diff --git a/pkg/compiler/test/end_to_end/dill_loader_test.dart b/pkg/compiler/test/end_to_end/dill_loader_test.dart
index fe24e883fb8..8cfe81aee43 100644
--- a/pkg/compiler/test/end_to_end/dill_loader_test.dart
+++ b/pkg/compiler/test/end_to_end/dill_loader_test.dart
@@ -28,7 +28,7 @@ main() {
     var options = CompilerOptions()
       ..target = Dart2jsTarget("dart2js", TargetFlags(enableNullSafety: true))
       ..nnbdMode = NnbdMode.Strong
-      ..packagesFileUri = Uri.base.resolve('.packages')
+      ..packagesFileUri = Uri.base.resolve('.dart_tool/package_config.json')
       ..additionalDills = <Uri>[
         computePlatformBinariesLocation().resolve("dart2js_platform.dill"),
       ]
diff --git a/pkg/compiler/test/end_to_end/no_platform_test.dart b/pkg/compiler/test/end_to_end/no_platform_test.dart
index e786f3f8cc3..349b129e37e 100644
--- a/pkg/compiler/test/end_to_end/no_platform_test.dart
+++ b/pkg/compiler/test/end_to_end/no_platform_test.dart
@@ -22,7 +22,8 @@ main() {
             new Dart2jsTarget('dart2js', new TargetFlags()),
             sdkLibrariesSpecificationUri,
             [], // additionalDills
-            Uri.base.resolve('.packages'), // packagesFileUri
+            Uri.base
+                .resolve('.dart_tool/package_config.json'), // packagesFileUri
             explicitExperimentalFlags: experimentalFlags,
             verify: true);
     ir.Component component = await fe.compile(
diff --git a/pkg/compiler/test/helpers/memory_compiler.dart b/pkg/compiler/test/helpers/memory_compiler.dart
index 04ec18ce269..310120af8cf 100644
--- a/pkg/compiler/test/helpers/memory_compiler.dart
+++ b/pkg/compiler/test/helpers/memory_compiler.dart
@@ -133,8 +133,8 @@ Compiler compilerFor(
       packageConfig = Uri.base.resolve(Platform.packageConfig);
     } else {
       // The tests are run with the base directory as the SDK root
-      // so just use the .packages file there.
-      packageConfig = Uri.base.resolve('.packages');
+      // so just use the package config there.
+      packageConfig = Uri.base.resolve('.dart_tool/package_config.json');
     }
   }
 
diff --git a/pkg/dev_compiler/test/sourcemap/sourcemaps_ddk_suite.dart b/pkg/dev_compiler/test/sourcemap/sourcemaps_ddk_suite.dart
index ea96e196e7d..e75d3d00e41 100644
--- a/pkg/dev_compiler/test/sourcemap/sourcemaps_ddk_suite.dart
+++ b/pkg/dev_compiler/test/sourcemap/sourcemaps_ddk_suite.dart
@@ -59,8 +59,10 @@ class DevCompilerRunner implements CompilerRunner {
 
     var ddcSdkSummary = findInOutDir('ddc_outline.dill');
 
+    var packageConfigPath =
+        sdkRoot.uri.resolve('.dart_tool/package_config.json').toFilePath();
     var args = <String>[
-      "--packages=${sdkRoot.uri.resolve(".packages").toFilePath()}",
+      '--packages=$packageConfigPath',
       '--modules=es6',
       '--dart-sdk-summary=${ddcSdkSummary.path}',
       '-o',
diff --git a/pkg/front_end/test/async_but_no_await_git_test.dart b/pkg/front_end/test/async_but_no_await_git_test.dart
index 6721ee120f2..fb27bc24d74 100644
--- a/pkg/front_end/test/async_but_no_await_git_test.dart
+++ b/pkg/front_end/test/async_but_no_await_git_test.dart
@@ -31,11 +31,11 @@ Set<Uri> libUris = {};
 Future<void> main(List<String> args) async {
   api.CompilerOptions compilerOptions = getOptions();
 
-  Uri dotPackagesUri = repoDir.resolve(".packages");
-  if (!new File.fromUri(dotPackagesUri).existsSync()) {
+  Uri packageConfigUri = repoDir.resolve(".dart_tool/package_config.json");
+  if (!new File.fromUri(packageConfigUri).existsSync()) {
     throw "Couldn't find .packages";
   }
-  compilerOptions.packagesFileUri = dotPackagesUri;
+  compilerOptions.packagesFileUri = packageConfigUri;
 
