diff --git a/framework/api/system-current.txt b/framework/api/system-current.txt
index 703fca408f..c19fcdd2a7 100644
--- a/framework/api/system-current.txt
+++ b/framework/api/system-current.txt
@@ -216,6 +216,7 @@ package android.net {
     method public void markConnected();
     method public void onAddKeepalivePacketFilter(int, @NonNull android.net.KeepalivePacketData);
     method public void onAutomaticReconnectDisabled();
+    method public void onBandwidthUpdateRequested();
     method public void onNetworkUnwanted();
     method public void onQosCallbackRegistered(int, @NonNull android.net.QosFilter);
     method public void onQosCallbackUnregistered(int);
@@ -233,6 +234,7 @@ package android.net {
     method public final void sendQosSessionAvailable(int, int, @NonNull android.telephony.data.EpsBearerQosSessionAttributes);
     method public final void sendQosSessionLost(int, int);
     method public final void sendSocketKeepaliveEvent(int, int);
+    method @Deprecated public void setLegacySubtype(int, @NonNull String);
     method public final void setUnderlyingNetworks(@Nullable java.util.List<android.net.Network>);
     method public void unregister();
     field public static final int VALIDATION_STATUS_NOT_VALID = 2; // 0x2
@@ -253,7 +255,12 @@ package android.net {
   public static final class NetworkAgentConfig.Builder {
     ctor public NetworkAgentConfig.Builder();
     method @NonNull public android.net.NetworkAgentConfig build();
+    method @NonNull public android.net.NetworkAgentConfig.Builder disableNat64Detection();
+    method @NonNull public android.net.NetworkAgentConfig.Builder disableProvisioningNotification();
     method @NonNull public android.net.NetworkAgentConfig.Builder setExplicitlySelected(boolean);
+    method @NonNull public android.net.NetworkAgentConfig.Builder setLegacyExtraInfo(@NonNull String);
+    method @NonNull public android.net.NetworkAgentConfig.Builder setLegacySubType(int);
+    method @NonNull public android.net.NetworkAgentConfig.Builder setLegacySubTypeName(@NonNull String);
     method @NonNull public android.net.NetworkAgentConfig.Builder setLegacyType(int);
     method @NonNull public android.net.NetworkAgentConfig.Builder setLegacyTypeName(@NonNull String);
     method @NonNull public android.net.NetworkAgentConfig.Builder setPartialConnectivityAcceptable(boolean);
@@ -388,6 +395,7 @@ package android.net {
   }
 
   public abstract class SocketKeepalive implements java.lang.AutoCloseable {
+    field public static final int ERROR_NO_SUCH_SLOT = -33; // 0xffffffdf
     field public static final int SUCCESS = 0; // 0x0
   }
 
diff --git a/framework/src/android/net/NetworkAgent.java b/framework/src/android/net/NetworkAgent.java
index 3863ed1113..1ff0140006 100644
--- a/framework/src/android/net/NetworkAgent.java
+++ b/framework/src/android/net/NetworkAgent.java
@@ -362,9 +362,8 @@ public abstract class NetworkAgent {
     public static final int CMD_UNREGISTER_QOS_CALLBACK = BASE + 21;
 
