diff --git a/benchmarks/BigIntParsePrint/dart2/BigIntParsePrint.dart b/benchmarks/BigIntParsePrint/dart2/BigIntParsePrint.dart
index f9e05e7fba4..26a796f3b9c 100644
--- a/benchmarks/BigIntParsePrint/dart2/BigIntParsePrint.dart
+++ b/benchmarks/BigIntParsePrint/dart2/BigIntParsePrint.dart
@@ -4,6 +4,8 @@
 
 // ignore_for_file: avoid_function_literals_in_foreach_calls
 
+// @dart=2.9
+
 import 'package:benchmark_harness/benchmark_harness.dart';
 import 'package:fixnum/fixnum.dart';
 
diff --git a/benchmarks/BigIntParsePrint/dart2/native_version.dart b/benchmarks/BigIntParsePrint/dart2/native_version.dart
index cfc64fafc99..9ca0fa00f70 100644
--- a/benchmarks/BigIntParsePrint/dart2/native_version.dart
+++ b/benchmarks/BigIntParsePrint/dart2/native_version.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 abstract class NativeBigIntMethods {
   bool get enabled;
 
diff --git a/benchmarks/BigIntParsePrint/dart2/native_version_dummy.dart b/benchmarks/BigIntParsePrint/dart2/native_version_dummy.dart
index b3b83ecf43f..9fb7ee62e23 100644
--- a/benchmarks/BigIntParsePrint/dart2/native_version_dummy.dart
+++ b/benchmarks/BigIntParsePrint/dart2/native_version_dummy.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'native_version.dart';
 
 const NativeBigIntMethods nativeBigInt = _DummyMethods();
diff --git a/benchmarks/BigIntParsePrint/dart2/native_version_javascript.dart b/benchmarks/BigIntParsePrint/dart2/native_version_javascript.dart
index e8a6bae3373..37c1eb9b632 100644
--- a/benchmarks/BigIntParsePrint/dart2/native_version_javascript.dart
+++ b/benchmarks/BigIntParsePrint/dart2/native_version_javascript.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 @JS()
 library native_version_javascript;
 
diff --git a/benchmarks/Calls/dart2/Calls.dart b/benchmarks/Calls/dart2/Calls.dart
index 5b94b2a56de..32cc0dd7da1 100644
--- a/benchmarks/Calls/dart2/Calls.dart
+++ b/benchmarks/Calls/dart2/Calls.dart
@@ -4,6 +4,8 @@
 
 // Micro-benchmarks for sync/sync*/async/async* functionality.
 
+// @dart=2.9
+
 import 'dart:async';
 
 const int iterationLimitAsync = 200;
diff --git a/benchmarks/Dynamic/dart2/Dynamic.dart b/benchmarks/Dynamic/dart2/Dynamic.dart
index d296f62e7cf..c91658d91c1 100644
--- a/benchmarks/Dynamic/dart2/Dynamic.dart
+++ b/benchmarks/Dynamic/dart2/Dynamic.dart
@@ -8,6 +8,8 @@
 // similarly defined functions and closures except that the parameters and
 // return types are all dynamic.
 
+// @dart=2.9
+
 import 'package:benchmark_harness/benchmark_harness.dart';
 
 const int kRepeat = 100;
diff --git a/benchmarks/EventLoopLatencyJson/dart2/EventLoopLatencyJson.dart b/benchmarks/EventLoopLatencyJson/dart2/EventLoopLatencyJson.dart
index 7a8c5ee0e6b..ff187a245c0 100644
--- a/benchmarks/EventLoopLatencyJson/dart2/EventLoopLatencyJson.dart
+++ b/benchmarks/EventLoopLatencyJson/dart2/EventLoopLatencyJson.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:isolate';
 
 import 'json_benchmark.dart';
diff --git a/benchmarks/EventLoopLatencyJson/dart2/json_benchmark.dart b/benchmarks/EventLoopLatencyJson/dart2/json_benchmark.dart
index c29a5b54853..e31c534002b 100644
--- a/benchmarks/EventLoopLatencyJson/dart2/json_benchmark.dart
+++ b/benchmarks/EventLoopLatencyJson/dart2/json_benchmark.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:math';
 import 'dart:convert';
 
