diff --git a/framework/src/android/net/DnsResolverServiceManager.java b/framework/src/android/net/DnsResolverServiceManager.java
index 79009e8..e64d2ae 100644
--- a/framework/src/android/net/DnsResolverServiceManager.java
+++ b/framework/src/android/net/DnsResolverServiceManager.java
@@ -29,7 +29,7 @@
 
     private final IBinder mResolver;
 
-    DnsResolverServiceManager(IBinder resolver) {
+    public DnsResolverServiceManager(IBinder resolver) {
         mResolver = resolver;
     }
 
diff --git a/framework/src/android/net/NattSocketKeepalive.java b/framework/src/android/net/NattSocketKeepalive.java
index a15d165..56cc923 100644
--- a/framework/src/android/net/NattSocketKeepalive.java
+++ b/framework/src/android/net/NattSocketKeepalive.java
@@ -33,7 +33,7 @@
     @NonNull private final InetAddress mDestination;
     private final int mResourceId;
 
-    NattSocketKeepalive(@NonNull IConnectivityManager service,
+    public NattSocketKeepalive(@NonNull IConnectivityManager service,
             @NonNull Network network,
             @NonNull ParcelFileDescriptor pfd,
             int resourceId,
@@ -48,7 +48,7 @@
     }
 
     @Override
-    void startImpl(int intervalSec) {
+    protected void startImpl(int intervalSec) {
         mExecutor.execute(() -> {
             try {
                 mService.startNattKeepaliveWithFd(mNetwork, mPfd, mResourceId,
@@ -62,7 +62,7 @@
     }
 
     @Override
-    void stopImpl() {
+    protected void stopImpl() {
         mExecutor.execute(() -> {
             try {
                 if (mSlot != null) {
diff --git a/framework/src/android/net/QosCallbackConnection.java b/framework/src/android/net/QosCallbackConnection.java
index de0fc24..cfceddd 100644
--- a/framework/src/android/net/QosCallbackConnection.java
+++ b/framework/src/android/net/QosCallbackConnection.java
@@ -35,7 +35,7 @@
  *
  * @hide
  */
-class QosCallbackConnection extends android.net.IQosCallback.Stub {
+public class QosCallbackConnection extends android.net.IQosCallback.Stub {
 
     @NonNull private final ConnectivityManager mConnectivityManager;
     @Nullable private volatile QosCallback mCallback;
@@ -56,7 +56,7 @@
      *                 {@link Executor} must run callback sequentially, otherwise the order of
      *                 callbacks cannot be guaranteed.
      */
-    QosCallbackConnection(@NonNull final ConnectivityManager connectivityManager,
+    public QosCallbackConnection(@NonNull final ConnectivityManager connectivityManager,
             @NonNull final QosCallback callback,
             @NonNull final Executor executor) {
         mConnectivityManager = Objects.requireNonNull(connectivityManager,
@@ -142,7 +142,7 @@
      * There are no synchronization guarantees on exactly when the callback will stop receiving
      * messages.
      */
-    void stopReceivingMessages() {
+    public void stopReceivingMessages() {
         mCallback = null;
     }
 }
diff --git a/framework/src/android/net/QosCallbackException.java b/framework/src/android/net/QosCallbackException.java
index b80cff4..9e5d98a 100644
--- a/framework/src/android/net/QosCallbackException.java
+++ b/framework/src/android/net/QosCallbackException.java
@@ -85,7 +85,7 @@
      * {@hide}
      */
     @NonNull
-    static QosCallbackException createException(@ExceptionType final int type) {
+    public static QosCallbackException createException(@ExceptionType final int type) {
         switch (type) {
             case EX_TYPE_FILTER_NETWORK_RELEASED:
                 return new QosCallbackException(new NetworkReleasedException());
diff --git a/framework/src/android/net/QosFilter.java b/framework/src/android/net/QosFilter.java
index b432644..01dc4bb 100644
--- a/framework/src/android/net/QosFilter.java
+++ b/framework/src/android/net/QosFilter.java
@@ -33,13 +33,15 @@
 @SystemApi
 public abstract class QosFilter {
 
-    /**
-     * The constructor is kept hidden from outside this package to ensure that all derived types
-     * are known and properly handled when being passed to and from {@link NetworkAgent}.
-     *
-     * @hide
-     */
-    QosFilter() {
+    /** @hide */
+    protected QosFilter() {
+        // Ensure that all derived types are known, and known to be properly handled when being
+        // passed to and from NetworkAgent.
+        // For now the only known derived type is QosSocketFilter.
+        if (!(this instanceof QosSocketFilter)) {
+            throw new UnsupportedOperationException(
+                    "Unsupported QosFilter type: " + this.getClass().getName());
+        }
     }
 
