diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/ack/AckManager.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/ack/AckManager.java
index 32888137..4d560ba5 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/ack/AckManager.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/ack/AckManager.java
@@ -33,12 +33,14 @@
 import com.socketio4j.socketio.MultiTypeAckCallback;
 import com.socketio4j.socketio.MultiTypeArgs;
 import com.socketio4j.socketio.SocketIOClient;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.handler.ClientHead;
 import com.socketio4j.socketio.protocol.Packet;
 import com.socketio4j.socketio.scheduler.CancelableScheduler;
 import com.socketio4j.socketio.scheduler.SchedulerKey;
 import com.socketio4j.socketio.scheduler.SchedulerKey.Type;
 
+@Internal
 public class AckManager implements Disconnectable {
 
     static class AckEntry {
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/ack/AckSchedulerKey.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/ack/AckSchedulerKey.java
index 902097fb..9c6d25d2 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/ack/AckSchedulerKey.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/ack/AckSchedulerKey.java
@@ -18,8 +18,10 @@
 
 import java.util.UUID;
 
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.scheduler.SchedulerKey;
 
+@Internal
 public class AckSchedulerKey extends SchedulerKey {
 
     private final long index;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/AuthorizeHandler.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/AuthorizeHandler.java
index a5e6c884..172649c7 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/AuthorizeHandler.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/AuthorizeHandler.java
@@ -37,6 +37,7 @@
 import com.socketio4j.socketio.SocketIOClient;
 import com.socketio4j.socketio.Transport;
 import com.socketio4j.socketio.ack.AckManager;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.messages.HttpErrorMessage;
 import com.socketio4j.socketio.namespace.Namespace;
 import com.socketio4j.socketio.namespace.NamespacesHub;
@@ -70,6 +71,7 @@
 
 import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
 
+@Internal
 @Sharable
 public class AuthorizeHandler extends ChannelInboundHandlerAdapter implements Disconnectable {
 
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/ClientHead.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/ClientHead.java
index 2799967e..7b05c2b3 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/ClientHead.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/ClientHead.java
@@ -41,6 +41,7 @@
 import com.socketio4j.socketio.HandshakeData;
 import com.socketio4j.socketio.Transport;
 import com.socketio4j.socketio.ack.AckManager;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.messages.OutPacketMessage;
 import com.socketio4j.socketio.namespace.Namespace;
 import com.socketio4j.socketio.protocol.EngineIOVersion;
@@ -60,6 +61,7 @@
 import io.netty.handler.codec.http.HttpHeaderNames;
 import io.netty.util.AttributeKey;
 
+@Internal
 public class ClientHead {
 
     private static final Logger log = LoggerFactory.getLogger(ClientHead.class);
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/ClientsBox.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/ClientsBox.java
index ce8312a3..523df08e 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/ClientsBox.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/ClientsBox.java
@@ -21,9 +21,11 @@
 import java.util.concurrent.ConcurrentHashMap;
 
 import com.socketio4j.socketio.HandshakeData;
+import com.socketio4j.socketio.annotation.Internal;
 
 import io.netty.channel.Channel;
 
+@Internal
 public class ClientsBox {
 
     private final Map<UUID, ClientHead> uuid2clients = new ConcurrentHashMap<>();
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/EncoderHandler.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/EncoderHandler.java
index 151ffd67..8a7b8edf 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/EncoderHandler.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/EncoderHandler.java
@@ -31,6 +31,7 @@
 
 import com.socketio4j.socketio.Configuration;
 import com.socketio4j.socketio.Transport;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.messages.HttpErrorMessage;
 import com.socketio4j.socketio.messages.HttpMessage;
 import com.socketio4j.socketio.messages.OutPacketMessage;
@@ -71,6 +72,7 @@
 
 import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
 
+@Internal
 @Sharable
 public class EncoderHandler extends ChannelOutboundHandlerAdapter {
 
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/InPacketHandler.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/InPacketHandler.java
index 19e1c3f6..d1bed14c 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/InPacketHandler.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/InPacketHandler.java
@@ -23,6 +23,7 @@
 import org.slf4j.LoggerFactory;
 
 import com.socketio4j.socketio.AuthTokenResult;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.listener.ExceptionListener;
 import com.socketio4j.socketio.messages.PacketsMessage;
 import com.socketio4j.socketio.namespace.Namespace;
@@ -40,6 +41,7 @@
 import io.netty.channel.SimpleChannelInboundHandler;
 import io.netty.util.CharsetUtil;
 
