diff --git a/build/rbe/rewrapper_dart.py b/build/rbe/rewrapper_dart.py
index 76b753dd7cb..40e4f4952cb 100644
--- a/build/rbe/rewrapper_dart.py
+++ b/build/rbe/rewrapper_dart.py
@@ -82,7 +82,7 @@ def list_imports(uri, exec_root, package_config):
         ]:
             continue
         # Imports must happen before definitions.
-        if tokens[0] in ['const', 'class', 'enum']:
+        if tokens[0] in ['const', 'class', 'enum', 'final']:
             break
         if 2 <= len(tokens
                    ) and tokens[0] == 'if' and tokens[1] == '(dart.library.io)':
diff --git a/pkg/dart2wasm/lib/compile.dart b/pkg/dart2wasm/lib/compile.dart
index 61dd17addc6..b3dfa7f9a0f 100644
--- a/pkg/dart2wasm/lib/compile.dart
+++ b/pkg/dart2wasm/lib/compile.dart
@@ -48,8 +48,9 @@ sealed class CompilationResult {}
 class CompilationSuccess extends CompilationResult {
   final Map<String, ({Uint8List moduleBytes, String? sourceMap})> wasmModules;
   final String jsRuntime;
+  final String supportJs;
 
-  CompilationSuccess(this.wasmModules, this.jsRuntime);
+  CompilationSuccess(this.wasmModules, this.jsRuntime, this.supportJs);
 }
 
 class CompilationError extends CompilationResult {}
@@ -238,11 +239,8 @@ Future<CompilationResult> compileToModule(
 
   String? depFile = options.depFile;
   if (depFile != null) {
-    writeDepfile(
-        compilerOptions.fileSystem,
-        component.uriToSource.keys,
-        options.outputFile,
-        depFile);
+    writeDepfile(compilerOptions.fileSystem, component.uriToSource.keys,
+        options.outputFile, depFile);
   }
 
   final generateSourceMaps = options.translatorOptions.generateSourceMaps;
@@ -262,7 +260,50 @@ Future<CompilationResult> compileToModule(
   String jsRuntime = jsRuntimeFinalizer.generate(
       translator.functions.translatedProcedures,
       translator.internalizedStringsForJSRuntime,
+      translator.options.requireJsStringBuiltin,
       mode);
 