   ProcessedOptions options = new ProcessedOptions(options: compilerOptions);
 
diff --git a/pkg/front_end/test/comments_on_certain_arguments_tool.dart b/pkg/front_end/test/comments_on_certain_arguments_tool.dart
index 3607cc250d9..c588afcf187 100644
--- a/pkg/front_end/test/comments_on_certain_arguments_tool.dart
+++ b/pkg/front_end/test/comments_on_certain_arguments_tool.dart
@@ -61,11 +61,11 @@ late Component component;
 Future<void> main(List<String> args) async {
   api.CompilerOptions compilerOptions = getOptions();
 
-  Uri dotPackagesUri = repoDir.resolve(".packages");
-  if (!new File.fromUri(dotPackagesUri).existsSync()) {
-    throw "Couldn't find .packages";
+  Uri packageConfigUri = repoDir.resolve(".dart_tool/package_config.json");
+  if (!new File.fromUri(packageConfigUri).existsSync()) {
+    throw "Couldn't find .dart_tool/package_config.json";
   }
-  compilerOptions.packagesFileUri = dotPackagesUri;
+  compilerOptions.packagesFileUri = packageConfigUri;
 
   ProcessedOptions options = new ProcessedOptions(options: compilerOptions);
 
diff --git a/pkg/front_end/test/deps_git_test.dart b/pkg/front_end/test/deps_git_test.dart
index 201735214aa..e123def944f 100644
--- a/pkg/front_end/test/deps_git_test.dart
+++ b/pkg/front_end/test/deps_git_test.dart
@@ -49,11 +49,11 @@ Future<void> main() async {
   Ticker ticker = new Ticker(isVerbose: false);
   CompilerOptions compilerOptions = getOptions();
 
-  Uri dotPackagesUri = repoDir.resolve(".packages");
-  if (!new File.fromUri(dotPackagesUri).existsSync()) {
-    throw "Couldn't find .packages";
+  Uri packageConfigUri = repoDir.resolve(".dart_tool/package_config.json");
+  if (!new File.fromUri(packageConfigUri).existsSync()) {
+    throw "Couldn't find .dart_tool/package_config.json";
   }
-  compilerOptions.packagesFileUri = dotPackagesUri;
+  compilerOptions.packagesFileUri = packageConfigUri;
 
   ProcessedOptions options = new ProcessedOptions(options: compilerOptions);
 
@@ -123,7 +123,7 @@ Future<void> main() async {
   // * Everything else is an error.
 
   // Remove white-listed non-dart files.
-  otherNonDartUris.remove(dotPackagesUri);
+  otherNonDartUris.remove(packageConfigUri);
   otherNonDartUris.remove(repoDir.resolve("sdk/lib/libraries.json"));
   otherNonDartUris.remove(repoDir.resolve(".dart_tool/package_config.json"));
 
diff --git a/pkg/front_end/test/explicit_creation_git_test.dart b/pkg/front_end/test/explicit_creation_git_test.dart
index 3200635d4c1..9a6676c254a 100644
--- a/pkg/front_end/test/explicit_creation_git_test.dart
+++ b/pkg/front_end/test/explicit_creation_git_test.dart
@@ -49,11 +49,11 @@ Future<void> main(List<String> args) async {
   Ticker ticker = new Ticker(isVerbose: false);
   api.CompilerOptions compilerOptions = getOptions();
 
-  Uri dotPackagesUri = repoDir.resolve(".packages");
-  if (!new File.fromUri(dotPackagesUri).existsSync()) {
-    throw "Couldn't find .packages";
+  Uri packageConfigUri = repoDir.resolve(".dart_tool/package_config.json");
+  if (!new File.fromUri(packageConfigUri).existsSync()) {
+    throw "Couldn't find .dart_tool/package_config.json";
   }
-  compilerOptions.packagesFileUri = dotPackagesUri;
+  compilerOptions.packagesFileUri = packageConfigUri;
 
   ProcessedOptions options = new ProcessedOptions(options: compilerOptions);
 
diff --git a/pkg/front_end/test/fasta/incremental_hello_test.dart b/pkg/front_end/test/fasta/incremental_hello_test.dart
index 125ef123406..6a6daac4b3a 100644
--- a/pkg/front_end/test/fasta/incremental_hello_test.dart
+++ b/pkg/front_end/test/fasta/incremental_hello_test.dart
@@ -37,7 +37,7 @@ void diagnosticMessageHandler(DiagnosticMessage message) {
 