diff --git a/benchmarks/EventLoopLatencyJson/dart2/latency.dart b/benchmarks/EventLoopLatencyJson/dart2/latency.dart
index c368802d799..cfec9407f80 100644
--- a/benchmarks/EventLoopLatencyJson/dart2/latency.dart
+++ b/benchmarks/EventLoopLatencyJson/dart2/latency.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:async';
 import 'dart:io';
 import 'dart:math' as math;
diff --git a/benchmarks/Example/dart2/Example.dart b/benchmarks/Example/dart2/Example.dart
index bf0f06fe80d..cd5219e237f 100644
--- a/benchmarks/Example/dart2/Example.dart
+++ b/benchmarks/Example/dart2/Example.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'package:benchmark_harness/benchmark_harness.dart';
 
 class Example extends BenchmarkBase {
diff --git a/benchmarks/FfiBoringssl/dart2/FfiBoringssl.dart b/benchmarks/FfiBoringssl/dart2/FfiBoringssl.dart
index 1e12b3d634a..7db1f91c14f 100644
--- a/benchmarks/FfiBoringssl/dart2/FfiBoringssl.dart
+++ b/benchmarks/FfiBoringssl/dart2/FfiBoringssl.dart
@@ -4,6 +4,8 @@
 
 // Macro-benchmark for ffi with boringssl.
 
+// @dart=2.9
+
 import 'dart:convert';
 import 'dart:ffi';
 import 'dart:typed_data';
diff --git a/benchmarks/FfiBoringssl/dart2/digest.dart b/benchmarks/FfiBoringssl/dart2/digest.dart
index 9af7617a83e..290df60b478 100644
--- a/benchmarks/FfiBoringssl/dart2/digest.dart
+++ b/benchmarks/FfiBoringssl/dart2/digest.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:ffi';
 import 'dart:io';
 
diff --git a/benchmarks/FfiBoringssl/dart2/dlopen_helper.dart b/benchmarks/FfiBoringssl/dart2/dlopen_helper.dart
index 726c181093c..128bff7dd23 100644
--- a/benchmarks/FfiBoringssl/dart2/dlopen_helper.dart
+++ b/benchmarks/FfiBoringssl/dart2/dlopen_helper.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:ffi';
 import 'dart:io';
 
diff --git a/benchmarks/FfiBoringssl/dart2/types.dart b/benchmarks/FfiBoringssl/dart2/types.dart
index 2dd5f76ae42..2c1923ba682 100644
--- a/benchmarks/FfiBoringssl/dart2/types.dart
+++ b/benchmarks/FfiBoringssl/dart2/types.dart
@@ -4,6 +4,8 @@
 
 // ignore_for_file: camel_case_types
 
+// @dart=2.9
+
 import 'dart:ffi';
 
 /// digest algorithm.
diff --git a/benchmarks/FfiCall/dart2/FfiCall.dart b/benchmarks/FfiCall/dart2/FfiCall.dart
index 1c34bc99b7f..fa67dce201c 100644
--- a/benchmarks/FfiCall/dart2/FfiCall.dart
+++ b/benchmarks/FfiCall/dart2/FfiCall.dart
@@ -7,6 +7,8 @@
 // These micro benchmarks track the speed of reading and writing C memory from
 // Dart with a specific marshalling and unmarshalling of data.
 
+// @dart=2.9
+
 import 'dart:ffi';
 import 'dart:io';
 
diff --git a/benchmarks/FfiCall/dart2/dlopen_helper.dart b/benchmarks/FfiCall/dart2/dlopen_helper.dart
index 726c181093c..128bff7dd23 100644
--- a/benchmarks/FfiCall/dart2/dlopen_helper.dart
+++ b/benchmarks/FfiCall/dart2/dlopen_helper.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:ffi';
 import 'dart:io';
 
diff --git a/benchmarks/FfiMemory/dart2/FfiMemory.dart b/benchmarks/FfiMemory/dart2/FfiMemory.dart
index 18a510e836b..11fbea26819 100644
--- a/benchmarks/FfiMemory/dart2/FfiMemory.dart
+++ b/benchmarks/FfiMemory/dart2/FfiMemory.dart
@@ -9,6 +9,8 @@
 // These micro benchmarks track the speed of reading and writing C memory from
 // Dart with a specific marshalling and unmarshalling of data.
 
