diff --git a/DEPS b/DEPS
index 864cc8b6ab0..a2a66bce119 100644
--- a/DEPS
+++ b/DEPS
@@ -145,7 +145,7 @@ deps = {
    # and not have to specific specific hashes.
 
   'src/third_party/tonic':
-   Var('fuchsia_git') + '/tonic' + '@' + 'bd27b4549199df72fcaeefd259ebc12a31c2e4ee',
+   Var('fuchsia_git') + '/tonic' + '@' + '1a8ed9be2e2b56b32e888266d6db465d36012df4',
 
   'src/third_party/benchmark':
    Var('fuchsia_git') + '/third_party/benchmark' + '@' + 'a779ffce872b4c811beef482e18bd0b63626aa42',
diff --git a/engine/src/flutter/common/settings.h b/engine/src/flutter/common/settings.h
index 2ebcbf0cd86..761b7734fbf 100644
--- a/engine/src/flutter/common/settings.h
+++ b/engine/src/flutter/common/settings.h
@@ -183,6 +183,14 @@ struct Settings {
   // soon as a frame is rasterized.
   FrameRasterizedCallback frame_rasterized_callback;
 
+  // This data will be available to the isolate immediately on launch via the
+  // Window.getPersistentIsolateData callback. This is meant for information
+  // that the isolate cannot request asynchronously (platform messages can be
+  // used for that purpose). This data is held for the lifetime of the shell and
+  // is available on isolate restarts in the the shell instance. Due to this,
+  // the buffer must be as small as possible.
+  std::shared_ptr<const fml::Mapping> persistent_isolate_data;
+
   std::string ToString() const;
 };
 
diff --git a/engine/src/flutter/fml/mapping.cc b/engine/src/flutter/fml/mapping.cc
index c349c5b30e0..d76efa799dc 100644
--- a/engine/src/flutter/fml/mapping.cc
+++ b/engine/src/flutter/fml/mapping.cc
@@ -4,6 +4,7 @@
 
 #include "flutter/fml/mapping.h"
 
+#include <algorithm>
 #include <sstream>
 
 namespace fml {
@@ -67,6 +68,9 @@ std::unique_ptr<FileMapping> FileMapping::CreateReadExecute(
 
 DataMapping::DataMapping(std::vector<uint8_t> data) : data_(std::move(data)) {}
 
+DataMapping::DataMapping(const std::string& string)
+    : data_(string.begin(), string.end()) {}
+
 DataMapping::~DataMapping() = default;
 
 size_t DataMapping::GetSize() const {
diff --git a/engine/src/flutter/fml/mapping.h b/engine/src/flutter/fml/mapping.h
index cd077bd4483..6cdcc2bae55 100644
--- a/engine/src/flutter/fml/mapping.h
+++ b/engine/src/flutter/fml/mapping.h
@@ -86,6 +86,8 @@ class DataMapping final : public Mapping {
  public:
   DataMapping(std::vector<uint8_t> data);
 
+  DataMapping(const std::string& string);
+
   ~DataMapping() override;
 
   // |Mapping|
diff --git a/engine/src/flutter/lib/ui/window.dart b/engine/src/flutter/lib/ui/window.dart
index a810551e382..3bd28a248bb 100644
--- a/engine/src/flutter/lib/ui/window.dart
+++ b/engine/src/flutter/lib/ui/window.dart
@@ -1176,6 +1176,18 @@ class Window {
       registrationZone.runUnaryGuarded(callback, data);
     };
   }
+
+
+  /// The embedder can specify data that the isolate can request synchronously
+  /// on launch. This accessor fetches that data.
+  ///
+  /// This data is persistent for the duration of the Flutter application and is
+  /// available even after isolate restarts. Because of this lifecycle, the size
+  /// of this data must be kept to a minimum.
+  ///
+  /// For asynchronous communication between the embedder and isolate, a
+  /// platform channel may be used.
+  ByteData getPersistentIsolateData() native 'Window_getPersistentIsolateData';
 }
 
 /// Additional accessibility features that may be enabled by the platform.
diff --git a/engine/src/flutter/lib/ui/window/window.cc b/engine/src/flutter/lib/ui/window/window.cc
index 7d3ab8ee5ec..5f5ae1dbe3d 100644
--- a/engine/src/flutter/lib/ui/window/window.cc
+++ b/engine/src/flutter/lib/ui/window/window.cc
@@ -142,6 +142,20 @@ void _RespondToPlatformMessage(Dart_NativeArguments args) {
   tonic::DartCallStatic(&RespondToPlatformMessage, args);
 }
 