-  return CompilationSuccess(wasmModules, jsRuntime);
+  final supportJs = _generateSupportJs(options.translatorOptions);
+  return CompilationSuccess(wasmModules, jsRuntime, supportJs);
+}
+
+String _generateSupportJs(TranslatorOptions options) {
+  // Copied from
+  // https://github.com/GoogleChromeLabs/wasm-feature-detect/blob/main/src/detectors/gc/index.js
+  //
+  // Uses WasmGC types and will only validate correctly if the engine supports
+  // WasmGC:
+  // ```
+  //     (module
+  //       (type $type0 (struct (field $field0 i8)))
+  //     )
+  // ```
+  //
+  // NOTE: Once we support more feature detections we may use
+  // `package:wasm_builder` to create the module instead of having a fixed one
+  // here.
+  const String supportsWasmGC =
+      'WebAssembly.validate(new Uint8Array([0,97,115,109,1,0,0,0,1,5,1,95,1,120,0]))';
+
+  // Imports a `js-string` builtin spec function *with wrong signature*. An engine
+  //
+  //   * *without* knowledge about `js-string` builtin would accept such an import at
+  //     validation time.
+  //
+  //   * *with* knowledge about `js-string` would refuse it as the signature
+  //   used to import the `cast` function is not according to `js-string` spec
+  //
+  //  ```
+  //     (module
+  //     (func $wasm:js-string.cast (;0;) (import "wasm:js-string" "cast"))
+  //     )
+  // ```
+  const String supportsJsStringBuiltins =
+      '!WebAssembly.validate(new Uint8Array([0,97,115,109,1,0,0,0,1,4,1,96,0,0,2,23,1,14,119,97,115,109,58,106,115,45,115,116,114,105,110,103,4,99,97,115,116,0,0]),{"builtins":["js-string"]})';
+
+  final requiredFeatures = [
+    supportsWasmGC,
+    if (options.requireJsStringBuiltin) supportsJsStringBuiltins
+  ];
+  return '(${requiredFeatures.join('&&')})';
 }
diff --git a/pkg/dart2wasm/lib/compiler_options.dart b/pkg/dart2wasm/lib/compiler_options.dart
index fa526289737..da74fdc84d8 100644
--- a/pkg/dart2wasm/lib/compiler_options.dart
+++ b/pkg/dart2wasm/lib/compiler_options.dart
@@ -15,7 +15,6 @@ class WasmCompilerOptions {
   Uri mainUri;
   String outputFile;
   String? depFile;
-  String? outputJSRuntimeFile;
   Uri? dynamicModuleMainUri;
   Uri? dynamicInterfaceUri;
   Uri? dynamicModuleMetadataFile;
diff --git a/pkg/dart2wasm/lib/dart2wasm.dart b/pkg/dart2wasm/lib/dart2wasm.dart
index 352b3a9d3fe..9cb8c5a3f61 100644
--- a/pkg/dart2wasm/lib/dart2wasm.dart
+++ b/pkg/dart2wasm/lib/dart2wasm.dart
@@ -78,8 +78,6 @@ final List<Option> options = [
   StringMultiOption("delete-tostring-package-uri",
       (o, values) => o.deleteToStringPackageUri = values),
   StringOption("depfile", (o, value) => o.depFile = value),
-  StringOption(
-      "js-runtime-output", (o, value) => o.outputJSRuntimeFile = value),
   StringOption(
       "dump-kernel-after-cfe", (o, value) => o.dumpKernelAfterCfe = value,
       hide: true),
@@ -99,6 +97,9 @@ final List<Option> options = [
   Flag("enable-deferred-loading",
       (o, value) => o.translatorOptions.enableDeferredLoading = value,
       defaultsTo: _d.translatorOptions.enableDeferredLoading),
+  Flag("require-js-string-builtin",
+      (o, value) => o.translatorOptions.requireJsStringBuiltin = value,
+      defaultsTo: _d.translatorOptions.requireJsStringBuiltin),
   Flag("enable-multi-module-stress-test-mode",
       (o, value) => o.translatorOptions.enableMultiModuleStressTestMode = value,
       defaultsTo: _d.translatorOptions.enableMultiModuleStressTestMode),
diff --git a/pkg/dart2wasm/lib/generate_wasm.dart b/pkg/dart2wasm/lib/generate_wasm.dart
index 12c89b9ad1d..09986a62334 100644
--- a/pkg/dart2wasm/lib/generate_wasm.dart
+++ b/pkg/dart2wasm/lib/generate_wasm.dart
@@ -113,9 +113,11 @@ Future<int> generateWasm(WasmCompilerOptions options,
   });
   await Future.wait(writeFutures);
 
-  final jsFile = options.outputJSRuntimeFile ??
-      path.setExtension(options.outputFile, '.mjs');
+  final jsFile = path.setExtension(options.outputFile, '.mjs');
   await File(jsFile).writeAsString(result.jsRuntime);
 
