diff --git a/docs/root/api/starting_envoy.rst b/docs/root/api/starting_envoy.rst
index 841d4442db..b11141f34d 100644
--- a/docs/root/api/starting_envoy.rst
+++ b/docs/root/api/starting_envoy.rst
@@ -313,13 +313,16 @@ completes. This interface provides the ability to observe when Envoy has complet
 ready to start dispatching requests. Any requests sent through Envoy before this setup completes
 will be queued automatically, and this function is typically used purely for observability.
 
+The closure passes an opaque handle to the engine so that it can be passed to Envoy's C++ APIs if
+desired.
+
 **Example**::
 
   // Kotlin
-  builder.setOnEngineRunning { /*do something*/ }
+  builder.setOnEngineRunning { engineHandle -> /* do something */ }
 
   // Swift
-  builder.setOnEngineRunning { /*do something*/ }
+  builder.setOnEngineRunning { engineHandle in /* do something */ }
 
 ~~~~~~~~~~~~~
 ``setLogger``
diff --git a/docs/root/intro/version_history.rst b/docs/root/intro/version_history.rst
index 1385bfc3fa..afad524137 100644
--- a/docs/root/intro/version_history.rst
+++ b/docs/root/intro/version_history.rst
@@ -14,6 +14,7 @@ Breaking changes:
 - iOS: enable usage of ``NWPathMonitor`` by default (:issue:`#2329 <2329>`)
 - iOS: replace ``enableNetworkPathMonitor`` with a new ``setNetworkMonitoringMode`` API to allow disabling monitoring (:issue:`#2345 <2345>`)
 - iOS: release artifacts no longer embed bitcode
+- api: the ``setOnEngineRunning`` closure now passes the engine's opaque ID so it can be passed to Envoy's C++ APis
 
 Bugfixes:
 
diff --git a/examples/java/hello_world/MainActivity.java b/examples/java/hello_world/MainActivity.java
index 5d1ebcd4ac..5b0bbc6579 100644
--- a/examples/java/hello_world/MainActivity.java
+++ b/examples/java/hello_world/MainActivity.java
@@ -60,7 +60,7 @@ protected void onCreate(Bundle savedInstanceState) {
 
     engine = new AndroidEngineBuilder(getApplication())
                  .addLogLevel(LogLevel.DEBUG)
-                 .setOnEngineRunning(() -> {
+                 .setOnEngineRunning((ignored) -> {
                    Log.d("MainActivity", "Envoy async internal setup completed");
                    return null;
                  })
diff --git a/examples/objective-c/hello_world/ViewController.m b/examples/objective-c/hello_world/ViewController.m
index 3a989e42cf..8fb1964853 100644
--- a/examples/objective-c/hello_world/ViewController.m
+++ b/examples/objective-c/hello_world/ViewController.m
@@ -39,7 +39,7 @@ - (void)startEnvoy {
   NSLog(@"starting Envoy...");
   EngineBuilder *builder = [[EngineBuilder alloc] init];
   [builder addLogLevel:LogLevelDebug];
-  [builder setOnEngineRunningWithClosure:^{
+  [builder setOnEngineRunningWithClosure:^(NSInteger) {
     NSLog(@"Envoy async internal setup completed");
   }];
 
diff --git a/examples/swift/hello_world/ViewController.swift b/examples/swift/hello_world/ViewController.swift
index 8676c01002..2618478054 100644
--- a/examples/swift/hello_world/ViewController.swift
+++ b/examples/swift/hello_world/ViewController.swift
@@ -24,7 +24,7 @@ final class ViewController: UITableViewController {
       .addPlatformFilter(AsyncDemoFilter.init)
       // swiftlint:disable:next line_length
       .addNativeFilter(name: "envoy.filters.http.buffer", typedConfig: "{\"@type\":\"type.googleapis.com/envoy.extensions.filters.http.buffer.v3.Buffer\",\"max_request_bytes\":5242880}")
-      .setOnEngineRunning { NSLog("Envoy async internal setup completed") }
+      .setOnEngineRunning { _ in NSLog("Envoy async internal setup completed") }
       .addStringAccessor(name: "demo-accessor", accessor: { return "PlatformString" })
       .setEventTracker { NSLog("Envoy event emitted: \($0)") }
       .build()
diff --git a/library/cc/engine_builder.cc b/library/cc/engine_builder.cc
index 5d9477f645..3903fa2411 100644
--- a/library/cc/engine_builder.cc
+++ b/library/cc/engine_builder.cc
@@ -18,7 +18,7 @@ EngineBuilder& EngineBuilder::addLogLevel(LogLevel log_level) {
   return *this;
 }
 
-EngineBuilder& EngineBuilder::setOnEngineRunning(std::function<void()> closure) {
+EngineBuilder& EngineBuilder::setOnEngineRunning(std::function<void(envoy_engine_t)> closure) {