+@Internal
 @Sharable
 public class InPacketHandler extends SimpleChannelInboundHandler<PacketsMessage> {
 
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/PacketListener.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/PacketListener.java
index e30970a0..4e0c839a 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/PacketListener.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/PacketListener.java
@@ -22,6 +22,7 @@
 import com.socketio4j.socketio.AckRequest;
 import com.socketio4j.socketio.Transport;
 import com.socketio4j.socketio.ack.AckManager;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.namespace.Namespace;
 import com.socketio4j.socketio.namespace.NamespacesHub;
 import com.socketio4j.socketio.protocol.EngineIOVersion;
@@ -34,6 +35,7 @@
 
 import io.netty.channel.ChannelFuture;
 
+@Internal
 public class PacketListener {
 
     private final NamespacesHub namespacesHub;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/TransportState.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/TransportState.java
index aafe024d..75c12a1b 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/TransportState.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/TransportState.java
@@ -20,10 +20,12 @@
 import java.util.concurrent.ConcurrentLinkedQueue;
 import java.util.concurrent.atomic.AtomicReference;
 
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.protocol.Packet;
 
 import io.netty.channel.Channel;
 
+@Internal
 public class TransportState {
 
     private Queue<Packet> packetsQueue = new ConcurrentLinkedQueue<>();
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/WrongUrlHandler.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/WrongUrlHandler.java
index 335eff52..2809b4f5 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/WrongUrlHandler.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/handler/WrongUrlHandler.java
@@ -19,6 +19,8 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import com.socketio4j.socketio.annotation.Internal;
+
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
@@ -33,6 +35,7 @@
 
 import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
 
+@Internal
 @Sharable
 public class WrongUrlHandler extends ChannelInboundHandlerAdapter {
 
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/HttpErrorMessage.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/HttpErrorMessage.java
index 0c51d71e..8bcee57d 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/HttpErrorMessage.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/HttpErrorMessage.java
@@ -18,6 +18,9 @@
 
 import java.util.Map;
 
+import com.socketio4j.socketio.annotation.Internal;
+
+@Internal
 public class HttpErrorMessage extends HttpMessage {
 
     private final Map<String, Object> data;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/HttpMessage.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/HttpMessage.java
index cdf3580a..11cc5d2b 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/HttpMessage.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/HttpMessage.java
@@ -18,6 +18,9 @@
 
 import java.util.UUID;
 
+import com.socketio4j.socketio.annotation.Internal;
+
+@Internal
 public abstract class HttpMessage {
 
     private final String origin;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/OutPacketMessage.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/OutPacketMessage.java
index c06e8814..6b3783b6 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/OutPacketMessage.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/OutPacketMessage.java
@@ -17,8 +17,10 @@
 package com.socketio4j.socketio.messages;
 
 import com.socketio4j.socketio.Transport;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.handler.ClientHead;
 
+@Internal
 public class OutPacketMessage extends HttpMessage {
 
     private final ClientHead clientHead;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/PacketsMessage.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/PacketsMessage.java
index 7d445c8e..fb550e01 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/PacketsMessage.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/PacketsMessage.java
@@ -17,11 +17,13 @@
 package com.socketio4j.socketio.messages;
 
 import com.socketio4j.socketio.Transport;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.handler.ClientHead;
 
 import io.netty.buffer.ByteBuf;
 import io.netty.util.ReferenceCounted;
 
+@Internal
 public class PacketsMessage implements ReferenceCounted {
 
     private final ClientHead client;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/XHROptionsMessage.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/XHROptionsMessage.java
index cfdad4aa..559d320c 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/XHROptionsMessage.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/XHROptionsMessage.java
@@ -18,6 +18,9 @@
 
 import java.util.UUID;
 
+import com.socketio4j.socketio.annotation.Internal;
+
+@Internal
 public class XHROptionsMessage extends XHRPostMessage {
 
     public XHROptionsMessage(String origin, UUID sessionId) {
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/XHRPostMessage.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/XHRPostMessage.java
index eefde260..d00c81f8 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/XHRPostMessage.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/messages/XHRPostMessage.java
@@ -18,6 +18,9 @@
 
 import java.util.UUID;
 
+import com.socketio4j.socketio.annotation.Internal;
+
+@Internal
 public class XHRPostMessage extends HttpMessage {
 
     public XHRPostMessage(String origin, UUID sessionId) {
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/metrics/NamespaceMeters.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/metrics/NamespaceMeters.java
index d3f32212..4e3d369b 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/metrics/NamespaceMeters.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/metrics/NamespaceMeters.java
@@ -21,6 +21,8 @@
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.concurrent.atomic.AtomicReference;
 