+void GetPersistentIsolateData(Dart_NativeArguments args) {
+  auto persistent_isolate_data =
+      UIDartState::Current()->window()->client()->GetPersistentIsolateData();
+
+  if (!persistent_isolate_data) {
+    Dart_SetReturnValue(args, Dart_Null());
+    return;
+  }
+
+  Dart_SetReturnValue(
+      args, tonic::DartByteData::Create(persistent_isolate_data->GetMapping(),
+                                        persistent_isolate_data->GetSize()));
+}
+
 }  // namespace
 
 Dart_Handle ToByteData(const std::vector<uint8_t>& buffer) {
@@ -398,6 +412,7 @@ void Window::RegisterNatives(tonic::DartLibraryNatives* natives) {
       {"Window_setIsolateDebugName", SetIsolateDebugName, 2, true},
       {"Window_reportUnhandledException", ReportUnhandledException, 2, true},
       {"Window_setNeedsReportTimings", SetNeedsReportTimings, 2, true},
+      {"Window_getPersistentIsolateData", GetPersistentIsolateData, 1, true},
   });
 }
 
diff --git a/engine/src/flutter/lib/ui/window/window.h b/engine/src/flutter/lib/ui/window/window.h
index 99a8585a691..bddcb70f315 100644
--- a/engine/src/flutter/lib/ui/window/window.h
+++ b/engine/src/flutter/lib/ui/window/window.h
@@ -57,6 +57,7 @@ class WindowClient {
   virtual void UpdateIsolateDescription(const std::string isolate_name,
                                         int64_t isolate_port) = 0;
   virtual void SetNeedsReportTimings(bool value) = 0;
+  virtual std::shared_ptr<const fml::Mapping> GetPersistentIsolateData() = 0;
 
  protected:
   virtual ~WindowClient();
diff --git a/engine/src/flutter/lib/web_ui/lib/src/ui/window.dart b/engine/src/flutter/lib/web_ui/lib/src/ui/window.dart
index 80f15c712d1..47d27257be5 100644
--- a/engine/src/flutter/lib/web_ui/lib/src/ui/window.dart
+++ b/engine/src/flutter/lib/web_ui/lib/src/ui/window.dart
@@ -995,6 +995,8 @@ abstract class Window {
   String _initialLifecycleState;
 
   void setIsolateDebugName(String name) {}
+
+  ByteData getPersistentIsolateData() => null;
 }
 
 VoidCallback webOnlyScheduleFrameCallback;
diff --git a/engine/src/flutter/runtime/runtime_controller.cc b/engine/src/flutter/runtime/runtime_controller.cc
index 7cc771ff8dd..61415ec4124 100644
--- a/engine/src/flutter/runtime/runtime_controller.cc
+++ b/engine/src/flutter/runtime/runtime_controller.cc
@@ -26,7 +26,8 @@ RuntimeController::RuntimeController(
     std::string p_advisory_script_entrypoint,
     std::function<void(int64_t)> p_idle_notification_callback,
     fml::closure p_isolate_create_callback,
-    fml::closure p_isolate_shutdown_callback)
+    fml::closure p_isolate_shutdown_callback,
+    std::shared_ptr<const fml::Mapping> p_persistent_isolate_data)
     : RuntimeController(p_client,
                         p_vm,
                         std::move(p_isolate_snapshot),
@@ -39,7 +40,8 @@ RuntimeController::RuntimeController(
                         p_idle_notification_callback,
                         WindowData{/* default window data */},
                         p_isolate_create_callback,
-                        p_isolate_shutdown_callback) {}
+                        p_isolate_shutdown_callback,
+                        std::move(p_persistent_isolate_data)) {}
 