   this->callbacks_->on_engine_running = closure;
   return *this;
 }
diff --git a/library/cc/engine_builder.h b/library/cc/engine_builder.h
index f978fff14c..b6341a7862 100644
--- a/library/cc/engine_builder.h
+++ b/library/cc/engine_builder.h
@@ -16,7 +16,7 @@ class EngineBuilder {
   EngineBuilder();
 
   EngineBuilder& addLogLevel(LogLevel log_level);
-  EngineBuilder& setOnEngineRunning(std::function<void()> closure);
+  EngineBuilder& setOnEngineRunning(std::function<void(envoy_engine_t)> closure);
 
   EngineBuilder& addGrpcStatsDomain(const std::string& stats_domain);
   EngineBuilder& addConnectTimeoutSeconds(int connect_timeout_seconds);
diff --git a/library/cc/engine_callbacks.cc b/library/cc/engine_callbacks.cc
index d76bfa616b..19c50d5898 100644
--- a/library/cc/engine_callbacks.cc
+++ b/library/cc/engine_callbacks.cc
@@ -5,9 +5,9 @@ namespace Platform {
 
 namespace {
 
-void c_on_engine_running(void* context) {
+void c_on_engine_running(envoy_engine_t engine, void* context) {
   auto engine_callbacks = *static_cast<EngineCallbacksSharedPtr*>(context);
-  engine_callbacks->on_engine_running();
+  engine_callbacks->on_engine_running(engine);
 }
 
 void c_on_exit(void* context) {
diff --git a/library/cc/engine_callbacks.h b/library/cc/engine_callbacks.h
index 61c1d196f4..05ccff47ce 100644
--- a/library/cc/engine_callbacks.h
+++ b/library/cc/engine_callbacks.h
@@ -10,7 +10,7 @@ namespace Envoy {
 namespace Platform {
 
 struct EngineCallbacks : public std::enable_shared_from_this<EngineCallbacks> {
-  std::function<void()> on_engine_running;
+  std::function<void(envoy_engine_t)> on_engine_running;
   // unused:
   // std::function<void()> on_exit;
 
diff --git a/library/common/engine.cc b/library/common/engine.cc
index 74b9e34743..59ef1d9f22 100644
--- a/library/common/engine.cc
+++ b/library/common/engine.cc
@@ -122,7 +122,9 @@ envoy_status_t Engine::main(const std::string config, const std::string log_leve
                                                         server_->api().randomGenerator());
           dispatcher_->drain(server_->dispatcher());
           if (callbacks_.on_engine_running != nullptr) {
-            callbacks_.on_engine_running(callbacks_.context);
+            // TODO(jpsim): Update when singleton is removed
+            // reinterpret_cast<envoy_engine_t>(this)
+            callbacks_.on_engine_running(1, callbacks_.context);
           }
         });
   } // mutex_
diff --git a/library/common/jni/jni_interface.cc b/library/common/jni/jni_interface.cc
index 50617b90d4..bee516a742 100644
--- a/library/common/jni/jni_interface.cc
+++ b/library/common/jni/jni_interface.cc
@@ -26,7 +26,7 @@ JNIEXPORT jint JNICALL JNI_OnLoad(JavaVM* vm, void* reserved) {
 
 // JniLibrary
 
-static void jvm_on_engine_running(void* context) {
+static void jvm_on_engine_running(envoy_engine_t engine_handle, void* context) {
   if (context == nullptr) {
     return;
   }
@@ -36,8 +36,8 @@ static void jvm_on_engine_running(void* context) {
   jobject j_context = static_cast<jobject>(context);
   jclass jcls_JvmonEngineRunningContext = env->GetObjectClass(j_context);
   jmethodID jmid_onEngineRunning = env->GetMethodID(
-      jcls_JvmonEngineRunningContext, "invokeOnEngineRunning", "()Ljava/lang/Object;");
-  env->CallObjectMethod(j_context, jmid_onEngineRunning);
+      jcls_JvmonEngineRunningContext, "invokeOnEngineRunning", "(J)Ljava/lang/Object;");
+  env->CallObjectMethod(j_context, jmid_onEngineRunning, static_cast<jlong>(engine_handle));
 
   env->DeleteLocalRef(jcls_JvmonEngineRunningContext);
   // TODO(goaway): This isn't re-used by other engine callbacks, so it's safe to delete here.
diff --git a/library/common/types/c_types.h b/library/common/types/c_types.h
index 92d45b12df..31a940a11c 100644
--- a/library/common/types/c_types.h
+++ b/library/common/types/c_types.h
@@ -406,7 +406,7 @@ typedef void (*envoy_on_exit_f)(void* context);
  * @param context, contains the necessary state to carry out platform-specific dispatch and
  * execution.
  */
-typedef void (*envoy_on_engine_running_f)(void* context);
+typedef void (*envoy_on_engine_running_f)(envoy_engine_t engine, void* context);
 
 /**
  * Called when envoy's logger logs data.