+  final supportJsFile = path.setExtension(options.outputFile, '.support.js');
+  await File(supportJsFile).writeAsString(result.supportJs);
+
   return 0;
 }
diff --git a/pkg/dart2wasm/lib/js/runtime_blob.dart b/pkg/dart2wasm/lib/js/runtime_blob.dart
index 76697fbb615..aab2fd2b03f 100644
--- a/pkg/dart2wasm/lib/js/runtime_blob.dart
+++ b/pkg/dart2wasm/lib/js/runtime_blob.dart
@@ -2,15 +2,14 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-const jsRuntimeBlobPart1 = r'''
-
+final jsRuntimeBlobTemplate = Template(r'''
 // Compiles a dart2wasm-generated main module from `source` which can then
 // instantiatable via the `instantiate` method.
 //
 // `source` needs to be a `Response` object (or promise thereof) e.g. created
 // via the `fetch()` JS API.
 export async function compileStreaming(source) {
-  const builtins = {builtins: ['js-string']};
+  const builtins = {<<BUILTINS_MAP_BODY>>};
   return new CompiledApp(
       await WebAssembly.compileStreaming(source, builtins), builtins);
 }
@@ -18,7 +17,7 @@ export async function compileStreaming(source) {
 // Compiles a dart2wasm-generated wasm modules from `bytes` which is then
 // instantiatable via the `instantiate` method.
 export async function compile(bytes) {
-  const builtins = {builtins: ['js-string']};
+  const builtins = {<<BUILTINS_MAP_BODY>>};
   return new CompiledApp(await WebAssembly.compile(bytes, builtins), builtins);
 }
 
@@ -97,27 +96,65 @@ class CompiledApp {
 
     // Imports
     const dart2wasm = {
-''';
-
-// We break inside the 'dart2wasm' object to enable injection of methods. We
-// could use interpolation, but then we'd have to escape characters.
-const jsRuntimeBlobPart2 = r'''
+      <<JS_METHODS>>
     };
 
     const baseImports = {
       dart2wasm: dart2wasm,
-''';
-
-// We break inside of `baseImports` to inject internalized strings.
-const jsRuntimeBlobPart3 = r'''
       Math: Math,
       Date: Date,
       Object: Object,
       Array: Array,
       Reflect: Reflect,
+      <<IMPORTED_JS_STRINGS_IN_MJS>>
     };
 