     /**
diff --git a/framework/src/android/net/QosSocketInfo.java b/framework/src/android/net/QosSocketInfo.java
index 49ac22b..da9b356 100644
--- a/framework/src/android/net/QosSocketInfo.java
+++ b/framework/src/android/net/QosSocketInfo.java
@@ -73,9 +73,10 @@
      * The parcel file descriptor wrapped around the socket's file descriptor.
      *
      * @return the parcel file descriptor of the socket
+     * @hide
      */
     @NonNull
-    ParcelFileDescriptor getParcelFileDescriptor() {
+    public ParcelFileDescriptor getParcelFileDescriptor() {
         return mParcelFileDescriptor;
     }
 
diff --git a/framework/src/android/net/SocketKeepalive.java b/framework/src/android/net/SocketKeepalive.java
index f6cae72..57cf5e3 100644
--- a/framework/src/android/net/SocketKeepalive.java
+++ b/framework/src/android/net/SocketKeepalive.java
@@ -52,7 +52,8 @@
  * request. If it does, it MUST support at least 3 concurrent keepalive slots.
  */
 public abstract class SocketKeepalive implements AutoCloseable {
-    static final String TAG = "SocketKeepalive";
+    /** @hide */
+    protected static final String TAG = "SocketKeepalive";
 
     /**
      * Success. It indicates there is no error.
@@ -215,15 +216,22 @@
         }
     }
 
-    @NonNull final IConnectivityManager mService;
-    @NonNull final Network mNetwork;
-    @NonNull final ParcelFileDescriptor mPfd;
-    @NonNull final Executor mExecutor;
-    @NonNull final ISocketKeepaliveCallback mCallback;
+    /** @hide */
+    @NonNull protected final IConnectivityManager mService;
+    /** @hide */
+    @NonNull protected final Network mNetwork;
+    /** @hide */
+    @NonNull protected final ParcelFileDescriptor mPfd;
+    /** @hide */
+    @NonNull protected final Executor mExecutor;
+    /** @hide */
+    @NonNull protected final ISocketKeepaliveCallback mCallback;
     // TODO: remove slot since mCallback could be used to identify which keepalive to stop.
-    @Nullable Integer mSlot;
+    /** @hide */
+    @Nullable protected Integer mSlot;
 
-    SocketKeepalive(@NonNull IConnectivityManager service, @NonNull Network network,
+    /** @hide */
+    public SocketKeepalive(@NonNull IConnectivityManager service, @NonNull Network network,
             @NonNull ParcelFileDescriptor pfd,
             @NonNull Executor executor, @NonNull Callback callback) {
         mService = service;
@@ -303,7 +311,8 @@
         startImpl(intervalSec);
     }
 
-    abstract void startImpl(int intervalSec);
+    /** @hide */
+    protected abstract void startImpl(int intervalSec);
 
     /**
      * Requests that keepalive be stopped. The application must wait for {@link Callback#onStopped}
@@ -313,7 +322,8 @@
         stopImpl();
     }
 
-    abstract void stopImpl();
+    /** @hide */
+    protected abstract void stopImpl();
 
     /**
      * Deactivate this {@link SocketKeepalive} and free allocated resources. The instance won't be
diff --git a/framework/src/android/net/TcpSocketKeepalive.java b/framework/src/android/net/TcpSocketKeepalive.java
index d89814d..7131784 100644
--- a/framework/src/android/net/TcpSocketKeepalive.java
+++ b/framework/src/android/net/TcpSocketKeepalive.java
@@ -24,9 +24,9 @@
 import java.util.concurrent.Executor;
 
 /** @hide */
-final class TcpSocketKeepalive extends SocketKeepalive {
+public final class TcpSocketKeepalive extends SocketKeepalive {
 
-    TcpSocketKeepalive(@NonNull IConnectivityManager service,
+    public TcpSocketKeepalive(@NonNull IConnectivityManager service,
             @NonNull Network network,
             @NonNull ParcelFileDescriptor pfd,
             @NonNull Executor executor,
@@ -50,7 +50,7 @@
      *   acknowledgement.
      */
     @Override
-    void startImpl(int intervalSec) {
+    protected void startImpl(int intervalSec) {
         mExecutor.execute(() -> {
             try {
                 mService.startTcpKeepalive(mNetwork, mPfd, intervalSec, mCallback);
@@ -62,7 +62,7 @@
     }
 
     @Override
-    void stopImpl() {
+    protected void stopImpl() {
         mExecutor.execute(() -> {
             try {
                 if (mSlot != null) {