diff --git a/lib/src/isolate_manager.dart b/lib/src/isolate_manager.dart
index edcbe6d..4c5fb3c 100644
--- a/lib/src/isolate_manager.dart
+++ b/lib/src/isolate_manager.dart
@@ -41,6 +41,8 @@ class IsolateManager<R, P> {
     QueueStrategy<R, P>? queueStrategy,
     this.isDebug = false,
   })  : isCustomIsolate = false,
+        // This API will be removed in v6.0.0 when we reach the stable release.
+        // ignore: deprecated_member_use_from_same_package
         initialParams = '',
         queueStrategy = queueStrategy ?? QueueStrategyUnlimited(),
         _workerName = workerName,
@@ -70,6 +72,8 @@ class IsolateManager<R, P> {
   IsolateManager.createCustom(
     IsolateCustomFunction this.isolateFunction, {
     String? workerName,
+    // This API will be removed in v6.0.0 when we reach the stable release.
+    // ignore: deprecated_consistency
     this.initialParams,
     this.concurrent = 1,
     this.converter,
@@ -308,6 +312,9 @@ class IsolateManager<R, P> {
   final String? _workerName;
 
   /// Initial parameters.
+  @Deprecated(
+    'This API will be removed in v6.0.0 when we reach the stable release.',
+  )
   final Object? initialParams;
 
   /// Is using your own isolate function.
@@ -398,6 +405,8 @@ class IsolateManager<R, P> {
             IsolateContactor.createCustom<R, P>(
               isolateFunction as IsolateCustomFunction,
               workerName: workerName,
+              // This API will be removed in v6.0.0 when we reach the stable release.
+              // ignore: deprecated_member_use_from_same_package
               initialParams: initialParams,
               converter: converter,
               workerConverter: workerConverter,
diff --git a/lib/src/isolate_manager_function.dart b/lib/src/isolate_manager_function.dart
index b202ef9..69a2b9a 100644
--- a/lib/src/isolate_manager_function.dart
+++ b/lib/src/isolate_manager_function.dart
@@ -7,11 +7,20 @@ import 'package:isolate_manager/src/isolate_worker/isolate_worker_web.dart'
 
 /// A callback for the [IsolateManagerFunction.customFunction] that will be executed only one time
 /// before all events.
+@Deprecated(
+  'Use `IsolateOnInitCallback` instead. This API will be removed in v6.0.0 when we reach the stable release.',
+)
 typedef IsolateOnInitialCallback<R, P, T> = FutureOr<void> Function(
   IsolateManagerController<R, P> controller,
   T initialParams,
 );
 
+/// A callback for the [IsolateManagerFunction.customFunction] that will be executed only one time
+/// before all events.
+typedef IsolateOnInitCallback<R, P> = FutureOr<void> Function(
+  IsolateManagerController<R, P> controller,
+);
+
 /// A callback for the [IsolateManagerFunction.customFunction] that will be executed only one time
 /// before all events.
 typedef IsolateOnDisposeCallback<R, P> = void Function(
@@ -64,7 +73,11 @@ abstract class IsolateManagerFunction {
     /// A default parameter that used by the package.
     dynamic params, {
     required IsolateOnEventCallback<R, P> onEvent,
+    @Deprecated(
+      ' Use `onInit` instead. This API will be removed in v6.0.0 when we reach the stable release.',
+    )
     IsolateOnInitialCallback<R, P, Object?>? onInitial,
+    IsolateOnInitCallback<R, P>? onInit,
     IsolateOnDisposeCallback<R, P>? onDispose,
     bool autoHandleException = true,
     bool autoHandleResult = true,
@@ -144,9 +157,17 @@ abstract class IsolateManagerFunction {
   /// ```
   static Future<void> workerFunction<R, P>(
     IsolateWorkerFunction<R, P> function, {
+    @Deprecated(
+      'Use `onInit` instead. This API will be removed in v6.0.0 when we reach the stable release.',
+    )
     FutureOr<void> Function()? onInitial,
+    IsolateOnInitCallback<R, P>? onInit,
   }) {
-    return isolateWorkerImpl<R, P>(function, onInitial);
+    assert(
+      onInitial == null || onInit == null,
+      'Provide either `onInit` or `onInitial`, not both.',
+    );
+    return isolateWorkerImpl<R, P>(function, onInitial, onInit);
   }
 
   /// Create a custom Worker function.
diff --git a/lib/src/isolate_worker/isolate_worker_stub.dart b/lib/src/isolate_worker/isolate_worker_stub.dart
index 68aa105..f3f4c18 100644
--- a/lib/src/isolate_worker/isolate_worker_stub.dart
+++ b/lib/src/isolate_worker/isolate_worker_stub.dart
@@ -8,7 +8,11 @@ import 'package:isolate_manager/src/isolate_manager_function.dart';
 /// No-op on `io`.
 Future<void> isolateWorkerImpl<R, P>(
   IsolateWorkerFunction<R, P> function,
+  @Deprecated(
+    'Use `onInit` instead. This API will be removed in v6.0.0 when we reach the stable release.',
+  )
   FutureOr<void> Function()? onInitial,
+  IsolateOnInitCallback<R, P>? onInit,
 ) {
   throw UnimplementedError('Use only on the Web platform to create a Worker');
 }
diff --git a/lib/src/isolate_worker/isolate_worker_web.dart b/lib/src/isolate_worker/isolate_worker_web.dart
index 83dcda8..ccbbfdc 100644
--- a/lib/src/isolate_worker/isolate_worker_web.dart
+++ b/lib/src/isolate_worker/isolate_worker_web.dart
@@ -13,11 +13,16 @@ external DedicatedWorkerGlobalScope get _self;
 /// Create a worker in your `main`.
 Future<void> isolateWorkerImpl<R, P>(
   IsolateWorkerFunction<R, P> function,
+  @Deprecated(
+    'Use `onInit` instead. This API will be removed in v6.0.0 when we reach the stable release.',
+  )
   FutureOr<void> Function()? onInitial,
+  IsolateOnInitCallback<R, P>? onInit,
 ) async {
   final controller = IsolateManagerController<R, P>(_self);
 
   await onInitial?.call();
+  await onInit?.call(controller);
 
   controller.onIsolateMessage.listen((message) async {
     try {
diff --git a/test/isolate_manager_test.dart b/test/isolate_manager_test.dart
index 283d3b4..eced0ee 100644
--- a/test/isolate_manager_test.dart
+++ b/test/isolate_manager_test.dart
@@ -920,10 +920,7 @@ Future<void> isolateFunction(dynamic params) async {
       }
       return 0;
     },
-    onInitial: (
-      IsolateManagerController<int, int> controller,
-      Object? initialParams,
-    ) {},
+    onInit: (IsolateManagerController<int, int> controller) {},
     onDispose: (IsolateManagerController<int, int> controller) {},
     autoHandleException: false,
     autoHandleResult: false,
@@ -937,10 +934,7 @@ void isolateFunctionWithAutomaticallyHandlers(dynamic params) {
     onEvent: (IsolateManagerController<int, int> controller, int message) {
       return fibonacci(message);
     },
-    onInitial: (
-      IsolateManagerController<int, int> controller,
-      Object? initialParams,
-    ) {},
+    onInit: (IsolateManagerController<int, int> controller) {},
     onDispose: (IsolateManagerController<int, int> controller) {},
   );
 }