-    const jsStringPolyfill = {
+    <<JS_STRING_POLYFILL_METHODS>>
+
+    const deferredLibraryHelper = {
+      "loadModule": async (moduleName) => {
+        if (!loadDeferredWasm) {
+          throw "No implementation of loadDeferredWasm provided.";
+        }
+        const source = await Promise.resolve(loadDeferredWasm(moduleName));
+        const module = await ((source instanceof Response)
+            ? WebAssembly.compileStreaming(source, this.builtins)
+            : WebAssembly.compile(source, this.builtins));
+        return await WebAssembly.instantiate(module, {
+          ...baseImports,
+          ...additionalImports,
+          <<JS_POLYFILL_IMPORT>>
+          "module0": dartInstance.exports,
+        });
+      },
+    };
+
+    dartInstance = await WebAssembly.instantiate(this.module, {
+      ...baseImports,
+      ...additionalImports,
+      "deferredLibraryHelper": deferredLibraryHelper,
+      <<JS_POLYFILL_IMPORT>>
+    });
+
+    return new InstantiatedApp(this, dartInstance);
+  }
+}
+
+class InstantiatedApp {
+  constructor(compiledApp, instantiatedModule) {
+    this.compiledApp = compiledApp;
+    this.instantiatedModule = instantiatedModule;
+  }
+
+  // Call the main function with the given arguments.
+  invokeMain(...args) {
+    this.instantiatedModule.exports.$invokeMain(args);
+  }
+}
+''');
+
+const String jsPolyFillMethods = r'''
+const jsStringPolyfill = {
       "charCodeAt": (s, i) => s.charCodeAt(i),
       "compare": (s1, s2) => {
         if (s1 < s2) return -1;
@@ -150,45 +187,53 @@ const jsRuntimeBlobPart3 = r'''
         return result;
       },
     };
-
-    const deferredLibraryHelper = {
-      "loadModule": async (moduleName) => {
-        if (!loadDeferredWasm) {
-          throw "No implementation of loadDeferredWasm provided.";
-        }
-        const source = await Promise.resolve(loadDeferredWasm(moduleName));
-        const module = await ((source instanceof Response)
-            ? WebAssembly.compileStreaming(source, this.builtins)
-            : WebAssembly.compile(source, this.builtins));
-        return await WebAssembly.instantiate(module, {
-          ...baseImports,
-          ...additionalImports,
-          "wasm:js-string": jsStringPolyfill,
-          "module0": dartInstance.exports,
-        });
-      },
-    };
-
-    dartInstance = await WebAssembly.instantiate(this.module, {
-      ...baseImports,
-      ...additionalImports,
-      "deferredLibraryHelper": deferredLibraryHelper,
-      "wasm:js-string": jsStringPolyfill,
-    });
-
-    return new InstantiatedApp(this, dartInstance);
-  }
-}
-
-class InstantiatedApp {
-  constructor(compiledApp, instantiatedModule) {
-    this.compiledApp = compiledApp;
-    this.instantiatedModule = instantiatedModule;
-  }
-
-  // Call the main function with the given arguments.
-  invokeMain(...args) {
-    this.instantiatedModule.exports.$invokeMain(args);
-  }
-}
 ''';
+
+class Template {
+  static final _templateVariableRegExp = RegExp(r'<<(?<varname>[A-Z_]+)>>');
+  final List<_TemplatePart> _parts = [];
+
+  Template(String stringTemplate) {
+    int offset = 0;
+    for (final match in _templateVariableRegExp.allMatches(stringTemplate)) {
+      _parts.add(
+          _TemplateStringPart(stringTemplate.substring(offset, match.start)));
+      _parts.add(_TemplateVariablePart(match.namedGroup('varname')!));
+      offset = match.end;
+    }
+    _parts.add(_TemplateStringPart(
+        stringTemplate.substring(offset, stringTemplate.length)));
+  }
+
+  String instantiate(Map<String, String> variableValues) {
+    final sb = StringBuffer();
+    for (final part in _parts) {
+      sb.write(part.instantiate(variableValues));
+    }
+    return sb.toString();
+  }
+}
+
+abstract class _TemplatePart {
+  String instantiate(Map<String, String> variableValues);
+}
+
+class _TemplateStringPart extends _TemplatePart {
+  final String string;
+  _TemplateStringPart(this.string);
+
+  @override
+  String instantiate(Map<String, String> variableValues) => string;
+}
+
+class _TemplateVariablePart extends _TemplatePart {
+  final String variable;
+  _TemplateVariablePart(this.variable);
+
+  @override
+  String instantiate(Map<String, String> variableValues) {
+    final value = variableValues[variable];
+    if (value != null) return value;
+    throw 'Template contains no value for variable $variable';
+  }
+}
diff --git a/pkg/dart2wasm/lib/js/runtime_generator.dart b/pkg/dart2wasm/lib/js/runtime_generator.dart
index 7506f8dbb5c..8756e8c7726 100644
--- a/pkg/dart2wasm/lib/js/runtime_generator.dart
+++ b/pkg/dart2wasm/lib/js/runtime_generator.dart
@@ -54,8 +54,11 @@ class RuntimeFinalizer {
 
   RuntimeFinalizer(this.allJSMethods);
 
-  String generate(Iterable<Procedure> translatedProcedures,
-      List<String> constantStrings, wasm_target.Mode mode) {
+  String generate(
+      Iterable<Procedure> translatedProcedures,
+      List<String> constantStrings,
+      bool requireJsBuiltin,
+      wasm_target.Mode mode) {
     String escape(String s) => json.encode(s);
 
     Set<Procedure> usedProcedures = {};
@@ -87,6 +90,11 @@ class RuntimeFinalizer {
       }
     }
 