+// @dart=2.9
+
 import 'dart:ffi';
 
 import 'package:ffi/ffi.dart';
diff --git a/benchmarks/FfiStruct/dart2/FfiStruct.dart b/benchmarks/FfiStruct/dart2/FfiStruct.dart
index 6e7e90d9830..a11e8ab6b3f 100644
--- a/benchmarks/FfiStruct/dart2/FfiStruct.dart
+++ b/benchmarks/FfiStruct/dart2/FfiStruct.dart
@@ -7,6 +7,8 @@
 // Only tests a single field because the FfiMemory benchmark already tests loads
 // and stores of different field sizes.
 
+// @dart=2.9
+
 import 'dart:ffi';
 
 import 'package:ffi/ffi.dart';
diff --git a/benchmarks/Isolate/dart2/Isolate.dart b/benchmarks/Isolate/dart2/Isolate.dart
index aba6224e73a..24e102b038c 100644
--- a/benchmarks/Isolate/dart2/Isolate.dart
+++ b/benchmarks/Isolate/dart2/Isolate.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:async';
 import 'dart:isolate';
 import 'dart:typed_data';
diff --git a/benchmarks/IsolateJson/dart2/IsolateJson.dart b/benchmarks/IsolateJson/dart2/IsolateJson.dart
index 4e64477c5da..46ac6ca3876 100644
--- a/benchmarks/IsolateJson/dart2/IsolateJson.dart
+++ b/benchmarks/IsolateJson/dart2/IsolateJson.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
diff --git a/benchmarks/IsolateSpawn/dart2/IsolateSpawn.dart b/benchmarks/IsolateSpawn/dart2/IsolateSpawn.dart
index a7544415f53..96ebfc422af 100644
--- a/benchmarks/IsolateSpawn/dart2/IsolateSpawn.dart
+++ b/benchmarks/IsolateSpawn/dart2/IsolateSpawn.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:async';
 import 'dart:isolate';
 import 'dart:math';
diff --git a/benchmarks/IsolateSpawn/dart2/helloworld.dart b/benchmarks/IsolateSpawn/dart2/helloworld.dart
index 01af7fa27a1..6b0f19134ab 100644
--- a/benchmarks/IsolateSpawn/dart2/helloworld.dart
+++ b/benchmarks/IsolateSpawn/dart2/helloworld.dart
@@ -1,3 +1,5 @@
+// @dart=2.9
+
 void main() {
   print('Hello, world!');
 }
diff --git a/benchmarks/IsolateSpawnMemory/dart2/IsolateSpawnMemory.dart b/benchmarks/IsolateSpawnMemory/dart2/IsolateSpawnMemory.dart
index 5a13d965ebe..115e705cc35 100644
--- a/benchmarks/IsolateSpawnMemory/dart2/IsolateSpawnMemory.dart
+++ b/benchmarks/IsolateSpawnMemory/dart2/IsolateSpawnMemory.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:async';
 import 'dart:developer';
 import 'dart:io';
diff --git a/benchmarks/IsolateSpawnMemory/dart2/helloworld.dart b/benchmarks/IsolateSpawnMemory/dart2/helloworld.dart
index 01af7fa27a1..6b0f19134ab 100644
--- a/benchmarks/IsolateSpawnMemory/dart2/helloworld.dart
+++ b/benchmarks/IsolateSpawnMemory/dart2/helloworld.dart
@@ -1,3 +1,5 @@
+// @dart=2.9
+
 void main() {
   print('Hello, world!');
 }
diff --git a/benchmarks/ListCopy/dart2/ListCopy.dart b/benchmarks/ListCopy/dart2/ListCopy.dart
index acbb5a165ab..34da1ebcd5a 100644
--- a/benchmarks/ListCopy/dart2/ListCopy.dart
+++ b/benchmarks/ListCopy/dart2/ListCopy.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:collection';
 import 'dart:typed_data';
 import 'package:benchmark_harness/benchmark_harness.dart';
diff --git a/benchmarks/MD5/dart2/md5.dart b/benchmarks/MD5/dart2/md5.dart
index a65803d3233..ab0e2d2e046 100644
--- a/benchmarks/MD5/dart2/md5.dart
+++ b/benchmarks/MD5/dart2/md5.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'package:benchmark_harness/benchmark_harness.dart';
 import 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
diff --git a/benchmarks/RuntimeType/dart2/RuntimeType.dart b/benchmarks/RuntimeType/dart2/RuntimeType.dart
index fe21b30489c..1a7b6d62f6f 100644
--- a/benchmarks/RuntimeType/dart2/RuntimeType.dart
+++ b/benchmarks/RuntimeType/dart2/RuntimeType.dart
@@ -7,6 +7,8 @@
 // ignore_for_file: prefer_const_constructors
 // ignore_for_file: avoid_function_literals_in_foreach_calls
 