     private static NetworkInfo getLegacyNetworkInfo(final NetworkAgentConfig config) {
-        // The subtype can be changed with (TODO) setLegacySubtype, but it starts
-        // with 0 (TelephonyManager.NETWORK_TYPE_UNKNOWN) and an empty description.
-        final NetworkInfo ni = new NetworkInfo(config.legacyType, 0, config.legacyTypeName, "");
+        final NetworkInfo ni = new NetworkInfo(config.legacyType, config.legacySubType,
+                config.legacyTypeName, config.legacySubTypeName);
         ni.setIsAvailable(true);
         ni.setDetailedState(NetworkInfo.DetailedState.CONNECTING, null /* reason */,
                 config.getLegacyExtraInfo());
@@ -829,6 +828,7 @@ public abstract class NetworkAgent {
      * @hide
      */
     @Deprecated
+    @SystemApi
     public void setLegacySubtype(final int legacySubtype, @NonNull final String legacySubtypeName) {
         mNetworkInfo.setSubtype(legacySubtype, legacySubtypeName);
         queueOrSendNetworkInfo(mNetworkInfo);
@@ -962,6 +962,7 @@ public abstract class NetworkAgent {
      * shall try to overwrite this method and produce a bandwidth update if capable.
      * @hide
      */
+    @SystemApi
     public void onBandwidthUpdateRequested() {
         pollLceData();
     }
diff --git a/framework/src/android/net/NetworkAgentConfig.java b/framework/src/android/net/NetworkAgentConfig.java
index 5e50a6404a..fb6fcc1274 100644
--- a/framework/src/android/net/NetworkAgentConfig.java
+++ b/framework/src/android/net/NetworkAgentConfig.java
@@ -164,6 +164,12 @@ public final class NetworkAgentConfig implements Parcelable {
         return legacyType;
     }
 
+    /**
+     * The legacy Sub type of this network agent, or TYPE_NONE if unset.
+     * @hide
+     */
+    public int legacySubType = ConnectivityManager.TYPE_NONE;
+
     /**
      * Set to true if the PRIVATE_DNS_BROKEN notification has shown for this network.
      * Reset this bit when private DNS mode is changed from strict mode to opportunistic/off mode.
@@ -189,6 +195,13 @@ public final class NetworkAgentConfig implements Parcelable {
         return legacyTypeName;
     }
 
+    /**
+     * The name of the legacy Sub network type. It's a free-form string.
+     * @hide
+     */
+    @NonNull
+    public String legacySubTypeName = "";
+
     /**
      * The legacy extra info of the agent. The extra info should only be :
      * <ul>
@@ -225,6 +238,8 @@ public final class NetworkAgentConfig implements Parcelable {
             skip464xlat = nac.skip464xlat;
             legacyType = nac.legacyType;
             legacyTypeName = nac.legacyTypeName;
+            legacySubType = nac.legacySubType;
+            legacySubTypeName = nac.legacySubTypeName;
             mLegacyExtraInfo = nac.mLegacyExtraInfo;
         }
     }
@@ -290,7 +305,6 @@ public final class NetworkAgentConfig implements Parcelable {
          * and reduce idle traffic on networks that are known to be IPv6-only without a NAT64.
          *
          * @return this builder, to facilitate chaining.
-         * @hide
          */
         @NonNull
         public Builder disableNat64Detection() {
@@ -303,7 +317,6 @@ public final class NetworkAgentConfig implements Parcelable {
          * perform its own carrier-specific provisioning procedure.
          *
          * @return this builder, to facilitate chaining.
-         * @hide
          */
         @NonNull
         public Builder disableProvisioningNotification() {
@@ -323,6 +336,18 @@ public final class NetworkAgentConfig implements Parcelable {
             return this;
         }
 
+        /**
+         * Sets the legacy sub-type for this network.
+         *
+         * @param legacySubType the type
+         * @return this builder, to facilitate chaining.
+         */
+        @NonNull
+        public Builder setLegacySubType(final int legacySubType) {
+            mConfig.legacySubType = legacySubType;
+            return this;
+        }
+
         /**
          * Sets the name of the legacy type of the agent. It's a free-form string used in logging.
          * @param legacyTypeName the name
@@ -334,11 +359,21 @@ public final class NetworkAgentConfig implements Parcelable {
             return this;
         }
 
+        /**
+         * Sets the name of the legacy Sub-type of the agent. It's a free-form string.
+         * @param legacySubTypeName the name
+         * @return this builder, to facilitate chaining.
+         */
+        @NonNull
+        public Builder setLegacySubTypeName(@NonNull String legacySubTypeName) {
+            mConfig.legacySubTypeName = legacySubTypeName;
+            return this;
+        }
+
         /**
          * Sets the legacy extra info of the agent.
          * @param legacyExtraInfo the legacy extra info.
          * @return this builder, to facilitate chaining.
-         * @hide
          */
         @NonNull
         public Builder setLegacyExtraInfo(@NonNull String legacyExtraInfo) {
@@ -412,6 +447,8 @@ public final class NetworkAgentConfig implements Parcelable {
         out.writeInt(skip464xlat ? 1 : 0);
         out.writeInt(legacyType);
         out.writeString(legacyTypeName);
+        out.writeInt(legacySubType);
+        out.writeString(legacySubTypeName);
         out.writeString(mLegacyExtraInfo);
     }
 