+import com.socketio4j.socketio.annotation.Internal;
+
 import io.micrometer.core.instrument.Counter;
 import io.micrometer.core.instrument.Gauge;
 import io.micrometer.core.instrument.MeterRegistry;
@@ -38,6 +40,7 @@
  * @author https://github.com/sanjomo
  * @date 05/01/26 3:10 pm
  */
+@Internal
 public final class NamespaceMeters {
 
     /* ===================== Event Counters ===================== */
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/CompositeIterable.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/CompositeIterable.java
index 3dd003da..937204cf 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/CompositeIterable.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/CompositeIterable.java
@@ -20,6 +20,9 @@
 import java.util.Iterator;
 import java.util.List;
 
+import com.socketio4j.socketio.annotation.Internal;
+
+@Internal
 public class CompositeIterable<T> implements Iterable<T> {
 
     private List<Iterable<T>> iterablesList;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/CompositeIterator.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/CompositeIterator.java
index 74c2eed0..cecbaa4e 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/CompositeIterator.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/CompositeIterator.java
@@ -18,6 +18,9 @@
 
 import java.util.Iterator;
 
+import com.socketio4j.socketio.annotation.Internal;
+
+@Internal
 public class CompositeIterator<T> implements Iterator<T> {
 
     private final Iterator<Iterator<T>> listIterator;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/IterableCollection.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/IterableCollection.java
index 6178ee1f..09ad9044 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/IterableCollection.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/misc/IterableCollection.java
@@ -19,6 +19,9 @@
 import java.util.AbstractCollection;
 import java.util.Iterator;
 
+import com.socketio4j.socketio.annotation.Internal;
+
+@Internal
 public class IterableCollection<T> extends AbstractCollection<T> {
 
     private final CompositeIterable<T> iterable;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/EventEntry.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/EventEntry.java
index 74df8cbc..d70d932d 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/EventEntry.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/EventEntry.java
@@ -19,8 +19,10 @@
 import java.util.Queue;
 import java.util.concurrent.ConcurrentLinkedQueue;
 
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.listener.DataListener;
 
+@Internal
 public class EventEntry<T> {
 
     private final Queue<DataListener<T>> listeners = new ConcurrentLinkedQueue<DataListener<T>>();
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/Namespace.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/Namespace.java
index 6aebfee7..d5a9236d 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/Namespace.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/Namespace.java
@@ -45,6 +45,7 @@
 import com.socketio4j.socketio.SingleRoomBroadcastOperations;
 import com.socketio4j.socketio.SocketIOClient;
 import com.socketio4j.socketio.SocketIONamespace;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.annotation.ScannerEngine;
 import com.socketio4j.socketio.listener.CatchAllEventListener;
 import com.socketio4j.socketio.listener.ConnectListener;
@@ -66,13 +67,13 @@
 import com.socketio4j.socketio.store.event.LeaveMessage;
 import com.socketio4j.socketio.transport.NamespaceClient;
 
-
 /**
  * Hub object for all clients in one namespace.
  * Namespace shares by different namespace-clients.
  *
  * @see com.socketio4j.socketio.transport.NamespaceClient
  */
+@Internal
 public class Namespace implements SocketIONamespace {
 
     private static final Logger log = LoggerFactory.getLogger(Namespace.class);
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/NamespacesHub.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/NamespacesHub.java
index ccb96d58..1a902fb9 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/NamespacesHub.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/namespace/NamespacesHub.java
@@ -25,8 +25,10 @@
 import com.socketio4j.socketio.Configuration;
 import com.socketio4j.socketio.SocketIOClient;
 import com.socketio4j.socketio.SocketIONamespace;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.misc.CompositeIterable;
 
+@Internal
 public class NamespacesHub {
 
     private final ConcurrentMap<String, SocketIONamespace> namespaces = new ConcurrentHashMap<>();
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/AuthPacket.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/AuthPacket.java
index 21dc908e..ace3a9f6 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/AuthPacket.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/AuthPacket.java
@@ -18,7 +18,9 @@
 
 import java.util.UUID;
 
+import com.socketio4j.socketio.annotation.Internal;
 
+@Internal
 public class AuthPacket {
 
     private final UUID sid;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/ConnPacket.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/ConnPacket.java
index 34d56271..e062d2d1 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/ConnPacket.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/ConnPacket.java
@@ -18,6 +18,9 @@
 
 import java.util.UUID;
 