+// @dart=2.9
+
 import 'dart:typed_data';
 
 import 'package:benchmark_harness/benchmark_harness.dart';
diff --git a/benchmarks/SHA1/dart2/sha1.dart b/benchmarks/SHA1/dart2/sha1.dart
index 4ce65f5726e..6c5c95af0cc 100644
--- a/benchmarks/SHA1/dart2/sha1.dart
+++ b/benchmarks/SHA1/dart2/sha1.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'package:benchmark_harness/benchmark_harness.dart';
 import 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
diff --git a/benchmarks/SHA256/dart2/sha256.dart b/benchmarks/SHA256/dart2/sha256.dart
index c1383878dff..dd3cae6ec94 100644
--- a/benchmarks/SHA256/dart2/sha256.dart
+++ b/benchmarks/SHA256/dart2/sha256.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'package:benchmark_harness/benchmark_harness.dart';
 import 'package:convert/convert.dart';
 import 'package:crypto/crypto.dart';
diff --git a/benchmarks/SkeletalAnimation/dart2/SkeletalAnimation.dart b/benchmarks/SkeletalAnimation/dart2/SkeletalAnimation.dart
index adda3d3caae..878993c975e 100644
--- a/benchmarks/SkeletalAnimation/dart2/SkeletalAnimation.dart
+++ b/benchmarks/SkeletalAnimation/dart2/SkeletalAnimation.dart
@@ -5,6 +5,8 @@
 /// A Dart implementation of two computation kernels used for skeletal
 /// animation.
 
+// @dart=2.9
+
 import 'dart:typed_data';
 
 import 'package:benchmark_harness/benchmark_harness.dart';
diff --git a/benchmarks/SkeletalAnimationSIMD/dart2/SkeletalAnimationSIMD.dart b/benchmarks/SkeletalAnimationSIMD/dart2/SkeletalAnimationSIMD.dart
index fc7727e99e7..5cf3f4276b8 100644
--- a/benchmarks/SkeletalAnimationSIMD/dart2/SkeletalAnimationSIMD.dart
+++ b/benchmarks/SkeletalAnimationSIMD/dart2/SkeletalAnimationSIMD.dart
@@ -5,6 +5,8 @@
 /// A Dart implementation of two computation kernels used for skeletal
 /// animation. SIMD version.
 
+// @dart=2.9
+
 import 'dart:typed_data';
 
 import 'package:benchmark_harness/benchmark_harness.dart';
diff --git a/benchmarks/SoundSplayTreeSieve/dart2/SoundSplayTreeSieve.dart b/benchmarks/SoundSplayTreeSieve/dart2/SoundSplayTreeSieve.dart
index dfed86c9f45..5c672d416be 100644
--- a/benchmarks/SoundSplayTreeSieve/dart2/SoundSplayTreeSieve.dart
+++ b/benchmarks/SoundSplayTreeSieve/dart2/SoundSplayTreeSieve.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:collection';
 import 'dart:typed_data';
 
diff --git a/benchmarks/SoundSplayTreeSieve/dart2/iterable.dart b/benchmarks/SoundSplayTreeSieve/dart2/iterable.dart
index 6870a3bceb2..3bbdcfa6df9 100644
--- a/benchmarks/SoundSplayTreeSieve/dart2/iterable.dart
+++ b/benchmarks/SoundSplayTreeSieve/dart2/iterable.dart
@@ -1,5 +1,8 @@
 /// Marker interface for [Iterable] subclasses that have an efficient
 /// [length] implementation.
+
+// @dart=2.9
+
 abstract class EfficientLengthIterable<T> extends Iterable<T> {
   const EfficientLengthIterable();
 
diff --git a/benchmarks/SoundSplayTreeSieve/dart2/sound_splay_tree.dart b/benchmarks/SoundSplayTreeSieve/dart2/sound_splay_tree.dart
index dd952f3aa9d..6494a14ad9c 100644
--- a/benchmarks/SoundSplayTreeSieve/dart2/sound_splay_tree.dart
+++ b/benchmarks/SoundSplayTreeSieve/dart2/sound_splay_tree.dart
@@ -2,6 +2,8 @@
 // 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.
 