@@ -429,6 +466,8 @@ public final class NetworkAgentConfig implements Parcelable {
             networkAgentConfig.skip464xlat = in.readInt() != 0;
             networkAgentConfig.legacyType = in.readInt();
             networkAgentConfig.legacyTypeName = in.readString();
+            networkAgentConfig.legacySubType = in.readInt();
+            networkAgentConfig.legacySubTypeName = in.readString();
             networkAgentConfig.mLegacyExtraInfo = in.readString();
             return networkAgentConfig;
         }
diff --git a/framework/src/android/net/SocketKeepalive.java b/framework/src/android/net/SocketKeepalive.java
index d007a9520c..f6cae72516 100644
--- a/framework/src/android/net/SocketKeepalive.java
+++ b/framework/src/android/net/SocketKeepalive.java
@@ -55,36 +55,68 @@ public abstract class SocketKeepalive implements AutoCloseable {
     static final String TAG = "SocketKeepalive";
 
     /**
-     * No errors.
+     * Success. It indicates there is no error.
      * @hide
      */
     @SystemApi
     public static final int SUCCESS = 0;
 
-    /** @hide */
+    /**
+     * No keepalive. This should only be internally as it indicates There is no keepalive.
+     * It should not propagate to applications.
+     * @hide
+     */
     public static final int NO_KEEPALIVE = -1;
 
-    /** @hide */
+    /**
+     * Data received.
+     * @hide
+     */
     public static final int DATA_RECEIVED = -2;
 
-    /** @hide */
+    /**
+     * The binder died.
+     * @hide
+     */
     public static final int BINDER_DIED = -10;
 
-    /** The specified {@code Network} is not connected. */
+    /**
+     * The invalid network. It indicates the specified {@code Network} is not connected.
+     */
     public static final int ERROR_INVALID_NETWORK = -20;
-    /** The specified IP addresses are invalid. For example, the specified source IP address is
-     * not configured on the specified {@code Network}. */
+
+    /**
+     * The invalid IP addresses. Indicates the specified IP addresses are invalid.
+     * For example, the specified source IP address is not configured on the
+     * specified {@code Network}.
+     */
     public static final int ERROR_INVALID_IP_ADDRESS = -21;
-    /** The requested port is invalid. */
+
+    /**
+     * The port is invalid.
+     */
     public static final int ERROR_INVALID_PORT = -22;
-    /** The packet length is invalid (e.g., too long). */
+
+    /**
+     * The length is invalid (e.g. too long).
+     */
     public static final int ERROR_INVALID_LENGTH = -23;
-    /** The packet transmission interval is invalid (e.g., too short). */
+
+    /**
+     * The interval is invalid (e.g. too short).
+     */
     public static final int ERROR_INVALID_INTERVAL = -24;
-    /** The target socket is invalid. */
+
+    /**
+     * The socket is invalid.
+     */
     public static final int ERROR_INVALID_SOCKET = -25;
-    /** The target socket is not idle. */
+
+    /**
+     * The socket is not idle.
+     */
     public static final int ERROR_SOCKET_NOT_IDLE = -26;
+
     /**
      * The stop reason is uninitialized. This should only be internally used as initial state
      * of stop reason, instead of propagating to application.
@@ -92,15 +124,29 @@ public abstract class SocketKeepalive implements AutoCloseable {
      */
     public static final int ERROR_STOP_REASON_UNINITIALIZED = -27;
 
