diff --git a/td/telegram/ConfigShared.cpp b/td/telegram/ConfigShared.cpp
index 0924bf557..4423cb16f 100644
--- a/td/telegram/ConfigShared.cpp
+++ b/td/telegram/ConfigShared.cpp
@@ -133,8 +133,8 @@ tl_object_ptr<td_api::OptionValue> ConfigShared::get_option_value_object(Slice v
   return make_tl_object<td_api::optionValueString>(value.str());
 }
 
-void ConfigShared::on_option_updated(Slice name) {
-  callback_->on_option_updated(name.str());
+void ConfigShared::on_option_updated(Slice name) const {
+  callback_->on_option_updated(name.str(), get_option(name));
 }
 
 }  // namespace td
diff --git a/td/telegram/ConfigShared.h b/td/telegram/ConfigShared.h
index fed5fa5f7..b6c7dbce2 100644
--- a/td/telegram/ConfigShared.h
+++ b/td/telegram/ConfigShared.h
@@ -25,7 +25,7 @@ class ConfigShared {
     Callback(const Callback &) = delete;
     Callback &operator=(const Callback &) = delete;
     virtual ~Callback() = default;
-    virtual void on_option_updated(const string &name) = 0;
+    virtual void on_option_updated(const string &name, const string &value) = 0;
   };
 
   ConfigShared(BinlogPmcPtr config_pmc, unique_ptr<Callback> callback);
@@ -53,7 +53,7 @@ class ConfigShared {
   bool set_option(Slice name, Slice value);
   static tl_object_ptr<td_api::OptionValue> get_option_value_object(Slice value);
 
-  void on_option_updated(Slice name);
+  void on_option_updated(Slice name) const;
 };
 
 }  // namespace td
diff --git a/td/telegram/Td.cpp b/td/telegram/Td.cpp
index 2067f20db..9405e22b5 100644
--- a/td/telegram/Td.cpp
+++ b/td/telegram/Td.cpp
@@ -4212,8 +4212,7 @@ void Td::on_config_option_updated(const string &name) {
     return;
   }
   if (name == "auth") {
-    on_authorization_lost();
-    return;
+    return on_authorization_lost();
   } else if (name == "saved_animations_limit") {
     return animations_manager_->on_update_saved_animations_limit(G()->shared_config().get_option_integer(name));
   } else if (name == "recent_stickers_limit") {
@@ -4675,7 +4674,18 @@ Status Td::init(DbKey key) {
   VLOG(td_init) << "Create ConfigManager and ConfigShared";
   class ConfigSharedCallback : public ConfigShared::Callback {
    public:
-    void on_option_updated(const string &name) override {
+    void on_option_updated(const string &name, const string &value) override {
+      if (name == "is_emulator" && !G()->close_flag()) {
+        // it should be applied immediately, because it affects MtprotoHeader
+        if (G()->have_mtproto_header()) {
+          // can't use G()->shared_config(), because it may be not created yet
+          G()->mtproto_header().set_is_emulator(value == "Btrue");
+        }
+        if (G()->have_net_query_dispatcher()) {
+          G()->net_query_dispatcher().update_mtproto_header();
+        }
+      }
+
       send_closure(G()->td(), &Td::on_config_option_updated, name);
     }
   };
@@ -5087,6 +5097,7 @@ Status Td::set_parameters(td_api::object_ptr<td_api::tdlibParameters> parameters
     options.application_version += ", TDLib ";
     options.application_version += TDLIB_VERSION;
   }
+  options.is_emulator = false;
   options.proxy = Proxy();
   G()->set_mtproto_header(std::make_unique<MtprotoHeader>(options));
 
@@ -6624,6 +6635,11 @@ void Td::on_request(uint64 id, td_api::setOption &request) {
         return;
       }
       break;
+    case 'i':
+      if (set_boolean_option("is_emulator")) {
+        return;
+      }
+      break;
     case 'o':
       if (request.name_ == "online") {
         if (value_constructor_id != td_api::optionValueBoolean::ID &&
diff --git a/td/telegram/cli.cpp b/td/telegram/cli.cpp
index 3ef76e95e..b130cc136 100644
--- a/td/telegram/cli.cpp
+++ b/td/telegram/cli.cpp
@@ -665,34 +665,40 @@ class CliClient final : public Actor {
     close_flag_ = false;
     ready_to_stop_ = false;
 
-    td_ = create_actor<ClientActor>("ClientActor1", make_td_callback());
+    bool test_init = false;
+
+    if (test_init) {
+      td_ = create_actor<ClientActor>("ClientActor1", make_td_callback());
+    }
     td_ = create_actor<ClientActor>("ClientActor2", make_td_callback());
     ready_to_stop_ = false;
 