+    final builtins = [
+      'builtins: [\'js-string\']',
+      if (requireJsBuiltin) 'importedStringConstants: \'S\'',
+    ];
+
     String internalizedStrings = '';
     if (constantStrings.isNotEmpty) {
       internalizedStrings = '''
@@ -95,13 +103,15 @@ class RuntimeFinalizer {
       ],
 ''';
     }
-    return '''
-$jsRuntimeBlobPart1
-$jsMethods
-$jsRuntimeBlobPart2
-$internalizedStrings
-$jsRuntimeBlobPart3
-''';
+
+    return jsRuntimeBlobTemplate.instantiate({
+      'BUILTINS_MAP_BODY': builtins.join(', '),
+      'JS_METHODS': jsMethods.toString(),
+      'IMPORTED_JS_STRINGS_IN_MJS': internalizedStrings,
+      'JS_STRING_POLYFILL_METHODS': requireJsBuiltin ? '' : jsPolyFillMethods,
+      'JS_POLYFILL_IMPORT':
+          requireJsBuiltin ? '' : '"wasm:js-string": jsStringPolyfill,'
+    });
   }
 }
 
diff --git a/pkg/dart2wasm/lib/translator.dart b/pkg/dart2wasm/lib/translator.dart
index 871dc478552..0753d20e12c 100644
--- a/pkg/dart2wasm/lib/translator.dart
+++ b/pkg/dart2wasm/lib/translator.dart
@@ -55,6 +55,7 @@ class TranslatorOptions {
   bool enableMultiModuleStressTestMode = false;
   int inliningLimit = 0;
   int? sharedMemoryMaxPages;
+  bool requireJsStringBuiltin = false;
   List<int> watchPoints = [];
 }
 
@@ -1601,11 +1602,39 @@ class Translator with KernelNodes {
     if (internalizedString != null) {
       return internalizedString;
     }
-    final i = internalizedStringsForJSRuntime.length;
-    internalizedString = module.globals.import('s', '$i',
-        w.GlobalType(w.RefType.extern(nullable: true), mutable: false));
+    bool hasUnpairedSurrogate(String str) {
+      for (int i = 0; i < str.length; i++) {
+        int codeUnit = str.codeUnitAt(i);
+        if (codeUnit >= 0xD800 && codeUnit <= 0xDBFF) {
+          if (i + 1 >= str.length ||
+              str.codeUnitAt(i + 1) < 0xDC00 ||
+              str.codeUnitAt(i + 1) > 0xDFFF) {
+            return true;
+          } else {
+            i++;
+          }
+        } else if (codeUnit >= 0xDC00 && codeUnit <= 0xDFFF) {
+          return true;
+        }
+      }
+      return false;
+    }
+
+    if (!options.requireJsStringBuiltin || hasUnpairedSurrogate(s)) {
+      // Unpaired surrogates can't be encoded as UTF-8, import them from JS
+      // runtime.
+      final i = internalizedStringsForJSRuntime.length;
+      internalizedString = module.globals.import('s', '$i',
+          w.GlobalType(w.RefType.extern(nullable: true), mutable: false));
+      internalizedStringsForJSRuntime.add(s);
+    } else {
+      internalizedString = module.globals.import(
+        'S',
+        s,
+        w.GlobalType(w.RefType.extern(nullable: true), mutable: false),
+      );
+    }
     _internalizedStringGlobals[(module, s)] = internalizedString;
-    internalizedStringsForJSRuntime.add(s);
     return internalizedString;
   }
 }
diff --git a/tools/bots/test_matrix.json b/tools/bots/test_matrix.json
index f482d5bf0e8..1b0fded517b 100644
--- a/tools/bots/test_matrix.json
+++ b/tools/bots/test_matrix.json
@@ -461,7 +461,8 @@
         "host-asserts": true,
         "enable-asserts": true,
         "dart2wasm-options": [
-          "-O0"
+          "-O0",
+          "--extra-compiler-option=--require-js-string-builtin"
         ],
         "timeout": 60
       }