-    /** The device does not support this request. */
+    /**
+     * The request is unsupported.
+     */
     public static final int ERROR_UNSUPPORTED = -30;
-    /** @hide TODO: delete when telephony code has been updated. */
-    public static final int ERROR_HARDWARE_UNSUPPORTED = ERROR_UNSUPPORTED;
-    /** The hardware returned an error. */
+
+    /**
+     * There was a hardware error.
+     */
     public static final int ERROR_HARDWARE_ERROR = -31;
-    /** The limitation of resource is reached. */
+
+    /**
+     * Resources are insufficient (e.g. all hardware slots are in use).
+     */
     public static final int ERROR_INSUFFICIENT_RESOURCES = -32;
 
+    /**
+     * There was no such slot. This should only be internally as it indicates
+     * a programming error in the system server. It should not propagate to
+     * applications.
+     * @hide
+     */
+    @SystemApi
+    public static final int ERROR_NO_SUCH_SLOT = -33;
 
     /** @hide */
     @Retention(RetentionPolicy.SOURCE)
@@ -111,7 +157,8 @@ public abstract class SocketKeepalive implements AutoCloseable {
             ERROR_INVALID_LENGTH,
             ERROR_INVALID_INTERVAL,
             ERROR_INVALID_SOCKET,
-            ERROR_SOCKET_NOT_IDLE
+            ERROR_SOCKET_NOT_IDLE,
+            ERROR_NO_SUCH_SLOT
     })
     public @interface ErrorCode {}
 
@@ -122,7 +169,6 @@ public abstract class SocketKeepalive implements AutoCloseable {
             ERROR_INVALID_LENGTH,
             ERROR_UNSUPPORTED,
             ERROR_INSUFFICIENT_RESOURCES,
-            ERROR_HARDWARE_UNSUPPORTED
     })
     public @interface KeepaliveEvent {}
 
diff --git a/services/core/java/com/android/server/connectivity/KeepaliveTracker.java b/services/core/java/com/android/server/connectivity/KeepaliveTracker.java
index 74e4ae7f5b..acf39f05a5 100644
--- a/services/core/java/com/android/server/connectivity/KeepaliveTracker.java
+++ b/services/core/java/com/android/server/connectivity/KeepaliveTracker.java
@@ -26,6 +26,7 @@ import static android.net.SocketKeepalive.ERROR_INVALID_INTERVAL;
 import static android.net.SocketKeepalive.ERROR_INVALID_IP_ADDRESS;
 import static android.net.SocketKeepalive.ERROR_INVALID_NETWORK;
 import static android.net.SocketKeepalive.ERROR_INVALID_SOCKET;
+import static android.net.SocketKeepalive.ERROR_NO_SUCH_SLOT;
 import static android.net.SocketKeepalive.ERROR_STOP_REASON_UNINITIALIZED;
 import static android.net.SocketKeepalive.ERROR_UNSUPPORTED;
 import static android.net.SocketKeepalive.MAX_INTERVAL_SEC;
@@ -528,6 +529,8 @@ public class KeepaliveTracker {
             }
         } else if (reason == ERROR_STOP_REASON_UNINITIALIZED) {
             throw new IllegalStateException("Unexpected stop reason: " + reason);
+        } else if (reason == ERROR_NO_SUCH_SLOT) {
+            throw new IllegalStateException("No such slot: " + reason);
         } else {
             notifyErrorCallback(ki.mCallback, reason);
         }
diff --git a/tests/net/common/java/android/net/NetworkAgentConfigTest.kt b/tests/net/common/java/android/net/NetworkAgentConfigTest.kt
index a4d8353d12..fd126ad8c0 100644
--- a/tests/net/common/java/android/net/NetworkAgentConfigTest.kt
+++ b/tests/net/common/java/android/net/NetworkAgentConfigTest.kt
@@ -44,7 +44,7 @@ class NetworkAgentConfigTest {
             setPartialConnectivityAcceptable(false)
             setUnvalidatedConnectivityAcceptable(true)
         }.build()
-        assertParcelSane(config, 10)
+        assertParcelSane(config, 12)
     }
 
     @Test @IgnoreUpTo(Build.VERSION_CODES.Q)