diff --git a/telephony/java/android/telephony/CarrierConfigManager.java b/telephony/java/android/telephony/CarrierConfigManager.java
index 111ffe084ef1d..ec7a20c5ca3f9 100644
--- a/telephony/java/android/telephony/CarrierConfigManager.java
+++ b/telephony/java/android/telephony/CarrierConfigManager.java
@@ -4076,6 +4076,18 @@ public class CarrierConfigManager {
     public static final String KEY_USE_LOWER_MTU_VALUE_IF_BOTH_RECEIVED =
             "use_lower_mtu_value_if_both_received";
 
+    /**
+     * Determines the default RTT mode.
+     *
+     * Upon first boot, when the user has not yet set a value for their preferred RTT mode,
+     * the value of this config will be sent to the IMS stack. Valid values are the same as for
+     * {@link Settings.Secure#RTT_CALLING_MODE}.
+     *
+     * @hide
+     */
+    public static final String KEY_DEFAULT_RTT_MODE_INT =
+            "default_rtt_mode_int";
+
     /**
      * Indicates if auto-configuration server is used for the RCS config
      * Reference: GSMA RCC.14
@@ -4636,6 +4648,7 @@ public class CarrierConfigManager {
         sDefaults.putBoolean(KEY_USE_LOWER_MTU_VALUE_IF_BOTH_RECEIVED, false);
         sDefaults.putBoolean(KEY_USE_ACS_FOR_RCS_BOOL, false);
         sDefaults.putBoolean(KEY_NETWORK_TEMP_NOT_METERED_SUPPORTED_BOOL, false);
+        sDefaults.putInt(KEY_DEFAULT_RTT_MODE_INT, 0);
     }
 
     /**