diff --git a/library/java/io/envoyproxy/envoymobile/engine/types/EnvoyOnEngineRunning.java b/library/java/io/envoyproxy/envoymobile/engine/types/EnvoyOnEngineRunning.java
index adb7e3d885..645acb71cf 100644
--- a/library/java/io/envoyproxy/envoymobile/engine/types/EnvoyOnEngineRunning.java
+++ b/library/java/io/envoyproxy/envoymobile/engine/types/EnvoyOnEngineRunning.java
@@ -2,5 +2,5 @@
 
 /* Interface used to support lambdas being passed from Kotlin for engine setup completion. */
 public interface EnvoyOnEngineRunning {
-  Object invokeOnEngineRunning();
+  Object invokeOnEngineRunning(long engineHandle);
 }
diff --git a/library/java/org/chromium/net/impl/CronetUrlRequestContext.java b/library/java/org/chromium/net/impl/CronetUrlRequestContext.java
index c189541b0e..2aa89f1be6 100644
--- a/library/java/org/chromium/net/impl/CronetUrlRequestContext.java
+++ b/library/java/org/chromium/net/impl/CronetUrlRequestContext.java
@@ -83,7 +83,7 @@ public CronetUrlRequestContext(NativeCronetEngineBuilderImpl builder) {
         builder.threadPriority(THREAD_PRIORITY_BACKGROUND + THREAD_PRIORITY_MORE_FAVORABLE);
     mUserAgent = builder.getUserAgent();
     synchronized (mLock) {
-      mEngine = builder.createEngine(() -> {
+      mEngine = builder.createEngine((ignored) -> {
         mNetworkThread = Thread.currentThread();
         android.os.Process.setThreadPriority(threadPriority);
         mInitCompleted.open();
diff --git a/library/kotlin/io/envoyproxy/envoymobile/EngineBuilder.kt b/library/kotlin/io/envoyproxy/envoymobile/EngineBuilder.kt
index 2a29f7be0b..13cf74c976 100644
--- a/library/kotlin/io/envoyproxy/envoymobile/EngineBuilder.kt
+++ b/library/kotlin/io/envoyproxy/envoymobile/EngineBuilder.kt
@@ -21,7 +21,7 @@ class Custom(val yaml: String) : BaseConfiguration()
 open class EngineBuilder(
   private val configuration: BaseConfiguration = Standard()
 ) {
-  protected var onEngineRunning: (() -> Unit) = {}
+  protected var onEngineRunning: ((Long) -> Unit) = {}
   protected var logger: ((String) -> Unit)? = null
   protected var eventTracker: ((Map<String, String>) -> Unit)? = null
   private var engineType: () -> EnvoyEngine = {
@@ -435,7 +435,7 @@ open class EngineBuilder(
    *
    * @return this builder.
    */
-  fun setOnEngineRunning(closure: () -> Unit): EngineBuilder {
+  fun setOnEngineRunning(closure: (Long) -> Unit): EngineBuilder {
     this.onEngineRunning = closure
     return this
   }
diff --git a/library/objective-c/EnvoyEngine.h b/library/objective-c/EnvoyEngine.h
index 0129cece17..646ebab701 100644
--- a/library/objective-c/EnvoyEngine.h
+++ b/library/objective-c/EnvoyEngine.h
@@ -462,7 +462,7 @@ extern const int kEnvoyFailure;
  @param eventTracker Event tracking interface.
  @param networkMonitoringMode Configure how the engines observe network reachability.
  */
-- (instancetype)initWithRunningCallback:(nullable void (^)())onEngineRunning
+- (instancetype)initWithRunningCallback:(nullable void (^)(NSInteger))onEngineRunning
                                  logger:(nullable void (^)(NSString *))logger
                            eventTracker:(nullable void (^)(EnvoyEvent *))eventTracker
                   networkMonitoringMode:(int)networkMonitoringMode;
@@ -586,7 +586,7 @@ extern const int kEnvoyFailure;
 // Concrete implementation of the `EnvoyEngine` interface.
 @interface EnvoyEngineImpl : NSObject <EnvoyEngine>
 
-@property (nonatomic, copy, nullable) void (^onEngineRunning)();
+@property (nonatomic, copy, nullable) void (^onEngineRunning)(NSInteger);
 
 @end
 
diff --git a/library/objective-c/EnvoyEngineImpl.m b/library/objective-c/EnvoyEngineImpl.m
index 3b583fb2a7..708fb4dfcf 100644
--- a/library/objective-c/EnvoyEngineImpl.m
+++ b/library/objective-c/EnvoyEngineImpl.m
@@ -12,13 +12,13 @@
 #import <UIKit/UIKit.h>
 #endif
 
-static void ios_on_engine_running(void *context) {
+static void ios_on_engine_running(envoy_engine_t engine, void *context) {
   // This code block runs inside the Envoy event loop. Therefore, an explicit autoreleasepool block
   // is necessary to act as a breaker for any Objective-C allocation that happens.
   @autoreleasepool {
     EnvoyEngineImpl *engineImpl = (__bridge EnvoyEngineImpl *)context;
     if (engineImpl.onEngineRunning) {
-      engineImpl.onEngineRunning();
+      engineImpl.onEngineRunning(engine);
     }
   }
 }
@@ -435,7 +435,7 @@ @implementation EnvoyEngineImpl {
   EnvoyNetworkMonitor *_networkMonitor;
 }
 
-- (instancetype)initWithRunningCallback:(nullable void (^)())onEngineRunning
+- (instancetype)initWithRunningCallback:(nullable void (^)(NSInteger))onEngineRunning
                                  logger:(nullable void (^)(NSString *))logger
                            eventTracker:(nullable void (^)(EnvoyEvent *))eventTracker
                   networkMonitoringMode:(int)networkMonitoringMode {
diff --git a/library/python/engine_builder_shim.cc b/library/python/engine_builder_shim.cc
index 2966e59d7f..fe768205b2 100644
--- a/library/python/engine_builder_shim.cc
+++ b/library/python/engine_builder_shim.cc
@@ -8,7 +8,8 @@ namespace EngineBuilder {
 
 Platform::EngineBuilder& setOnEngineRunningShim(Platform::EngineBuilder& self,
                                                 std::function<void()> closure) {
-  return self.setOnEngineRunning([closure]() {
+  // TODO(jpsim): Expose engine handle in the Python API
+  return self.setOnEngineRunning([closure](envoy_engine_t) {
     py::gil_scoped_acquire acquire;
     closure();
   });
diff --git a/library/swift/EngineBuilder.swift b/library/swift/EngineBuilder.swift
index 7d5615ebbe..5e76542073 100644
--- a/library/swift/EngineBuilder.swift
+++ b/library/swift/EngineBuilder.swift
@@ -39,7 +39,7 @@ open class EngineBuilder: NSObject {
   private var appVersion: String = "unspecified"
   private var appId: String = "unspecified"
   private var virtualClusters: String = "[]"
-  private var onEngineRunning: (() -> Void)?
