diff --git a/Tethering/src/com/android/networkstack/tethering/Tethering.java b/Tethering/src/com/android/networkstack/tethering/Tethering.java
index 552b105..873961a 100644
--- a/Tethering/src/com/android/networkstack/tethering/Tethering.java
+++ b/Tethering/src/com/android/networkstack/tethering/Tethering.java
@@ -368,6 +368,7 @@
 
         // Load tethering configuration.
         updateConfiguration();
+        mConfig.readEnableSyncSM(mContext);
         // It is OK for the configuration to be passed to the PrivateAddressCoordinator at
         // construction time because the only part of the configuration it uses is
         // shouldEnableWifiP2pDedicatedIp(), and currently do not support changing that.
diff --git a/Tethering/src/com/android/networkstack/tethering/TetheringConfiguration.java b/Tethering/src/com/android/networkstack/tethering/TetheringConfiguration.java
index 0678525..298940e 100644
--- a/Tethering/src/com/android/networkstack/tethering/TetheringConfiguration.java
+++ b/Tethering/src/com/android/networkstack/tethering/TetheringConfiguration.java
@@ -132,6 +132,9 @@
 
     public static final String TETHER_FORCE_RANDOM_PREFIX_BASE_SELECTION =
             "tether_force_random_prefix_base_selection";
+
+    public static final String TETHER_ENABLE_SYNC_SM = "tether_enable_sync_sm";
+
     /**
      * Default value that used to periodic polls tether offload stats from tethering offload HAL
      * to make the data warnings work.
@@ -139,7 +142,7 @@
     public static final int DEFAULT_TETHER_OFFLOAD_POLL_INTERVAL_MS = 5000;
 
     /** A flag for using synchronous or asynchronous state machine. */
-    public static final boolean USE_SYNC_SM = false;
+    public static boolean USE_SYNC_SM = false;
 
     public final String[] tetherableUsbRegexs;
     public final String[] tetherableWifiRegexs;
@@ -385,6 +388,16 @@
         return mRandomPrefixBase;
     }
 
+    /**
+     * Check whether sync SM is enabled then set it to USE_SYNC_SM. This should be called once
+     * when tethering is created. Otherwise if the flag is pushed while tethering is enabled,
+     * then it's possible for some IpServer(s) running the new sync state machine while others
+     * use the async state machine.
+     */
+    public void readEnableSyncSM(final Context ctx) {
+        USE_SYNC_SM = mDeps.isFeatureEnabled(ctx, TETHER_ENABLE_SYNC_SM);
+    }
+
     /** Does the dumping.*/
     public void dump(PrintWriter pw) {
         pw.print("activeDataSubId: ");
@@ -438,6 +451,9 @@
 
         pw.print("mRandomPrefixBase: ");
         pw.println(mRandomPrefixBase);
+
+        pw.print("USE_SYNC_SM: ");
+        pw.println(USE_SYNC_SM);
     }
 
     /** Returns the string representation of this object.*/
diff --git a/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringConfigurationTest.java b/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringConfigurationTest.java
index aa322dc..dd51c7a 100644
--- a/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringConfigurationTest.java
+++ b/Tethering/tests/unit/src/com/android/networkstack/tethering/TetheringConfigurationTest.java
@@ -754,4 +754,27 @@
                 new TetheringConfiguration(mMockContext, mLog, INVALID_SUBSCRIPTION_ID, mDeps);
         assertEquals(p2pLeasesSubnetPrefixLength, p2pCfg.getP2pLeasesSubnetPrefixLength());
     }
+
+    private void setTetherEnableSyncSMFlagEnabled(Boolean enabled) {
+        mDeps.setFeatureEnabled(TetheringConfiguration.TETHER_ENABLE_SYNC_SM, enabled);
+        new TetheringConfiguration(
+                mMockContext, mLog, INVALID_SUBSCRIPTION_ID, mDeps).readEnableSyncSM(mMockContext);
+    }
+
+    private void assertEnableSyncSM(boolean value) {
+        assertEquals(value, TetheringConfiguration.USE_SYNC_SM);
+    }
+
+    @Test
+    public void testEnableSyncSMFlag() throws Exception {
+        // Test default disabled
+        setTetherEnableSyncSMFlagEnabled(null);
+        assertEnableSyncSM(false);
+
+        setTetherEnableSyncSMFlagEnabled(true);
+        assertEnableSyncSM(true);
+
+        setTetherEnableSyncSMFlagEnabled(false);
+        assertEnableSyncSM(false);
+    }
 }