+import com.socketio4j.socketio.annotation.Internal;
+
+@Internal
 public class ConnPacket {
 
     private final UUID sid;
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/EngineIOVersion.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/EngineIOVersion.java
index ad282049..77b43b50 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/EngineIOVersion.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/EngineIOVersion.java
@@ -19,12 +19,9 @@
 import java.util.HashMap;
 import java.util.Map;
 
-import com.socketio4j.socketio.annotation.Internal;
-
 /**
  * Engine.IO protocol version
  */
-@Internal
 public enum EngineIOVersion {
     /**
      * @link <a href="https://github.com/socketio/engine.io-protocol/tree/v2">Engine.IO version 2</a>
@@ -38,7 +35,13 @@ public enum EngineIOVersion {
      * current version
      * @link <a href="https://github.com/socketio/engine.io-protocol/tree/main">Engine.IO version 4</a>
      */
-    V4("4");
+    V4("4"),
+
+    /**
+     * @deprecated Unknown revisions are rejected in handshake; use {@link #isSupported(String)}
+     */
+    @Deprecated
+    UNKNOWN("");
 
     public static final String EIO = "EIO";
 
@@ -46,7 +49,9 @@ public enum EngineIOVersion {
 
     static {
         for (EngineIOVersion value : values()) {
-            VERSIONS.put(value.getValue(), value);
+            if (value != UNKNOWN) {
+                VERSIONS.put(value.getValue(), value);
+            }
         }
     }
 
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/Packet.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/Packet.java
index 53917113..0a0d8c06 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/Packet.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/Packet.java
@@ -21,17 +21,17 @@
 import java.util.Collections;
 import java.util.List;
 
-import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.namespace.Namespace;
 
 import io.netty.buffer.ByteBuf;
 
-@Internal
 public class Packet implements Serializable {
 
     private static final long serialVersionUID = 4560159536486711426L;
 
     private PacketType type;
+    @Deprecated
+    private EngineIOVersion engineIOVersion = EngineIOVersion.V4;
 
     private PacketType subType;
     private Long ackId;
@@ -40,6 +40,8 @@ public class Packet implements Serializable {
 
     private Object data;
 
+    @Deprecated
+    private transient ByteBuf dataSource;
     private int attachmentsCount;
     private List<ByteBuf> attachments = Collections.emptyList();
 
@@ -52,6 +54,15 @@ public Packet(PacketType type) {
         this.type = type;
     }
 
+    /**
+     * @deprecated Engine.IO version is now negotiated per-connection. Use {@link #Packet(PacketType)} instead.
+     */
+    @Deprecated
+    public Packet(PacketType type, EngineIOVersion engineIOVersion) {
+        this(type);
+        this.engineIOVersion = engineIOVersion;
+    }
+
     public PacketType getSubType() {
         return subType;
     }
@@ -88,7 +99,6 @@ public <T> T getData() {
      * Otherwise, returns original object unchanged
      *
      * @param namespace
-     * @param engineIOVersion
      * @return packet
      */
     public Packet withNsp(String namespace) {
@@ -98,6 +108,34 @@ public Packet withNsp(String namespace) {
             Packet newPacket = new Packet(this.type);
             newPacket.setAckId(this.ackId);
             newPacket.setData(this.data);
+            newPacket.setDataSource(this.dataSource);
+            newPacket.setName(this.name);
+            newPacket.setSubType(this.subType);
+            newPacket.setNsp(namespace);
+            newPacket.setEngineIOVersion(this.engineIOVersion);
+            newPacket.attachments = this.attachments;
+            newPacket.attachmentsCount = this.attachmentsCount;
+            return newPacket;
+        }
+    }
+
+    /**
+     * Creates a copy of #{@link Packet} with new namespace set.
+     *
+     * @deprecated Engine.IO version is now negotiated per-connection. Use {@link #withNsp(String)} instead.
+     * @param namespace
+     * @param engineIOVersion
+     * @return packet
+     */
+    @Deprecated
+    public Packet withNsp(String namespace, EngineIOVersion engineIOVersion) {
+        if (this.nsp.equalsIgnoreCase(namespace)) {
+            return this;
+        } else {
+            Packet newPacket = new Packet(this.type, engineIOVersion);
+            newPacket.setAckId(this.ackId);
+            newPacket.setData(this.data);
+            newPacket.setDataSource(this.dataSource);
             newPacket.setName(this.name);
             newPacket.setSubType(this.subType);
             newPacket.setNsp(namespace);
@@ -156,6 +194,37 @@ public boolean hasAttachments() {
     public boolean isAttachmentsLoaded() {
         return this.attachments.size() == attachmentsCount;
     }
+    /**
+     * @deprecated Engine.IO version is now negotiated per-connection.
+     */
+    @Deprecated
+    public EngineIOVersion getEngineIOVersion() {
+        return engineIOVersion;
+    }
+
+    /**
+     * @deprecated Engine.IO version is now negotiated per-connection.
+     */
+    @Deprecated
+    public void setEngineIOVersion(EngineIOVersion engineIOVersion) {
+        this.engineIOVersion = engineIOVersion;
+    }
+
+    /**
+     * @deprecated Binary attachments are handled via {@link #getAttachments()}.
+     */
+    @Deprecated
+    public ByteBuf getDataSource() {
+        return dataSource;
+    }
+
+    /**
+     * @deprecated Binary attachments are handled via {@link #addAttachment(ByteBuf)}.
+     */
+    @Deprecated
+    public void setDataSource(ByteBuf dataSource) {
+        this.dataSource = dataSource;
+    }
 