+  private var onEngineRunning: ((Int) -> Void)?
   private var logger: ((String) -> Void)?
   private var eventTracker: (([String: String]) -> Void)?
   private(set) var monitoringMode: NetworkMonitoringMode = .pathMonitor
@@ -394,11 +394,12 @@ open class EngineBuilder: NSObject {
 
   /// Set a closure to be called when the engine finishes its async startup and begins running.
   ///
-  /// - parameter closure: The closure to be called.
+  /// - parameter closure: The closure to be called. Passes an engine handle that can be used
+  ///                      to interoperate with Envoy's C++ APIs.
   ///
   /// - returns: This builder.
   @discardableResult
-  public func setOnEngineRunning(closure: @escaping () -> Void) -> Self {
+  public func setOnEngineRunning(closure: @escaping (Int) -> Void) -> Self {
     self.onEngineRunning = closure
     return self
   }
diff --git a/library/swift/mocks/MockEnvoyEngine.swift b/library/swift/mocks/MockEnvoyEngine.swift
index 1f910e9ced..bb360ae6c1 100644
--- a/library/swift/mocks/MockEnvoyEngine.swift
+++ b/library/swift/mocks/MockEnvoyEngine.swift
@@ -3,7 +3,7 @@ import Foundation
 
 /// Mock implementation of `EnvoyEngine`. Used internally for testing the bridging layer & mocking.
 final class MockEnvoyEngine: NSObject {
-  init(runningCallback onEngineRunning: (() -> Void)? = nil, logger: ((String) -> Void)? = nil,
+  init(runningCallback onEngineRunning: ((Int) -> Void)? = nil, logger: ((String) -> Void)? = nil,
        eventTracker: (([String: String]) -> Void)? = nil, networkMonitoringMode: Int32 = 0) {}
 
   /// Closure called when `run(withConfig:)` is called.
diff --git a/test/cc/integration/lifetimes_test.cc b/test/cc/integration/lifetimes_test.cc
index a91aaf069a..64f097228a 100644
--- a/test/cc/integration/lifetimes_test.cc
+++ b/test/cc/integration/lifetimes_test.cc
@@ -82,7 +82,7 @@ void sendRequestEndToEnd() {
   absl::Notification engine_running;
   auto engine_builder = Platform::EngineBuilder(CONFIG_TEMPLATE);
   engine = engine_builder.addLogLevel(Platform::LogLevel::debug)
-               .setOnEngineRunning([&]() { engine_running.Notify(); })
+               .setOnEngineRunning([&](envoy_engine_t) { engine_running.Notify(); })
                .build();
   engine_running.WaitForNotification();
 
diff --git a/test/cc/integration/send_headers_test.cc b/test/cc/integration/send_headers_test.cc
index 0d7482654d..b2d3a3e6db 100644
--- a/test/cc/integration/send_headers_test.cc
+++ b/test/cc/integration/send_headers_test.cc
@@ -60,7 +60,7 @@ TEST(TestSendHeaders, CanSendHeaders) {
   absl::Notification engine_running;
   auto engine_builder = Platform::EngineBuilder(CONFIG_TEMPLATE);
   engine = engine_builder.addLogLevel(Platform::LogLevel::debug)
-               .setOnEngineRunning([&]() { engine_running.Notify(); })
+               .setOnEngineRunning([&](envoy_engine_t) { engine_running.Notify(); })
                .build();
   engine_running.WaitForNotification();
 
diff --git a/test/common/engine_test.cc b/test/common/engine_test.cc
index 30465e6666..131fa8aec4 100644
--- a/test/common/engine_test.cc
+++ b/test/common/engine_test.cc
@@ -70,7 +70,7 @@ TEST_F(EngineTest, EarlyExit) {
   const std::string level = "debug";
 
   engine_test_context test_context{};
-  envoy_engine_callbacks callbacks{[](void* context) -> void {
+  envoy_engine_callbacks callbacks{[](envoy_engine_t, void* context) -> void {
                                      auto* engine_running =
                                          static_cast<engine_test_context*>(context);
                                      engine_running->on_engine_running.Notify();
@@ -97,7 +97,7 @@ TEST_F(EngineTest, AccessEngineAfterInitialization) {
   const std::string level = "debug";
 
   engine_test_context test_context{};
-  envoy_engine_callbacks callbacks{[](void* context) -> void {
+  envoy_engine_callbacks callbacks{[](envoy_engine_t, void* context) -> void {
                                      auto* engine_running =
                                          static_cast<engine_test_context*>(context);
                                      engine_running->on_engine_running.Notify();
diff --git a/test/common/main_interface_test.cc b/test/common/main_interface_test.cc
index c9c22c615d..88bfcddc2b 100644
--- a/test/common/main_interface_test.cc
+++ b/test/common/main_interface_test.cc
@@ -126,7 +126,7 @@ Http::ResponseHeaderMapPtr toResponseHeaders(envoy_headers headers) {
 TEST(MainInterfaceTest, BasicStream) {
   const std::string level = "debug";
