@@ -7,7 +7,29 @@ import { FlutterEntrypointLoader } from './entrypoint_loader.js';
 import { FlutterTrustedTypesPolicy } from './trusted_types.js';
 import { loadCanvasKit } from './canvaskit_loader.js';
 import { loadSkwasm } from './skwasm_loader.js';
-import { getCanvaskitBaseUrl } from './utils.js';
+import { getCanvaskitBaseUrl, resolveUrlWithSegments } from './utils.js';
+
+/**
+ * Fire-and-forget cleanup for legacy `flutter_service_worker.js?v=` registrations
+ * whose script URL may be cached indefinitely by a CDN.
+ *
+ * TODO(kevmoo): Remove in 2027 H2 (https://github.com/flutter/flutter/issues/156910).
+ * @param {TrustedTypePolicy?} ttPolicy
+ */
+function cleanupLegacyServiceWorker(ttPolicy) {
+  if ('serviceWorker' in navigator) {
+    navigator.serviceWorker.getRegistration().then((registration) => {
+      const scriptURL = registration?.active?.scriptURL ?? '';
+      if (scriptURL.includes('flutter_service_worker.js?v=')) {
+        let url = resolveUrlWithSegments(`flutter_service_worker.js?v=${Date.now()}`);
+        if (ttPolicy != null) {
+          url = ttPolicy.createScriptURL(url);
+        }
+        navigator.serviceWorker.register(url);
+      }
+    });
+  }
+}
 
 /**
  * The public interface of _flutter.loader. Exposes two methods:
@@ -27,7 +49,7 @@ export class FlutterLoader {
    */
   async loadEntrypoint(options) {
     const { serviceWorker, ...entrypoint } = options || {};
-    if (serviceWorker) {
+    if (serviceWorker?.serviceWorkerUrl) {
       console.warn(
         'FlutterLoader.loadEntrypoint: The "serviceWorker" option is deprecated and ignored. ' +
         'Register custom service workers directly with navigator.serviceWorker.register(). ' +
@@ -36,6 +58,7 @@ export class FlutterLoader {
     }
     // A Trusted Types policy that is going to be used by the loader.
     const flutterTT = new FlutterTrustedTypesPolicy();
+    cleanupLegacyServiceWorker(flutterTT.policy);
     // The FlutterEntrypointLoader instance could be injected as a dependency
     // (and dynamically imported from a module if not present).
     const entrypointLoader = new FlutterEntrypointLoader();
@@ -63,7 +86,7 @@ export class FlutterLoader {
     config,
     serviceWorkerSettings,
   } = {}) {
-    if (serviceWorkerSettings) {
+    if (serviceWorkerSettings?.serviceWorkerUrl) {
       console.warn(
         'FlutterLoader.load: The "serviceWorkerSettings" option is deprecated and ignored. ' +
         'Register custom service workers directly with navigator.serviceWorker.register(). ' +
@@ -160,6 +183,7 @@ export class FlutterLoader {
 
     const deps = {};
     deps.flutterTT = new FlutterTrustedTypesPolicy();
+    cleanupLegacyServiceWorker(deps.flutterTT.policy);
 
     const canvasKitBaseUrl = getCanvaskitBaseUrl(config, buildConfig);
     if (build.renderer === "canvaskit") {
 
@@ -136,11 +136,6 @@ class WebTemplate {
       newContent = newContent.replaceAll(kStaticAssetsUrlPlaceholder, staticAssetsUrl);
     }
 
-    newContent = newContent.replaceFirst(
-      // Support older `var` syntax as well as new `const` syntax
-      RegExp('(const|var) serviceWorkerVersion = null'),
-      'const serviceWorkerVersion = null /* $_kServiceWorkerDeprecationNotice */',
-    );
     newContent = _applyVariableSubstitutions(newContent, logger, <String, String>{
       ...webDefines,
       'flutter_build_config': ?buildConfig,
 
@@ -198,7 +198,7 @@ String htmlSample2Replaced({required String baseHref}) =>
   <div></div>
   <script src="main.dart.js"></script>
   <script>
-    const serviceWorkerVersion = null /* Flutter's service worker is deprecated and has been removed. */;
+    const serviceWorkerVersion = null;
   </script>
   <script>
     navigator.serviceWorker.register('flutter_service_worker.js');
@@ -321,14 +321,6 @@ void main() {
     );
   });
 
-  test('applies substitutions with legacy var version syntax', () {
-    const indexHtml = WebTemplate(htmlSampleLegacyVar);
-    expect(
-      indexHtml.withSubstitutions(baseHref: '/foo/333/', flutterJsFile: flutterJs, logger: logger),
-      htmlSample2Replaced(baseHref: '/foo/333/'),
-    );
-  });
-
   test('applies substitutions to inline flutter.js bootstrap script', () {
     const indexHtml = WebTemplate(htmlSampleInlineFlutterJsBootstrap);
     final List<WebTemplateWarning> warnings = indexHtml.getWarnings();