     @Override
     public String toString() {
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/PacketType.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/PacketType.java
index 718c3c72..bb3423bb 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/PacketType.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/PacketType.java
@@ -17,9 +17,6 @@
 package com.socketio4j.socketio.protocol;
 
 
-import com.socketio4j.socketio.annotation.Internal;
-
-@Internal
 public enum PacketType {
 
     OPEN(0), CLOSE(1), PING(2), PONG(3), MESSAGE(4), UPGRADE(5), NOOP(6),
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/UTF8CharsScanner.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/UTF8CharsScanner.java
index 7d1ecc82..89fb0e21 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/UTF8CharsScanner.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/protocol/UTF8CharsScanner.java
@@ -16,8 +16,11 @@
  */
 package com.socketio4j.socketio.protocol;
 
+import com.socketio4j.socketio.annotation.Internal;
+
 import io.netty.buffer.ByteBuf;
 
+@Internal
 public class UTF8CharsScanner {
 
     /**
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/CancelableScheduler.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/CancelableScheduler.java
index 1accc102..d35eb7ab 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/CancelableScheduler.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/CancelableScheduler.java
@@ -18,8 +18,11 @@
 
 import java.util.concurrent.TimeUnit;
 
+import com.socketio4j.socketio.annotation.Internal;
+
 import io.netty.channel.ChannelHandlerContext;
 
+@Internal
 public interface CancelableScheduler {
 
     void update(ChannelHandlerContext ctx);
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/HashedWheelScheduler.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/HashedWheelScheduler.java
index b0ce4000..7d0bef3e 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/HashedWheelScheduler.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/HashedWheelScheduler.java
@@ -21,10 +21,13 @@
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 
+import com.socketio4j.socketio.annotation.Internal;
+
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.util.HashedWheelTimer;
 import io.netty.util.Timeout;
 
+@Internal
 public class HashedWheelScheduler implements CancelableScheduler {
 
     private final Map<SchedulerKey, Timeout> scheduledFutures = new ConcurrentHashMap<>();
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/HashedWheelTimeoutScheduler.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/HashedWheelTimeoutScheduler.java
index 93242e9b..aba289fa 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/HashedWheelTimeoutScheduler.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/HashedWheelTimeoutScheduler.java
@@ -30,11 +30,13 @@
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 
+import com.socketio4j.socketio.annotation.Internal;
+
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.util.HashedWheelTimer;
 import io.netty.util.Timeout;
 
-
+@Internal
 public class HashedWheelTimeoutScheduler implements CancelableScheduler {
 
     private final ConcurrentMap<SchedulerKey, Timeout> scheduledFutures = new ConcurrentHashMap<>();
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/SchedulerKey.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/SchedulerKey.java
index b5239cb0..ce0b9e23 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/SchedulerKey.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/scheduler/SchedulerKey.java
@@ -17,6 +17,9 @@
 package com.socketio4j.socketio.scheduler;
 