 RuntimeController::RuntimeController(
     RuntimeDelegate& p_client,
@@ -54,7 +56,8 @@ RuntimeController::RuntimeController(
     std::function<void(int64_t)> idle_notification_callback,
     WindowData p_window_data,
     fml::closure p_isolate_create_callback,
-    fml::closure p_isolate_shutdown_callback)
+    fml::closure p_isolate_shutdown_callback,
+    std::shared_ptr<const fml::Mapping> p_persistent_isolate_data)
     : client_(p_client),
       vm_(p_vm),
       isolate_snapshot_(std::move(p_isolate_snapshot)),
@@ -67,7 +70,8 @@ RuntimeController::RuntimeController(
       idle_notification_callback_(idle_notification_callback),
       window_data_(std::move(p_window_data)),
       isolate_create_callback_(p_isolate_create_callback),
-      isolate_shutdown_callback_(p_isolate_shutdown_callback) {
+      isolate_shutdown_callback_(p_isolate_shutdown_callback),
+      persistent_isolate_data_(std::move(p_persistent_isolate_data)) {
   // Create the root isolate as soon as the runtime controller is initialized.
   // It will be run at a later point when the engine provides a run
   // configuration and then runs the isolate.
@@ -144,7 +148,8 @@ std::unique_ptr<RuntimeController> RuntimeController::Clone() const {
       idle_notification_callback_,  //
       window_data_,                 //
       isolate_create_callback_,     //
-      isolate_shutdown_callback_    //
+      isolate_shutdown_callback_,   //
+      persistent_isolate_data_      //
       ));
 }
 
@@ -296,42 +301,56 @@ Window* RuntimeController::GetWindowIfAvailable() {
   return root_isolate ? root_isolate->window() : nullptr;
 }
 
+// |WindowClient|
 std::string RuntimeController::DefaultRouteName() {
   return client_.DefaultRouteName();
 }
 
+// |WindowClient|
 void RuntimeController::ScheduleFrame() {
   client_.ScheduleFrame();
 }
 
+// |WindowClient|
 void RuntimeController::Render(Scene* scene) {
   client_.Render(scene->takeLayerTree());
 }
 
+// |WindowClient|
 void RuntimeController::UpdateSemantics(SemanticsUpdate* update) {
   if (window_data_.semantics_enabled) {
     client_.UpdateSemantics(update->takeNodes(), update->takeActions());
   }
 }
 
+// |WindowClient|
 void RuntimeController::HandlePlatformMessage(
     fml::RefPtr<PlatformMessage> message) {
   client_.HandlePlatformMessage(std::move(message));
 }
 
+// |WindowClient|
 FontCollection& RuntimeController::GetFontCollection() {
   return client_.GetFontCollection();
 }
 
+// |WindowClient|
 void RuntimeController::UpdateIsolateDescription(const std::string isolate_name,
                                                  int64_t isolate_port) {
   client_.UpdateIsolateDescription(isolate_name, isolate_port);
 }
 
+// |WindowClient|
 void RuntimeController::SetNeedsReportTimings(bool value) {
   client_.SetNeedsReportTimings(value);
 }
 
+// |WindowClient|
+std::shared_ptr<const fml::Mapping>
+RuntimeController::GetPersistentIsolateData() {
+  return persistent_isolate_data_;
+}
+
 Dart_Port RuntimeController::GetMainPort() {
   std::shared_ptr<DartIsolate> root_isolate = root_isolate_.lock();
   return root_isolate ? root_isolate->main_port() : ILLEGAL_PORT;
diff --git a/engine/src/flutter/runtime/runtime_controller.h b/engine/src/flutter/runtime/runtime_controller.h
index 845bc45ef3b..665f0e17dbb 100644
--- a/engine/src/flutter/runtime/runtime_controller.h
+++ b/engine/src/flutter/runtime/runtime_controller.h
@@ -28,18 +28,20 @@ class Window;
 
 class RuntimeController final : public WindowClient {
  public:
-  RuntimeController(RuntimeDelegate& client,
-                    DartVM* vm,
-                    fml::RefPtr<const DartSnapshot> isolate_snapshot,
-                    fml::RefPtr<const DartSnapshot> shared_snapshot,
-                    TaskRunners task_runners,
-                    fml::WeakPtr<IOManager> io_manager,
-                    fml::WeakPtr<ImageDecoder> iamge_decoder,
-                    std::string advisory_script_uri,
-                    std::string advisory_script_entrypoint,
-                    std::function<void(int64_t)> idle_notification_callback,
-                    fml::closure isolate_create_callback,
-                    fml::closure isolate_shutdown_callback);
+  RuntimeController(
+      RuntimeDelegate& client,
+      DartVM* vm,
+      fml::RefPtr<const DartSnapshot> isolate_snapshot,
+      fml::RefPtr<const DartSnapshot> shared_snapshot,
+      TaskRunners task_runners,
+      fml::WeakPtr<IOManager> io_manager,
+      fml::WeakPtr<ImageDecoder> iamge_decoder,
+      std::string advisory_script_uri,
+      std::string advisory_script_entrypoint,
+      std::function<void(int64_t)> idle_notification_callback,
+      fml::closure isolate_create_callback,
+      fml::closure isolate_shutdown_callback,
+      std::shared_ptr<const fml::Mapping> persistent_isolate_data);
 
