diff --git a/.changeset/v6-posthog-ios-4.md b/.changeset/v6-posthog-ios-4.md
new file mode 100644
index 00000000..39b171fa
--- /dev/null
+++ b/.changeset/v6-posthog-ios-4.md
@@ -0,0 +1,8 @@
+---
+"posthog_flutter": major
+---
+
+- **Breaking:** adopt `posthog-ios` 4.x, which requires Xcode 26
+- **Breaking:** return `null` instead of the raw string for a malformed, empty, or whitespace-only `getFeatureFlagResult()` payload on iOS and macOS
+- **Breaking:** keep string payloads passed to `PostHogBootstrapConfig.featureFlagPayloads`, such as `"123"`, as strings on iOS and macOS instead of decoding them to numbers or booleans
+- **Breaking:** stop sending the legacy `version` and `build` properties on `Application Installed`, `Application Updated` and `Application Opened` on iOS and macOS — use `$app_version` and `$app_build`. Android still sends them until `posthog-android` drops them
diff --git a/posthog_flutter/darwin/posthog_flutter.podspec b/posthog_flutter/darwin/posthog_flutter.podspec
index 98e3a7cf..d50d58d6 100644
--- a/posthog_flutter/darwin/posthog_flutter.podspec
+++ b/posthog_flutter/darwin/posthog_flutter.podspec
@@ -21,7 +21,7 @@ Postog flutter plugin
   s.ios.dependency 'Flutter'
   s.osx.dependency 'FlutterMacOS'
 
-  s.dependency 'PostHog', '>= 3.84.0', '< 4.0.0'
+  s.dependency 'PostHog', '>= 4.0.0', '< 5.0.0'
 
   s.ios.deployment_target = '15.0'
   s.osx.deployment_target = '11.0'
diff --git a/posthog_flutter/darwin/posthog_flutter/Package.swift b/posthog_flutter/darwin/posthog_flutter/Package.swift
index 1cf4470c..5d2d9474 100644
--- a/posthog_flutter/darwin/posthog_flutter/Package.swift
+++ b/posthog_flutter/darwin/posthog_flutter/Package.swift
@@ -14,7 +14,7 @@ let package = Package(
     ],
     dependencies: [
         .package(name: "FlutterFramework", path: "../FlutterFramework"),
-        .package(url: "https://github.com/PostHog/posthog-ios", "3.84.0" ..< "4.0.0"),
+        .package(url: "https://github.com/PostHog/posthog-ios", "4.0.0" ..< "5.0.0"),
     ],
     targets: [
         .target(
diff --git a/posthog_flutter/darwin/posthog_flutter/Sources/posthog_flutter/PosthogFlutterPlugin.swift b/posthog_flutter/darwin/posthog_flutter/Sources/posthog_flutter/PosthogFlutterPlugin.swift
index a69380be..a99dd547 100644
--- a/posthog_flutter/darwin/posthog_flutter/Sources/posthog_flutter/PosthogFlutterPlugin.swift
+++ b/posthog_flutter/darwin/posthog_flutter/Sources/posthog_flutter/PosthogFlutterPlugin.swift
@@ -1540,7 +1540,7 @@ extension PosthogFlutterPlugin {
     private func reloadFeatureFlags(_ result: @escaping FlutterResult) {
         // Resolve the Dart Future only once flags have actually finished loading.
         // The native callback fires on a background thread, so hop to main for Flutter.
-        PostHogSDK.shared.reloadFeatureFlags {
+        PostHogSDK.shared.reloadFeatureFlags { _ in
             DispatchQueue.main.async {
                 result(nil)
             }