   engine_test_context engine_cbs_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
@@ -189,7 +189,7 @@ TEST(MainInterfaceTest, BasicStream) {
 
 TEST(MainInterfaceTest, SendMetadata) {
   engine_test_context engine_cbs_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
@@ -229,7 +229,7 @@ TEST(MainInterfaceTest, SendMetadata) {
 
 TEST(MainInterfaceTest, ResetStream) {
   engine_test_context engine_cbs_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
@@ -301,7 +301,7 @@ TEST(MainInterfaceTest, UsingMainInterfaceWithoutARunningEngine) {
 
 TEST(MainInterfaceTest, RegisterPlatformApi) {
   engine_test_context engine_cbs_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
@@ -331,7 +331,7 @@ TEST(MainInterfaceTest, InitEngineReturns1) {
   // TODO(goaway): return new handle once multiple engine support is in place.
   // https://github.com/envoyproxy/envoy-mobile/issues/332
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
@@ -354,7 +354,7 @@ TEST(MainInterfaceTest, PreferredNetwork) {
 
 TEST(EngineTest, RecordCounter) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
@@ -376,7 +376,7 @@ TEST(EngineTest, RecordCounter) {
 
 TEST(EngineTest, SetGauge) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
@@ -400,7 +400,7 @@ TEST(EngineTest, SetGauge) {
 
 TEST(EngineTest, AddToGauge) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
@@ -424,7 +424,7 @@ TEST(EngineTest, AddToGauge) {
 
 TEST(EngineTest, SubFromGauge) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
@@ -450,7 +450,7 @@ TEST(EngineTest, SubFromGauge) {
 
 TEST(EngineTest, RecordHistogramValue) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
@@ -478,7 +478,7 @@ TEST(EngineTest, RecordHistogramValue) {
 
 TEST(EngineTest, Logger) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* test_context =
                                           static_cast<engine_test_context*>(context);
                                       test_context->on_engine_running.Notify();
@@ -518,7 +518,7 @@ TEST(EngineTest, Logger) {
 
 TEST(EngineTest, EventTrackerRegistersDefaultAPI) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* test_context =
                                           static_cast<engine_test_context*>(context);
                                       test_context->on_engine_running.Notify();
@@ -553,7 +553,7 @@ TEST(EngineTest, EventTrackerRegistersDefaultAPI) {
 
 TEST(EngineTest, EventTrackerRegistersAPI) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* test_context =
                                           static_cast<engine_test_context*>(context);
                                       test_context->on_engine_running.Notify();
@@ -594,7 +594,7 @@ TEST(EngineTest, EventTrackerRegistersAPI) {
 
 TEST(EngineTest, EventTrackerRegistersAssertionFailureRecordAction) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* test_context =
                                           static_cast<engine_test_context*>(context);
                                       test_context->on_engine_running.Notify();
@@ -634,7 +634,7 @@ TEST(EngineTest, EventTrackerRegistersAssertionFailureRecordAction) {
 
 TEST(EngineTest, EventTrackerRegistersEnvoyBugRecordAction) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* test_context =
                                           static_cast<engine_test_context*>(context);
                                       test_context->on_engine_running.Notify();
@@ -674,7 +674,7 @@ TEST(EngineTest, EventTrackerRegistersEnvoyBugRecordAction) {
 
 TEST(MainInterfaceTest, ResetConnectivityState) {
   engine_test_context test_context{};
-  envoy_engine_callbacks engine_cbs{[](void* context) -> void {
+  envoy_engine_callbacks engine_cbs{[](envoy_engine_t, void* context) -> void {
                                       auto* engine_running =
                                           static_cast<engine_test_context*>(context);
                                       engine_running->on_engine_running.Notify();
diff --git a/test/java/integration/AndroidEnvoyExplicitFlowTest.java b/test/java/integration/AndroidEnvoyExplicitFlowTest.java
index 09f2e50675..08a8a63bf9 100644
--- a/test/java/integration/AndroidEnvoyExplicitFlowTest.java
+++ b/test/java/integration/AndroidEnvoyExplicitFlowTest.java
@@ -62,7 +62,7 @@ public void setUpEngine() throws Exception {
     Context appContext = ApplicationProvider.getApplicationContext();
     engine = new AndroidEngineBuilder(appContext)
                  .addLogLevel(LogLevel.OFF)
-                 .setOnEngineRunning(() -> {
+                 .setOnEngineRunning((ignored) -> {
                    latch.countDown();