   ~RuntimeController() override;
 
@@ -138,20 +140,23 @@ class RuntimeController final : public WindowClient {
   std::pair<bool, uint32_t> root_isolate_return_code_ = {false, 0};
   const fml::closure isolate_create_callback_;
   const fml::closure isolate_shutdown_callback_;
+  std::shared_ptr<const fml::Mapping> persistent_isolate_data_;
 
-  RuntimeController(RuntimeDelegate& client,
-                    DartVM* vm,
-                    fml::RefPtr<const DartSnapshot> isolate_snapshot,
-                    fml::RefPtr<const DartSnapshot> shared_snapshot,
-                    TaskRunners task_runners,
-                    fml::WeakPtr<IOManager> io_manager,
-                    fml::WeakPtr<ImageDecoder> image_decoder,
-                    std::string advisory_script_uri,
-                    std::string advisory_script_entrypoint,
-                    std::function<void(int64_t)> idle_notification_callback,
-                    WindowData data,
-                    fml::closure isolate_create_callback,
-                    fml::closure isolate_shutdown_callback);
+  RuntimeController(
+      RuntimeDelegate& client,
+      DartVM* vm,
+      fml::RefPtr<const DartSnapshot> isolate_snapshot,
+      fml::RefPtr<const DartSnapshot> shared_snapshot,
+      TaskRunners task_runners,
+      fml::WeakPtr<IOManager> io_manager,
+      fml::WeakPtr<ImageDecoder> image_decoder,
+      std::string advisory_script_uri,
+      std::string advisory_script_entrypoint,
+      std::function<void(int64_t)> idle_notification_callback,
+      WindowData data,
+      fml::closure isolate_create_callback,
+      fml::closure isolate_shutdown_callback,
+      std::shared_ptr<const fml::Mapping> persistent_isolate_data);
 
   Window* GetWindowIfAvailable();
 
@@ -182,6 +187,9 @@ class RuntimeController final : public WindowClient {
   // |WindowClient|
   void SetNeedsReportTimings(bool value) override;
 
+  // |WindowClient|
+  std::shared_ptr<const fml::Mapping> GetPersistentIsolateData() override;
+
   FML_DISALLOW_COPY_AND_ASSIGN(RuntimeController);
 };
 
diff --git a/engine/src/flutter/shell/common/engine.cc b/engine/src/flutter/shell/common/engine.cc
index f106c662daf..b3c889d6b1b 100644
--- a/engine/src/flutter/shell/common/engine.cc
+++ b/engine/src/flutter/shell/common/engine.cc
@@ -69,7 +69,8 @@ Engine::Engine(Delegate& delegate,
       settings_.advisory_script_entrypoint,  // advisory script entrypoint
       settings_.idle_notification_callback,  // idle notification callback
       settings_.isolate_create_callback,     // isolate create callback
-      settings_.isolate_shutdown_callback    // isolate shutdown callback
+      settings_.isolate_shutdown_callback,   // isolate shutdown callback
+      settings_.persistent_isolate_data      // persistent isolate data
   );
 
   pointer_data_dispatcher_ = dispatcher_maker(*this);
diff --git a/engine/src/flutter/shell/common/fixtures/shell_test.dart b/engine/src/flutter/shell/common/fixtures/shell_test.dart
index 05f4782fc64..3c27d561e2c 100644
--- a/engine/src/flutter/shell/common/fixtures/shell_test.dart
+++ b/engine/src/flutter/shell/common/fixtures/shell_test.dart
@@ -110,3 +110,10 @@ void canCreateImageFromDecompressedData() {
     notifyWidthHeight(image.width, image.height);
   });
 }
+
+@pragma('vm:entry-point')
+void canAccessIsolateLaunchData() {
+  notifyMessage(utf8.decode(window.getPersistentIsolateData().buffer.asUint8List()));
+}
+
+void notifyMessage(String string) native 'NotifyMessage';
diff --git a/engine/src/flutter/shell/common/shell_unittests.cc b/engine/src/flutter/shell/common/shell_unittests.cc
index 1871f4ea081..bf9cbc4aea2 100644
--- a/engine/src/flutter/shell/common/shell_unittests.cc
+++ b/engine/src/flutter/shell/common/shell_unittests.cc
@@ -4,6 +4,7 @@
 
