100644
--- a/src/core/Akka.API.Tests/verify/CoreAPISpec.ApprovePersistence.Net.verified.txt
+++ b/src/core/Akka.API.Tests/verify/CoreAPISpec.ApprovePersistence.Net.verified.txt
@@ -377,8 +377,10 @@ namespace Akka.Persistence
         public Akka.Persistence.IStashOverflowStrategy DefaultInternalStashOverflowStrategy { get; }
         public Akka.Persistence.PersistenceSettings Settings { get; }
         public Akka.Persistence.Journal.EventAdapters AdaptersFor(string journalPluginId) { }
+        [Akka.Annotations.InternalStableApiAttribute()]
         public Akka.Actor.IActorRef JournalFor(string journalPluginId) { }
         public string PersistenceId(Akka.Actor.IActorRef actor) { }
+        [Akka.Annotations.InternalStableApiAttribute()]
         public Akka.Actor.IActorRef SnapshotStoreFor(string snapshotPluginId) { }
     }
     public sealed class PersistenceSettings : Akka.Actor.Settings
diff --git a/src/core/Akka.Persistence/Persistence.cs b/src/core/Akka.Persistence/Persistence.cs
index 204fd982365..1100b5d0f79 100644
--- a/src/core/Akka.Persistence/Persistence.cs
+++ b/src/core/Akka.Persistence/Persistence.cs
@@ -11,6 +11,7 @@
 using System.Reflection;
 using System.Threading;
 using Akka.Actor;
+using Akka.Annotations;
 using Akka.Configuration;
 using Akka.Event;
 using Akka.Persistence.Journal;
@@ -231,6 +232,7 @@ internal Config ConfigFor(IActorRef journalPluginActor)
         /// This exception is thrown when either the plugin class name is undefined or the configuration path is missing.
         /// </exception>
         /// <returns>TBD</returns>
+        [InternalStableApi]
         public IActorRef JournalFor(string journalPluginId)
         {
             var configPath = string.IsNullOrEmpty(journalPluginId) ? _defaultJournalPluginId.Value : journalPluginId;
@@ -249,6 +251,7 @@ public IActorRef JournalFor(string journalPluginId)
         /// This exception is thrown when either the plugin class name is undefined or the configuration path is missing.
         /// </exception>
         /// <returns>TBD</returns>
+        [InternalStableApi]
         public IActorRef SnapshotStoreFor(string snapshotPluginId)
         {
             var configPath = string.IsNullOrEmpty(snapshotPluginId) ? _defaultSnapshotPluginId.Value : snapshotPluginId;
diff --git a/src/core/Akka/Annotations/Attributes.cs b/src/core/Akka/Annotations/Attributes.cs
index 7f190883852..55c538ddcd5 100644
--- a/src/core/Akka/Annotations/Attributes.cs
+++ b/src/core/Akka/Annotations/Attributes.cs
@@ -11,34 +11,51 @@ namespace Akka.Annotations
 {
     /// <summary>
     /// Marks APIs that are considered internal to Akka and may change at any point in time without any warning.
-    /// 
+    /// <para>
     /// For example, this annotation should be used for code that should be inherently internal, but it cannot be
     /// due to limitations of .NET encapsulation in areas such as inheritance or serialization.
-    /// 
+    /// </para>
+    /// <para>
     /// If a method/class annotated with this method has a xdoc comment, the first line MUST include 
     /// in order to be easily identifiable from generated documentation. Additional information
     /// may be put on the same line as the INTERNAL API comment in order to clarify further.
+    /// </para>
     /// </summary>
     [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Constructor | AttributeTargets.Field | AttributeTargets.Property | AttributeTargets.Method | AttributeTargets.Module, Inherited = true, AllowMultiple = false)]
     public sealed class InternalApiAttribute : Attribute
     {
     }
 