 
+import com.socketio4j.socketio.annotation.Internal;
+
+@Internal
 public class SchedulerKey {
 
     public enum Type {PING, PING_TIMEOUT, ACK_TIMEOUT, UPGRADE_TIMEOUT, POLL_FLUSH_TIMEOUT};
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/store/event/EventMessageJsonSupport.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/store/event/EventMessageJsonSupport.java
index d146ed29..bfc9f3aa 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/store/event/EventMessageJsonSupport.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/store/event/EventMessageJsonSupport.java
@@ -39,12 +39,14 @@
 import com.fasterxml.jackson.databind.deser.std.UntypedObjectDeserializer;
 import com.fasterxml.jackson.databind.json.JsonMapper;
 import com.fasterxml.jackson.databind.module.SimpleModule;
+import com.socketio4j.socketio.annotation.Internal;
 
 /**
  * Shared JSON ObjectMapper builder for JSON-based EventStores (NATS, Kafka, Redis Streams, etc.).
  * Guarantees lossless JSON serialization and deserialization of binary byte arrays (byte[])
  * embedded inside EventMessages and Packets.
  */
+@Internal
 public final class EventMessageJsonSupport {
     private static final String BYTES_FIELD = "$bytes";
     private EventMessageJsonSupport() {
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/transport/PollingTransport.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/transport/PollingTransport.java
index e335207d..95e85c3a 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/transport/PollingTransport.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/transport/PollingTransport.java
@@ -27,6 +27,7 @@
 import org.slf4j.LoggerFactory;
 
 import com.socketio4j.socketio.Transport;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.handler.AuthorizeHandler;
 import com.socketio4j.socketio.handler.ClientHead;
 import com.socketio4j.socketio.handler.ClientsBox;
@@ -53,6 +54,7 @@
 import io.netty.handler.codec.http.QueryStringDecoder;
 import io.netty.handler.codec.http.websocketx.WebSocket13FrameDecoder;
 
+@Internal
 @Sharable
 public class PollingTransport extends ChannelInboundHandlerAdapter {
 
diff --git a/netty-socketio-core/src/main/java/com/socketio4j/socketio/transport/WebSocketTransport.java b/netty-socketio-core/src/main/java/com/socketio4j/socketio/transport/WebSocketTransport.java
index e39e54db..ee8a7d11 100644
--- a/netty-socketio-core/src/main/java/com/socketio4j/socketio/transport/WebSocketTransport.java
+++ b/netty-socketio-core/src/main/java/com/socketio4j/socketio/transport/WebSocketTransport.java
@@ -26,6 +26,7 @@
 import com.socketio4j.socketio.Configuration;
 import com.socketio4j.socketio.SocketIOChannelInitializer;
 import com.socketio4j.socketio.Transport;
+import com.socketio4j.socketio.annotation.Internal;
 import com.socketio4j.socketio.handler.AuthorizeHandler;
 import com.socketio4j.socketio.handler.ClientHead;
 import com.socketio4j.socketio.handler.ClientsBox;
@@ -64,6 +65,7 @@
 
 import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
 
+@Internal
 @Sharable
 public class WebSocketTransport extends ChannelInboundHandlerAdapter {
 
diff --git a/netty-socketio-core/src/test/java/com/socketio4j/socketio/protocol/PacketTest.java b/netty-socketio-core/src/test/java/com/socketio4j/socketio/protocol/PacketTest.java
index b69d513d..eb738657 100644
--- a/netty-socketio-core/src/test/java/com/socketio4j/socketio/protocol/PacketTest.java
+++ b/netty-socketio-core/src/test/java/com/socketio4j/socketio/protocol/PacketTest.java
@@ -71,9 +71,16 @@ public void testPacketConstructorWithType() {
 
     @Test
     public void testPacketConstructorWithTypeAndEngineIOVersion() {
-        Packet packet = new Packet(PacketType.EVENT);
-        assertEquals(PacketType.EVENT, packet.getType());
-        // assertEquals(EngineIOVersion.V4, packet.getEngineIOVersion());
+        Packet packetDefault = new Packet(PacketType.EVENT);
+        assertEquals(PacketType.EVENT, packetDefault.getType());
+        assertEquals(EngineIOVersion.V4, packetDefault.getEngineIOVersion());
+
+        Packet packetV3 = new Packet(PacketType.EVENT, EngineIOVersion.V3);
+        assertEquals(PacketType.EVENT, packetV3.getType());
+        assertEquals(EngineIOVersion.V3, packetV3.getEngineIOVersion());
+
+        packetV3.setEngineIOVersion(EngineIOVersion.V4);
+        assertEquals(EngineIOVersion.V4, packetV3.getEngineIOVersion());
     }
 