                    return null;
                  })
diff --git a/test/java/integration/AndroidEnvoyFlowTest.java b/test/java/integration/AndroidEnvoyFlowTest.java
index 7d1bf250c9..c78e3a583f 100644
--- a/test/java/integration/AndroidEnvoyFlowTest.java
+++ b/test/java/integration/AndroidEnvoyFlowTest.java
@@ -58,7 +58,7 @@ public void setUpEngine() throws Exception {
     CountDownLatch latch = new CountDownLatch(1);
     Context appContext = ApplicationProvider.getApplicationContext();
     engine = new AndroidEngineBuilder(appContext)
-                 .setOnEngineRunning(() -> {
+                 .setOnEngineRunning((ignored) -> {
                    latch.countDown();
                    return null;
                  })
diff --git a/test/java/io/envoyproxy/envoymobile/engine/testing/QuicTestServerTest.java b/test/java/io/envoyproxy/envoymobile/engine/testing/QuicTestServerTest.java
index 1c2d630186..4029d1f7cc 100644
--- a/test/java/io/envoyproxy/envoymobile/engine/testing/QuicTestServerTest.java
+++ b/test/java/io/envoyproxy/envoymobile/engine/testing/QuicTestServerTest.java
@@ -110,7 +110,7 @@ public void setUpEngine() throws Exception {
     engine = new AndroidEngineBuilder(
                  appContext, new Custom(String.format(CONFIG, QuicTestServer.getServerPort())))
                  .addLogLevel(LogLevel.WARN)
-                 .setOnEngineRunning(() -> {
+                 .setOnEngineRunning((ignored) -> {
                    latch.countDown();
                    return null;
                  })
diff --git a/test/java/org/chromium/net/testing/AndroidEnvoyExplicitH2FlowTest.java b/test/java/org/chromium/net/testing/AndroidEnvoyExplicitH2FlowTest.java
index 1582cabbab..6eb31f4576 100644
--- a/test/java/org/chromium/net/testing/AndroidEnvoyExplicitH2FlowTest.java
+++ b/test/java/org/chromium/net/testing/AndroidEnvoyExplicitH2FlowTest.java
@@ -45,7 +45,7 @@ public void setUpEngine() throws Exception {
     engine = new AndroidEngineBuilder(appContext)
                  .setTrustChainVerification(ACCEPT_UNTRUSTED)
                  .addLogLevel(LogLevel.DEBUG)
-                 .setOnEngineRunning(() -> {
+                 .setOnEngineRunning((ignored) -> {
                    latch.countDown();
                    return null;
                  })
diff --git a/test/java/org/chromium/net/testing/Http2TestServerTest.java b/test/java/org/chromium/net/testing/Http2TestServerTest.java
index 2ed95a0773..c19a39b27d 100644
--- a/test/java/org/chromium/net/testing/Http2TestServerTest.java
+++ b/test/java/org/chromium/net/testing/Http2TestServerTest.java
@@ -49,7 +49,7 @@ public void setUpEngine() throws Exception {
     Context appContext = ApplicationProvider.getApplicationContext();
     engine = new AndroidEngineBuilder(appContext)
                  .setTrustChainVerification(ACCEPT_UNTRUSTED)
-                 .setOnEngineRunning(() -> {
+                 .setOnEngineRunning((ignored) -> {
                    latch.countDown();
                    return null;
                  })
diff --git a/test/kotlin/io/envoyproxy/envoymobile/EngineBuilderTest.kt b/test/kotlin/io/envoyproxy/envoymobile/EngineBuilderTest.kt
index 56ba5af789..f05e6425fd 100644
--- a/test/kotlin/io/envoyproxy/envoymobile/EngineBuilderTest.kt
+++ b/test/kotlin/io/envoyproxy/envoymobile/EngineBuilderTest.kt
@@ -26,7 +26,7 @@ class EngineBuilderTest {
     engineBuilder.addGrpcStatsDomain("stats.envoyproxy.io")
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.grpcStatsDomain).isEqualTo("stats.envoyproxy.io")
+    assertThat(engine.envoyConfiguration.grpcStatsDomain).isEqualTo("stats.envoyproxy.io")
   }
 
   @Test
@@ -36,7 +36,7 @@ class EngineBuilderTest {
     engineBuilder.enableAdminInterface()
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.adminInterfaceEnabled).isTrue()
+    assertThat(engine.envoyConfiguration.adminInterfaceEnabled).isTrue()
   }
 
   @Test
@@ -46,7 +46,7 @@ class EngineBuilderTest {
     engineBuilder.enableHappyEyeballs(true)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.enableHappyEyeballs).isTrue()
+    assertThat(engine.envoyConfiguration.enableHappyEyeballs).isTrue()
   }
 
   @Test
@@ -56,7 +56,7 @@ class EngineBuilderTest {
     engineBuilder.enableInterfaceBinding(true)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.enableInterfaceBinding).isTrue()
+    assertThat(engine.envoyConfiguration.enableInterfaceBinding).isTrue()
   }
 
   @Test
@@ -66,7 +66,7 @@ class EngineBuilderTest {
     engineBuilder.addConnectTimeoutSeconds(1234)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.connectTimeoutSeconds).isEqualTo(1234)