 #define FML_USED_ON_EMBEDDER
 
+#include <algorithm>
 #include <functional>
 #include <future>
 #include <memory>
@@ -873,5 +874,43 @@ TEST_F(ShellTest, TextureFrameMarkedAvailableAndUnregister) {
   EXPECT_EQ(mockTexture->unregistered(), true);
 }
 
+TEST_F(ShellTest, IsolateCanAccessPersistentIsolateData) {
+  const std::string message = "dummy isolate launch data.";
+
+  Settings settings = CreateSettingsForFixture();
+  settings.persistent_isolate_data =
+      std::make_shared<fml::DataMapping>(message);
+  TaskRunners task_runners("test",                  // label
+                           GetCurrentTaskRunner(),  // platform
+                           CreateNewThread(),       // gpu
+                           CreateNewThread(),       // ui
+                           CreateNewThread()        // io
+  );
+
+  fml::AutoResetWaitableEvent message_latch;
+  AddNativeCallback("NotifyMessage",
+                    CREATE_NATIVE_ENTRY([&](Dart_NativeArguments args) {
+                      const auto message_from_dart =
+                          tonic::DartConverter<std::string>::FromDart(
+                              Dart_GetNativeArgument(args, 0));
+                      ASSERT_EQ(message, message_from_dart);
+                      message_latch.Signal();
+                    }));
+
+  std::unique_ptr<Shell> shell =
+      CreateShell(std::move(settings), std::move(task_runners));
+
+  ASSERT_TRUE(shell->IsSetup());
+  auto configuration = RunConfiguration::InferFromSettings(settings);
+  configuration.SetEntrypoint("canAccessIsolateLaunchData");
+
+  fml::AutoResetWaitableEvent event;
+  shell->RunEngine(std::move(configuration), [&](auto result) {
+    ASSERT_EQ(result, Engine::RunStatus::Success);
+  });
+
+  message_latch.Wait();
+}
+
 }  // namespace testing
 }  // namespace flutter
diff --git a/engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject.mm b/engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject.mm
index 53bb1b29e89..84fb859cbc4 100644
--- a/engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject.mm
+++ b/engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject.mm
@@ -7,6 +7,7 @@
 #include "flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h"
 
 #include "flutter/common/task_runners.h"
+#include "flutter/fml/mapping.h"
 #include "flutter/fml/message_loop.h"
 #include "flutter/fml/platform/darwin/scoped_nsobject.h"
 #include "flutter/runtime/dart_vm.h"
@@ -234,4 +235,22 @@ static flutter::Settings DefaultSettingsForProcess(NSBundle* bundle = nil) {
   return @"io.flutter.flutter.app";
 }
 
+#pragma mark - Settings utilities
+
+- (void)setPersistentIsolateData:(NSData*)data {
+  if (data == nil) {
+    return;
+  }
+
+  NSData* persistent_isolate_data = [data copy];
+  fml::NonOwnedMapping::ReleaseProc data_release_proc = [persistent_isolate_data](auto, auto) {
+    [persistent_isolate_data release];
+  };
+  _settings.persistent_isolate_data = std::make_shared<fml::NonOwnedMapping>(
+      static_cast<const uint8_t*>(persistent_isolate_data.bytes),  // bytes
+      persistent_isolate_data.length,                              // byte length
+      data_release_proc                                            // release proc
+  );
+}
+
 @end
diff --git a/engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h b/engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h
index 22cee03e9c1..a93af57eaaa 100644
--- a/engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h
+++ b/engine/src/flutter/shell/platform/darwin/ios/framework/Source/FlutterDartProject_Internal.h
@@ -22,6 +22,19 @@ NS_ASSUME_NONNULL_BEGIN
 
 + (NSString*)flutterAssetsName:(NSBundle*)bundle;
 
+/**
+ * The embedder can specify data that the isolate can request synchronously on launch. Engines
+ * launched using this configuration can access the persistent isolate data via the
+ * `Window.getPersistentIsolateData` accessor.
+ *
+ * @param data The persistent isolate data. This data is persistent for the duration of the Flutter
+ *             application and is available even after isolate restarts. Because of this lifecycle,
+ *             the size of this data must be kept to a minimum and platform channels used for
+ *             communication that does not require synchronous embedder to isolate communication
+ *             close to isolate launch.
+ **/
+- (void)setPersistentIsolateData:(NSData*)data;
+
 @end
 
 NS_ASSUME_NONNULL_END