+    /// <summary>
+    /// Marks APIs that are considered internal to Akka and should not be accessed by user code but that are used 
+    /// across Akka project boundaries and therefore shouldn't be changed without considering possible usage 
+    /// outside of the Akka core modules.
+    /// <para>
+    /// If a method/class annotated with this annotation is part of a public API there should be a xdoc comment 
+    /// where the first line MUST include INTERNAL API in order to be easily identifiable from generated documentation. 
+    /// Additional information may be put on the same line as the INTERNAL API comment in order to clarify further.
+    /// </para>
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Constructor | AttributeTargets.Field | AttributeTargets.Property | AttributeTargets.Method | AttributeTargets.Module, Inherited = true, AllowMultiple = false)]
+    public sealed class InternalStableApiAttribute : Attribute
+    {
+    }
+
     /// <summary>
     /// Marks APIs that are meant to evolve towards becoming stable APIs, but are not stable APIs yet.
-    /// 
+    /// <para>
     /// Evolving interfaces MAY change from one patch release to another (i.e. 1.3.0 to 1.3.1) without up-front notice.
     /// A best-effort approach is taken to not cause more breakage than really neccessary, and usual deprecation techniques 
     /// are utilised while evolving these APIs, however there is NO strong guarantee regarding the source or binary 
     /// compatibility of APIs marked using this annotation. 
-    /// 
+    /// </para>
+    /// <para>
     /// It MAY also change when promoting the API to stable, for example such changes may include removal of deprecated 
     /// methods that were introduced during the evolution and final refactoring that were deferred because they would 
     /// have introduced to much breaking changes during the evolution phase. 
-    /// 
-    /// Promoting the API to stable MAY happen in a patch release.
-    /// 
-    /// It is encouraged to document in xmldoc how exactly this API is expected to evolve.
+    /// </para>
+    /// <para>Promoting the API to stable MAY happen in a patch release.</para>
+    /// <para>It is encouraged to document in xmldoc how exactly this API is expected to evolve.</para>
     /// </summary>
     [AttributeUsage(AttributeTargets.Class | AttributeTargets.Struct | AttributeTargets.Enum | AttributeTargets.Interface | AttributeTargets.Constructor | AttributeTargets.Field | AttributeTargets.Property | AttributeTargets.Method | AttributeTargets.Module, Inherited = true, AllowMultiple = false)]
     public sealed class ApiMayChangeAttribute : Attribute
diff --git a/src/core/Akka/Dispatch/SysMsg/ISystemMessage.cs b/src/core/Akka/Dispatch/SysMsg/ISystemMessage.cs
index fcec943c974..78512e63aa3 100644
--- a/src/core/Akka/Dispatch/SysMsg/ISystemMessage.cs
+++ b/src/core/Akka/Dispatch/SysMsg/ISystemMessage.cs
@@ -278,11 +278,12 @@ public interface ISystemMessage : INoSerializationVerificationNeeded
     /// <see cref="ISystemMessage"/> is an interface and too basic to express
     /// all of the capabilities needed to express a full-fledged system message.
     /// </summary>
-    [InternalApi]
+    [InternalStableApi]
     public abstract class SystemMessage : ISystemMessage
     {
         /// <summary>
         /// The next <see cref="ISystemMessage"/> in the linked list.
+        /// Next fields are only modifiable via the <see cref="SystemMessageList"/> class.
         /// </summary>
         [NonSerialized]
         internal SystemMessage Next;
@@ -290,15 +291,12 @@ public abstract class SystemMessage : ISystemMessage
         /// <summary>
         /// Unlinks this message from the linked list.
         /// </summary>
-        public void Unlink()
-        {
-            Next = null;
-        }
+        public void Unlink() => Next = null;
 
         /// <summary>
         /// Returns <c>true</c> if we are unlinked.
         /// </summary>
-        public bool Unlinked { get { return Next == null; } }
+        public bool Unlinked => Next == null;
     }
 
     /// <summary>
diff --git a/src/core/Akka/Util/Option.cs b/src/core/Akka/Util/Option.cs
index 5eb5c24d8d4..d321043ae46 100644
--- a/src/core/Akka/Util/Option.cs
+++ b/src/core/Akka/Util/Option.cs
@@ -8,6 +8,7 @@
 using System;
 using System.Collections.Generic;
 using System.Runtime.CompilerServices;
+using Akka.Annotations;
 
 namespace Akka.Util
 {
@@ -17,6 +18,7 @@ namespace Akka.Util
     /// Useful where distinguishing between null (or zero, or false) and uninitialized is significant.
     /// </summary>
     /// <typeparam name="T">TBD</typeparam>
+    [InternalStableApi]
     public readonly struct Option<T>
     {
         [MethodImpl(MethodImplOptions.AggressiveInlining)]