+// @dart=2.9
+
 import 'dart:collection';
 import 'iterable.dart';
 
diff --git a/benchmarks/TypedDataDuplicate/dart2/TypedDataDuplicate.dart b/benchmarks/TypedDataDuplicate/dart2/TypedDataDuplicate.dart
index d9fb31a0d49..6fc20687888 100644
--- a/benchmarks/TypedDataDuplicate/dart2/TypedDataDuplicate.dart
+++ b/benchmarks/TypedDataDuplicate/dart2/TypedDataDuplicate.dart
@@ -4,6 +4,8 @@
 
 // Micro-benchmarks for copying typed data lists.
 
+// @dart=2.9
+
 import 'dart:typed_data';
 
 import 'package:benchmark_harness/benchmark_harness.dart';
diff --git a/benchmarks/Utf8Decode/dart2/Utf8Decode.dart b/benchmarks/Utf8Decode/dart2/Utf8Decode.dart
index 7be3a8f39f3..03c87edad1f 100644
--- a/benchmarks/Utf8Decode/dart2/Utf8Decode.dart
+++ b/benchmarks/Utf8Decode/dart2/Utf8Decode.dart
@@ -4,6 +4,8 @@
 //
 // Benchmark for UTF-8 decoding
 
+// @dart=2.9
+
 import 'dart:convert';
 import 'dart:typed_data';
 
diff --git a/benchmarks/Utf8Decode/dart2/datext_latin1_10k.dart b/benchmarks/Utf8Decode/dart2/datext_latin1_10k.dart
index bce6c80589b..4e13b7e7f01 100644
--- a/benchmarks/Utf8Decode/dart2/datext_latin1_10k.dart
+++ b/benchmarks/Utf8Decode/dart2/datext_latin1_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String da = '''
 Anders And
 
diff --git a/benchmarks/Utf8Decode/dart2/entext_ascii_10k.dart b/benchmarks/Utf8Decode/dart2/entext_ascii_10k.dart
index 82cb7218946..d7da461074d 100644
--- a/benchmarks/Utf8Decode/dart2/entext_ascii_10k.dart
+++ b/benchmarks/Utf8Decode/dart2/entext_ascii_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String en = '''
 Anarchism
 
diff --git a/benchmarks/Utf8Decode/dart2/netext_3_10k.dart b/benchmarks/Utf8Decode/dart2/netext_3_10k.dart
index 8fce5509349..1538945d06f 100644
--- a/benchmarks/Utf8Decode/dart2/netext_3_10k.dart
+++ b/benchmarks/Utf8Decode/dart2/netext_3_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String ne = '''
 नेपाल
 
diff --git a/benchmarks/Utf8Decode/dart2/rutext_2_10k.dart b/benchmarks/Utf8Decode/dart2/rutext_2_10k.dart
index c61a665739c..55295d7b487 100644
--- a/benchmarks/Utf8Decode/dart2/rutext_2_10k.dart
+++ b/benchmarks/Utf8Decode/dart2/rutext_2_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String ru = '''
 Литва
 
diff --git a/benchmarks/Utf8Decode/dart2/sktext_10k.dart b/benchmarks/Utf8Decode/dart2/sktext_10k.dart
index 7dc2d133ec6..198c2743858 100644
--- a/benchmarks/Utf8Decode/dart2/sktext_10k.dart
+++ b/benchmarks/Utf8Decode/dart2/sktext_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String sk = '''
 Esperanto (pôvodne Lingvo Internacia – „medzinárodný jazyk“) je najrozšírenejší medzinárodný plánový jazyk. Názov je odvodený od pseudonymu, pod ktorým v roku 1887 zverejnil lekár L. L. Zamenhof základy tohto jazyka. Zámerom tvorcu bolo vytvoriť ľahko naučiteľný a použiteľný neutrálny jazyk, vhodný na použitie v medzinárodnej komunikácii. Cieľom nebolo nahradiť národné jazyky, čo bolo neskôr aj deklarované v Boulonskej deklarácii.
 