-    for (int i = 0; i < 4; i++) {
-      send_closure_later(td_, &ClientActor::request, std::numeric_limits<uint64>::max(),
-                         td_api::make_object<td_api::setAlarm>(0.001 + 1000 * (i / 2)));
+    if (test_init) {
+      for (int i = 0; i < 4; i++) {
+        send_closure_later(td_, &ClientActor::request, std::numeric_limits<uint64>::max(),
+                           td_api::make_object<td_api::setAlarm>(0.001 + 1000 * (i / 2)));
+      }
+
+      send_request(td_api::make_object<td_api::getTextEntities>(
+          "@telegram /test_command https://telegram.org telegram.me @gif @test"));
+
+      send_request(td_api::make_object<td_api::getOption>("use_pfs"));
+      send_request(td_api::make_object<td_api::setOption>(
+          "use_pfs", td_api::make_object<td_api::optionValueBoolean>(std::time(nullptr) / 86400 % 2 == 0)));
+      send_request(td_api::make_object<td_api::setOption>("use_storage_optimizer",
+                                                          td_api::make_object<td_api::optionValueBoolean>(false)));
+
+      send_request(td_api::make_object<td_api::setNetworkType>(td_api::make_object<td_api::networkTypeWiFi>()));
+      send_request(td_api::make_object<td_api::getNetworkStatistics>());
+      send_request(td_api::make_object<td_api::getCountryCode>());
+
+      auto bad_parameters = td_api::make_object<td_api::tdlibParameters>();
+      bad_parameters->database_directory_ = "/..";
+      bad_parameters->api_id_ = api_id_;
+      bad_parameters->api_hash_ = api_hash_;
+      send_request(td_api::make_object<td_api::setTdlibParameters>(std::move(bad_parameters)));
     }
 
-    send_request(td_api::make_object<td_api::getTextEntities>(
-        "@telegram /test_command https://telegram.org telegram.me @gif @test"));
-
-    send_request(td_api::make_object<td_api::getOption>("use_pfs"));
-    send_request(td_api::make_object<td_api::setOption>(
-        "use_pfs", td_api::make_object<td_api::optionValueBoolean>(std::time(nullptr) / 86400 % 2 == 0)));
-    send_request(td_api::make_object<td_api::setOption>("use_storage_optimizer",
-                                                        td_api::make_object<td_api::optionValueBoolean>(false)));
-
-    send_request(td_api::make_object<td_api::setNetworkType>(td_api::make_object<td_api::networkTypeWiFi>()));
-    send_request(td_api::make_object<td_api::getNetworkStatistics>());
-    send_request(td_api::make_object<td_api::getCountryCode>());
-
-    auto bad_parameters = td_api::make_object<td_api::tdlibParameters>();
-    bad_parameters->database_directory_ = "/..";
-    bad_parameters->api_id_ = api_id_;
-    bad_parameters->api_hash_ = api_hash_;
-    send_request(td_api::make_object<td_api::setTdlibParameters>(std::move(bad_parameters)));
-
     auto parameters = td_api::make_object<td_api::tdlibParameters>();
     parameters->use_test_dc_ = use_test_dc_;
     parameters->use_message_database_ = true;
diff --git a/td/telegram/net/MtprotoHeader.cpp b/td/telegram/net/MtprotoHeader.cpp
index f0e4f5d7a..83d33b447 100644
--- a/td/telegram/net/MtprotoHeader.cpp
+++ b/td/telegram/net/MtprotoHeader.cpp
@@ -28,9 +28,13 @@ class HeaderStorer {
     // system_lang_code:string lang_pack:string lang_code:string proxy:flags.0?InputClientProxy query:!X = X;
     store(static_cast<int32>(0x785188b8), storer);
     int32 flags = 0;
-    if (!is_anonymous && options.proxy.type() == Proxy::Type::Mtproto) {
+    bool have_proxy = !is_anonymous && options.proxy.type() == Proxy::Type::Mtproto;
+    if (have_proxy) {
       flags |= 1 << 0;
     }
+    if (options.is_emulator) {
+      flags |= 1 << 10;
+    }
     store(flags, storer);
     store(options.api_id, storer);
     if (is_anonymous) {
@@ -44,7 +48,7 @@ class HeaderStorer {
     store(options.system_language_code, storer);
     store(string(), storer);
     store(string(), storer);
-    if ((flags & 1) != 0) {
+    if (have_proxy) {
       // inputClientProxy#75588b3f address:string port:int = InputClientProxy;
       store(static_cast<int32>(0x75588b3f), storer);
       store(Slice(options.proxy.server()), storer);
diff --git a/td/telegram/net/MtprotoHeader.h b/td/telegram/net/MtprotoHeader.h
index 5c9ec6032..c3621337a 100644
--- a/td/telegram/net/MtprotoHeader.h
+++ b/td/telegram/net/MtprotoHeader.h
@@ -20,6 +20,7 @@ class MtprotoHeader {
     string system_language_code;
     string device_model;
     string system_version;
+    bool is_emulator = false;
     string application_version;
     Proxy proxy;
   };
@@ -33,6 +34,11 @@ class MtprotoHeader {
     default_header_ = gen_header(options_, false);
   }
 
+  void set_is_emulator(bool is_emulator) {
+    options_.is_emulator = is_emulator;
+    default_header_ = gen_header(options_, false);
+  }
+
   Slice get_default_header() const {
     return default_header_;
   }