     @Test
@@ -191,18 +198,18 @@ public void testPacketWithAllFields() {
         packet.setData("testData");
         packet.setAckId(456L);
         packet.setNsp("/test");
-        // packet.setDataSource(Unpooled.wrappedBuffer("source".getBytes()));
+        packet.setDataSource(Unpooled.wrappedBuffer("source".getBytes()));
         packet.initAttachments(1);
         packet.addAttachment(Unpooled.wrappedBuffer("attachment".getBytes()));
         
         assertEquals(PacketType.MESSAGE, packet.getType());
-        // assertEquals(EngineIOVersion.V4, packet.getEngineIOVersion());
+        assertEquals(EngineIOVersion.V4, packet.getEngineIOVersion());
         assertEquals(PacketType.EVENT, packet.getSubType());
         assertEquals("testEvent", packet.getName());
         assertEquals("testData", packet.getData());
         assertEquals(Long.valueOf(456), packet.getAckId());
         assertEquals("/test", packet.getNsp());
-        // assertNotNull(packet.getDataSource());
+        assertNotNull(packet.getDataSource());
         assertTrue(packet.hasAttachments());
         assertTrue(packet.isAttachmentsLoaded());
         assertEquals(1, packet.getAttachments().size());
@@ -226,7 +233,8 @@ public void testPacketCopyWithDifferentNamespace() {
         Object copiedData = copiedPacket.getData();
         assertEquals(originalData, copiedData);
         assertSame(originalPacket.getAttachments(), copiedPacket.getAttachments());
-        // assertSame(originalPacket.getDataSource(), copiedPacket.getDataSource());
+        assertSame(originalPacket.getDataSource(), copiedPacket.getDataSource());
+        assertEquals(originalPacket.getEngineIOVersion(), copiedPacket.getEngineIOVersion());
     }
 
     @Test
@@ -251,7 +259,8 @@ private void assertPacketCopied(Packet oldPacket, Packet newPacket) {
         Object oldData = oldPacket.getData();
         Object newData = newPacket.getData();
         assertEquals(oldData, newData);
-        // assertSame(oldPacket.getDataSource(), newPacket.getDataSource());
+        assertSame(oldPacket.getDataSource(), newPacket.getDataSource());
+        assertEquals(oldPacket.getEngineIOVersion(), newPacket.getEngineIOVersion());
     }
 
     private Packet createPacket() {
@@ -261,9 +270,22 @@ private Packet createPacket() {
         packet.setData("data");
         packet.setAckId(1L);
         packet.setNsp("old");
-        // packet.setDataSource(Unpooled.wrappedBuffer(new byte[]{10}));
+        packet.setDataSource(Unpooled.wrappedBuffer(new byte[]{10}));
         packet.initAttachments(1);
         packet.addAttachment(Unpooled.wrappedBuffer(new byte[]{20}));
         return packet;
     }
+
+    @Test
+    public void testPacketCopyWithDifferentNamespaceAndEngineIOVersion() {
+        Packet originalPacket = createPacket();
+        String newNamespace = "/newNamespace";
+
+        Packet copiedPacket = originalPacket.withNsp(newNamespace, EngineIOVersion.V3);
+
+        assertEquals(newNamespace, copiedPacket.getNsp());
+        assertNotSame(originalPacket, copiedPacket);
+        assertEquals(EngineIOVersion.V3, copiedPacket.getEngineIOVersion());
+        assertSame(originalPacket.getDataSource(), copiedPacket.getDataSource());
+    }
 }
\ No newline at end of file
diff --git a/pom.xml b/pom.xml
index 1209a3ca..67d171ec 100644
--- a/pom.xml
+++ b/pom.xml
@@ -91,7 +91,12 @@
     <lz4.version>1.10.3</lz4.version>
     <okhttp.version>3.12.13</okhttp.version>
     <socketio.test.forkCount>1</socketio.test.forkCount>
-
+    <revapi-maven-plugin.version>0.15.1</revapi-maven-plugin.version>
+    <revapi-java.version>0.28.4</revapi-java.version>
+    <revapi.oldVersion>4.0.1</revapi.oldVersion>
+    <revapi.skip>false</revapi.skip>
+    <revapi.failOnUnresolvedArtifacts>false</revapi.failOnUnresolvedArtifacts>
+    <revapi.failCriticality>error</revapi.failCriticality>
   </properties>
 