+    assertThat(engine.envoyConfiguration.connectTimeoutSeconds).isEqualTo(1234)
   }
 
   @Test
@@ -76,7 +76,7 @@ class EngineBuilderTest {
     engineBuilder.addDNSMinRefreshSeconds(1234)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.dnsMinRefreshSeconds).isEqualTo(1234)
+    assertThat(engine.envoyConfiguration.dnsMinRefreshSeconds).isEqualTo(1234)
   }
 
   @Test
@@ -86,7 +86,7 @@ class EngineBuilderTest {
     engineBuilder.addDNSRefreshSeconds(1234)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.dnsRefreshSeconds).isEqualTo(1234)
+    assertThat(engine.envoyConfiguration.dnsRefreshSeconds).isEqualTo(1234)
   }
 
   @Test
@@ -96,8 +96,8 @@ class EngineBuilderTest {
     engineBuilder.addDNSFailureRefreshSeconds(1234, 5678)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.dnsFailureRefreshSecondsBase).isEqualTo(1234)
-    assertThat(engine.envoyConfiguration!!.dnsFailureRefreshSecondsMax).isEqualTo(5678)
+    assertThat(engine.envoyConfiguration.dnsFailureRefreshSecondsBase).isEqualTo(1234)
+    assertThat(engine.envoyConfiguration.dnsFailureRefreshSecondsMax).isEqualTo(5678)
   }
 
   @Test
@@ -107,7 +107,7 @@ class EngineBuilderTest {
     engineBuilder.addDNSQueryTimeoutSeconds(1234)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.dnsQueryTimeoutSeconds).isEqualTo(1234)
+    assertThat(engine.envoyConfiguration.dnsQueryTimeoutSeconds).isEqualTo(1234)
   }
 
   @Test
@@ -117,7 +117,7 @@ class EngineBuilderTest {
     engineBuilder.addDNSFallbackNameservers(listOf<String>("8.8.8.8"))
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.dnsFallbackNameservers.size).isEqualTo(1)
+    assertThat(engine.envoyConfiguration.dnsFallbackNameservers.size).isEqualTo(1)
   }
 
   @Test
@@ -127,7 +127,7 @@ class EngineBuilderTest {
     engineBuilder.enableDNSFilterUnroutableFamilies(true)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.dnsFilterUnroutableFamilies).isTrue()
+    assertThat(engine.envoyConfiguration.dnsFilterUnroutableFamilies).isTrue()
   }
 
   @Test
@@ -137,7 +137,7 @@ class EngineBuilderTest {
     engineBuilder.addH2ConnectionKeepaliveIdleIntervalMilliseconds(1234)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.h2ConnectionKeepaliveIdleIntervalMilliseconds).isEqualTo(1234)
+    assertThat(engine.envoyConfiguration.h2ConnectionKeepaliveIdleIntervalMilliseconds).isEqualTo(1234)
   }
 
   @Test
@@ -147,7 +147,7 @@ class EngineBuilderTest {
     engineBuilder.addH2ConnectionKeepaliveTimeoutSeconds(1234)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.h2ConnectionKeepaliveTimeoutSeconds).isEqualTo(1234)
+    assertThat(engine.envoyConfiguration.h2ConnectionKeepaliveTimeoutSeconds).isEqualTo(1234)
   }
 
   @Test
@@ -157,7 +157,7 @@ class EngineBuilderTest {
     engineBuilder.setMaxConnectionsPerHost(1234)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.maxConnectionsPerHost).isEqualTo(1234)
+    assertThat(engine.envoyConfiguration.maxConnectionsPerHost).isEqualTo(1234)
   }
 
   @Test
@@ -167,7 +167,7 @@ class EngineBuilderTest {
     engineBuilder.h2ExtendKeepaliveTimeout(true)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.h2ExtendKeepaliveTimeout).isTrue()
+    assertThat(engine.envoyConfiguration.h2ExtendKeepaliveTimeout).isTrue()
   }
 
   @Test
@@ -177,7 +177,7 @@ class EngineBuilderTest {
     engineBuilder.addH2RawDomains(listOf<String>("h2-raw.domain"))
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.h2RawDomains.size).isEqualTo(1)
+    assertThat(engine.envoyConfiguration.h2RawDomains.size).isEqualTo(1)
   }
 
   @Test
@@ -187,7 +187,7 @@ class EngineBuilderTest {
     engineBuilder.addStatsFlushSeconds(1234)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.statsFlushSeconds).isEqualTo(1234)
+    assertThat(engine.envoyConfiguration.statsFlushSeconds).isEqualTo(1234)
   }
 
   @Test
@@ -197,7 +197,7 @@ class EngineBuilderTest {
     engineBuilder.addStreamIdleTimeoutSeconds(1234)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.streamIdleTimeoutSeconds).isEqualTo(1234)
+    assertThat(engine.envoyConfiguration.streamIdleTimeoutSeconds).isEqualTo(1234)
   }
 
   @Test
@@ -207,7 +207,7 @@ class EngineBuilderTest {
     engineBuilder.addPerTryIdleTimeoutSeconds(5678)
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.perTryIdleTimeoutSeconds).isEqualTo(5678)
+    assertThat(engine.envoyConfiguration.perTryIdleTimeoutSeconds).isEqualTo(5678)
   }
 
   @Test
@@ -217,7 +217,7 @@ class EngineBuilderTest {
     engineBuilder.addAppVersion("v1.2.3")