diff --git a/benchmarks/Utf8Decode/dart2/zhtext_10k.dart b/benchmarks/Utf8Decode/dart2/zhtext_10k.dart
index b5e2a541298..20e50d9c912 100644
--- a/benchmarks/Utf8Decode/dart2/zhtext_10k.dart
+++ b/benchmarks/Utf8Decode/dart2/zhtext_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String zh = '''
 最簡單的漢字只有一笔画，但卻不止一個字：除了「一」字以外，「乙」、「〇」、「丶」、「丨」、「亅」、「丿」、「乀」、「乁」、「𠄌」、「𠃋」、「𠃉」、「𠃊」、「乚」等都是漢字，而且都有各自的讀音。
 
diff --git a/benchmarks/Utf8Encode/dart2/Utf8Encode.dart b/benchmarks/Utf8Encode/dart2/Utf8Encode.dart
index 71ca4c9bc90..1d6e35ac042 100644
--- a/benchmarks/Utf8Encode/dart2/Utf8Encode.dart
+++ b/benchmarks/Utf8Encode/dart2/Utf8Encode.dart
@@ -4,6 +4,8 @@
 //
 // Benchmark for UTF-8 encoding
 
+// @dart=2.9
+
 import 'dart:convert';
 
 import 'package:benchmark_harness/benchmark_harness.dart';
diff --git a/benchmarks/Utf8Encode/dart2/datext_latin1_10k.dart b/benchmarks/Utf8Encode/dart2/datext_latin1_10k.dart
index bce6c80589b..4e13b7e7f01 100644
--- a/benchmarks/Utf8Encode/dart2/datext_latin1_10k.dart
+++ b/benchmarks/Utf8Encode/dart2/datext_latin1_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String da = '''
 Anders And
 
diff --git a/benchmarks/Utf8Encode/dart2/entext_ascii_10k.dart b/benchmarks/Utf8Encode/dart2/entext_ascii_10k.dart
index 82cb7218946..d7da461074d 100644
--- a/benchmarks/Utf8Encode/dart2/entext_ascii_10k.dart
+++ b/benchmarks/Utf8Encode/dart2/entext_ascii_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String en = '''
 Anarchism
 
diff --git a/benchmarks/Utf8Encode/dart2/netext_3_10k.dart b/benchmarks/Utf8Encode/dart2/netext_3_10k.dart
index 8fce5509349..1538945d06f 100644
--- a/benchmarks/Utf8Encode/dart2/netext_3_10k.dart
+++ b/benchmarks/Utf8Encode/dart2/netext_3_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String ne = '''
 नेपाल
 
diff --git a/benchmarks/Utf8Encode/dart2/rutext_2_10k.dart b/benchmarks/Utf8Encode/dart2/rutext_2_10k.dart
index c61a665739c..55295d7b487 100644
--- a/benchmarks/Utf8Encode/dart2/rutext_2_10k.dart
+++ b/benchmarks/Utf8Encode/dart2/rutext_2_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String ru = '''
 Литва
 
diff --git a/benchmarks/Utf8Encode/dart2/sktext_10k.dart b/benchmarks/Utf8Encode/dart2/sktext_10k.dart
index 7dc2d133ec6..198c2743858 100644
--- a/benchmarks/Utf8Encode/dart2/sktext_10k.dart
+++ b/benchmarks/Utf8Encode/dart2/sktext_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String sk = '''
 Esperanto (pôvodne Lingvo Internacia – „medzinárodný jazyk“) je najrozšírenejší medzinárodný plánový jazyk. Názov je odvodený od pseudonymu, pod ktorým v roku 1887 zverejnil lekár L. L. Zamenhof základy tohto jazyka. Zámerom tvorcu bolo vytvoriť ľahko naučiteľný a použiteľný neutrálny jazyk, vhodný na použitie v medzinárodnej komunikácii. Cieľom nebolo nahradiť národné jazyky, čo bolo neskôr aj deklarované v Boulonskej deklarácii.
 
diff --git a/benchmarks/Utf8Encode/dart2/zhtext_10k.dart b/benchmarks/Utf8Encode/dart2/zhtext_10k.dart
index b5e2a541298..20e50d9c912 100644
--- a/benchmarks/Utf8Encode/dart2/zhtext_10k.dart
+++ b/benchmarks/Utf8Encode/dart2/zhtext_10k.dart
@@ -7,6 +7,8 @@
 // The material is licensed under the Creative Commons Attribution-Share-Alike
 // License 3.0: https://creativecommons.org/licenses/by-sa/3.0/
 
+// @dart=2.9
+
 const String zh = '''
 最簡單的漢字只有一笔画，但卻不止一個字：除了「一」字以外，「乙」、「〇」、「丶」、「丨」、「亅」、「丿」、「乀」、「乁」、「𠄌」、「𠃋」、「𠃉」、「𠃊」、「乚」等都是漢字，而且都有各自的讀音。