   <profiles>
@@ -692,6 +697,102 @@
           </execution>
         </executions>
       </plugin>
+
+      <plugin>
+        <groupId>org.revapi</groupId>
+        <artifactId>revapi-maven-plugin</artifactId>
+        <version>${revapi-maven-plugin.version}</version>
+        <dependencies>
+          <dependency>
+            <groupId>org.revapi</groupId>
+            <artifactId>revapi-java</artifactId>
+            <version>${revapi-java.version}</version>
+          </dependency>
+        </dependencies>
+        <configuration>
+          <oldVersion>${revapi.oldVersion}</oldVersion>
+          <skip>${revapi.skip}</skip>
+          <checkDependencies>false</checkDependencies>
+          <failCriticality>${revapi.failCriticality}</failCriticality>
+          <failOnUnresolvedArtifacts>${revapi.failOnUnresolvedArtifacts}</failOnUnresolvedArtifacts>
+          <analysisConfiguration>
+            [
+              {
+                "extension": "revapi.java",
+                "configuration": {
+                  "missing-classes": {
+                    "behavior": "ignore"
+                  }
+                }
+              },
+              {
+                "extension": "revapi.filter",
+                "configuration": {
+                  "elements": {
+                    "exclude": [
+                      {
+                        "matcher": "java",
+                        "match": "@com.socketio4j.socketio.annotation.Internal ^*;"
+                      }
+                    ]
+                  }
+                }
+              },
+              {
+                "extension": "revapi.differences",
+                "configuration": {
+                  "ignore": true,
+                  "differences": [
+                    {
+                      "code": "java.class.removed",
+                      "regex": true,
+                      "old": "(class|interface) com\\.socketio4j\\.socketio\\.(ack\\.(AckManager|AckSchedulerKey)|handler\\.(AuthorizeHandler|ClientHead|ClientsBox|EncoderHandler|InPacketHandler|PacketListener|TransportState|WrongUrlHandler)|messages\\.(HttpErrorMessage|HttpMessage|OutPacketMessage|PacketsMessage|XHROptionsMessage|XHRPostMessage)|metrics\\.NamespaceMeters|misc\\.(CompositeIterable.*|CompositeIterator.*|IterableCollection.*)|namespace\\.(EventEntry.*|Namespace|NamespacesHub)|protocol\\.(AuthPacket|ConnPacket|Event|PacketDecoder|PacketEncoder|UTF8CharsScanner)|scheduler\\.(CancelableScheduler|HashedWheelScheduler|HashedWheelTimeoutScheduler|SchedulerKey)|store\\.event\\.EventMessageJsonSupport|transport\\.(PollingTransport|WebSocketTransport))",
+                      "justification": "Transitioned specific internal implementation classes to @Internal to establish API boundaries"
+                    },
+                    {
+                      "code": "java.annotation.added",
+                      "annotation": "@org.jetbrains.annotations.Nullable",
+                      "justification": "Added nullability annotations for enhanced type safety and Kotlin interop"
+                    },
+                    {
+                      "code": "java.method.exception.checkedRemoved",
+                      "justification": "Removing checked Exception makes listener methods easier to implement without boilerplate throws clause"
+                    },
+                    {
+                      "code": "java.method.removed",
+                      "old": "method void com.socketio4j.socketio.handler.ClientHead::setLastBinaryPacket(com.socketio4j.socketio.protocol.Packet)",
+                      "justification": "Internal binary packet handling moved to dedicated pipeline handler"
+                    },
+                    {
+                      "code": "java.method.addedToInterface",
+                      "new": "method void com.socketio4j.socketio.listener.ClientListeners::removeConnectListener(com.socketio4j.socketio.listener.ConnectListener)",
+                      "justification": "Added default method to allow dynamic unregistering of connect listeners"
+                    },
+                    {
+                      "code": "java.method.addedToInterface",
+                      "new": "method void com.socketio4j.socketio.listener.ClientListeners::removeDisconnectListener(com.socketio4j.socketio.listener.DisconnectListener)",
+                      "justification": "Added default method to allow dynamic unregistering of disconnect listeners"
+                    },
+                    {
+                      "code": "java.field.serialVersionUIDUnchanged",
+                      "old": "field com.socketio4j.socketio.protocol.Packet.serialVersionUID",
+                      "justification": "Packet serialization schema evolved; serialVersionUID maintained for backwards compatibility"
+                    }
+                  ]
+                }
+              }
+            ]
+          </analysisConfiguration>
+        </configuration>
+        <executions>
+          <execution>
+            <id>check-api</id>
+            <goals>
+              <goal>check</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>
 </project>