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.appVersion).isEqualTo("v1.2.3")
+    assertThat(engine.envoyConfiguration.appVersion).isEqualTo("v1.2.3")
   }
 
   @Test
@@ -227,7 +227,7 @@ class EngineBuilderTest {
     engineBuilder.addAppId("com.envoymobile.android")
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.appId).isEqualTo("com.envoymobile.android")
+    assertThat(engine.envoyConfiguration.appId).isEqualTo("com.envoymobile.android")
   }
 
   @Test
@@ -237,7 +237,7 @@ class EngineBuilderTest {
     engineBuilder.addVirtualClusters("[test]")
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.virtualClusters).isEqualTo("[test]")
+    assertThat(engine.envoyConfiguration.virtualClusters).isEqualTo("[test]")
   }
 
   @Test
@@ -247,6 +247,6 @@ class EngineBuilderTest {
     engineBuilder.addNativeFilter("name", "config")
 
     val engine = engineBuilder.build() as EngineImpl
-    assertThat(engine.envoyConfiguration!!.nativeFilterChain.size).isEqualTo(1)
+    assertThat(engine.envoyConfiguration.nativeFilterChain.size).isEqualTo(1)
   }
 }
diff --git a/test/swift/apps/baseline/ViewController.swift b/test/swift/apps/baseline/ViewController.swift
index 8676c01002..2618478054 100644
--- a/test/swift/apps/baseline/ViewController.swift
+++ b/test/swift/apps/baseline/ViewController.swift
@@ -24,7 +24,7 @@ final class ViewController: UITableViewController {
       .addPlatformFilter(AsyncDemoFilter.init)
       // swiftlint:disable:next line_length
       .addNativeFilter(name: "envoy.filters.http.buffer", typedConfig: "{\"@type\":\"type.googleapis.com/envoy.extensions.filters.http.buffer.v3.Buffer\",\"max_request_bytes\":5242880}")
-      .setOnEngineRunning { NSLog("Envoy async internal setup completed") }
+      .setOnEngineRunning { _ in NSLog("Envoy async internal setup completed") }
       .addStringAccessor(name: "demo-accessor", accessor: { return "PlatformString" })
       .setEventTracker { NSLog("Envoy event emitted: \($0)") }
       .build()
diff --git a/test/swift/apps/experimental/ViewController.swift b/test/swift/apps/experimental/ViewController.swift
index 59644895ed..7af1ce9c23 100644
--- a/test/swift/apps/experimental/ViewController.swift
+++ b/test/swift/apps/experimental/ViewController.swift
@@ -26,7 +26,7 @@ final class ViewController: UITableViewController {
       .enableInterfaceBinding(true)
       // swiftlint:disable:next line_length
       .addNativeFilter(name: "envoy.filters.http.buffer", typedConfig: "{\"@type\":\"type.googleapis.com/envoy.extensions.filters.http.buffer.v3.Buffer\",\"max_request_bytes\":5242880}")
-      .setOnEngineRunning { NSLog("Envoy async internal setup completed") }
+      .setOnEngineRunning { _ in NSLog("Envoy async internal setup completed") }
       .addStringAccessor(name: "demo-accessor", accessor: { return "PlatformString" })
       .setEventTracker { NSLog("Envoy event emitted: \($0)") }
       .build()
diff --git a/test/swift/integration/EngineApiTest.swift b/test/swift/integration/EngineApiTest.swift
index d81d626213..ffc10bc34f 100644
--- a/test/swift/integration/EngineApiTest.swift
+++ b/test/swift/integration/EngineApiTest.swift
@@ -9,7 +9,9 @@ final class EngineApiTest: XCTestCase {
     let engine = EngineBuilder()
       .addLogLevel(.debug)
       .addStatsFlushSeconds(1)
-      .setOnEngineRunning {
+      .setOnEngineRunning { engineHandle in
+        // TODO(jpsim): Update this check when the engine singleton is removed
+        XCTAssertEqual(engineHandle, 1)
         engineExpectation.fulfill()
       }
       .build()
diff --git a/test/swift/integration/SetLoggerTest.swift b/test/swift/integration/SetLoggerTest.swift
index f9c7aa729b..161ec23f07 100644
--- a/test/swift/integration/SetLoggerTest.swift
+++ b/test/swift/integration/SetLoggerTest.swift
@@ -69,7 +69,7 @@ static_resources:
           loggingExpectation.fulfill()
         }
       }
-      .setOnEngineRunning {
+      .setOnEngineRunning { _ in
         engineExpectation.fulfill()
       }
       .setEventTracker { event in
diff --git a/test/swift/integration/StatFlushIntegrationTest.swift b/test/swift/integration/StatFlushIntegrationTest.swift
index 519116a4e4..ba579e352c 100644
--- a/test/swift/integration/StatFlushIntegrationTest.swift
+++ b/test/swift/integration/StatFlushIntegrationTest.swift
@@ -9,7 +9,7 @@ final class StatFlushIntegrationTest: XCTestCase {
     let engine = EngineBuilder()
       .addLogLevel(.debug)
       .addStatsFlushSeconds(1)
-      .setOnEngineRunning {
+      .setOnEngineRunning { _ in
         engineExpectation.fulfill()
       }
       .build()