 Future<void> test({required bool sdkFromSource}) async {
   final CompilerOptions optionBuilder = new CompilerOptions()
-    ..packagesFileUri = Uri.base.resolve(".packages")
+    ..packagesFileUri = Uri.base.resolve(".dart_tool/package_config.json")
     ..target = new VmTarget(new TargetFlags())
     ..omitPlatform = true
     ..onDiagnostic = diagnosticMessageHandler
diff --git a/pkg/front_end/test/fasta/testing/suite.dart b/pkg/front_end/test/fasta/testing/suite.dart
index 65269ddfeda..bbbcbc6bc8b 100644
--- a/pkg/front_end/test/fasta/testing/suite.dart
+++ b/pkg/front_end/test/fasta/testing/suite.dart
@@ -537,7 +537,7 @@ class FastaContext extends ChainContext with MatchContext {
     UriTranslator? uriTranslator = _uriTranslators[uriConfiguration];
     if (uriTranslator == null) {
       Uri sdk = Uri.base.resolve("sdk/");
-      Uri packages = Uri.base.resolve(".packages");
+      Uri packages = Uri.base.resolve(".dart_tool/package_config.json");
       FolderOptions folderOptions = computeFolderOptions(description);
       CompilerOptions compilerOptions = new CompilerOptions()
         ..onDiagnostic = (DiagnosticMessage message) {
diff --git a/pkg/front_end/test/fasta/types/dill_hierarchy_test.dart b/pkg/front_end/test/fasta/types/dill_hierarchy_test.dart
index a1c2094c847..193d73477ad 100644
--- a/pkg/front_end/test/fasta/types/dill_hierarchy_test.dart
+++ b/pkg/front_end/test/fasta/types/dill_hierarchy_test.dart
@@ -86,7 +86,8 @@ class F implements D<int, bool>;""",
 
   final CompilerContext context = new CompilerContext(new ProcessedOptions(
       options: new CompilerOptions()
-        ..packagesFileUri = Uri.base.resolve(".packages")));
+        ..packagesFileUri =
+            Uri.base.resolve(".dart_tool/package_config.json")));
 
   asyncTest(() => context.runInContext<void>((_) async {
         DillTarget target = new DillTarget(
diff --git a/pkg/front_end/test/fasta/types/fasta_legacy_upper_bound_test.dart b/pkg/front_end/test/fasta/types/fasta_legacy_upper_bound_test.dart
index 618c014f589..e4466af4002 100644
--- a/pkg/front_end/test/fasta/types/fasta_legacy_upper_bound_test.dart
+++ b/pkg/front_end/test/fasta/types/fasta_legacy_upper_bound_test.dart
@@ -66,7 +66,8 @@ void main() {
   final Ticker ticker = new Ticker();
   final CompilerContext context = new CompilerContext(new ProcessedOptions(
       options: new CompilerOptions()
-        ..packagesFileUri = Uri.base.resolve(".packages")));
+        ..packagesFileUri =
+            Uri.base.resolve(".dart_tool/package_config.json")));
   context.runInContext<void>(
       (_) => new FastaLegacyUpperBoundTest(ticker, context).test());
 }
diff --git a/pkg/front_end/test/fasta/types/fasta_types_test.dart b/pkg/front_end/test/fasta/types/fasta_types_test.dart
index 55095c733a2..efbfacc160d 100644
--- a/pkg/front_end/test/fasta/types/fasta_types_test.dart
+++ b/pkg/front_end/test/fasta/types/fasta_types_test.dart
@@ -42,7 +42,8 @@ void main() {
   final Ticker ticker = new Ticker(isVerbose: false);
   final CompilerContext context = new CompilerContext(new ProcessedOptions(
       options: new CompilerOptions()
-        ..packagesFileUri = Uri.base.resolve(".packages")));
+        ..packagesFileUri =
+            Uri.base.resolve(".dart_tool/package_config.json")));
   final Uri uri = Uri.parse("dart:core");
   final TypeParserEnvironment environment = new TypeParserEnvironment(uri, uri);
   final Component sdk = parseSdk(uri, environment);
diff --git a/pkg/front_end/test/fasta/types/subtypes_benchmark.dart b/pkg/front_end/test/fasta/types/subtypes_benchmark.dart
index 165313e03a1..d1f142842d1 100644
--- a/pkg/front_end/test/fasta/types/subtypes_benchmark.dart
+++ b/pkg/front_end/test/fasta/types/subtypes_benchmark.dart
@@ -138,7 +138,8 @@ Future<void> run(Uri benchmarkInput, String name) async {
 
   final CompilerContext context = new CompilerContext(new ProcessedOptions(
       options: new CompilerOptions()
-        ..packagesFileUri = Uri.base.resolve(".packages")));
+        ..packagesFileUri =
+            Uri.base.resolve(".dart_tool/package_config.json")));
   await context.runInContext<void>((_) async {
     DillTarget target = new DillTarget(
         ticker,
diff --git a/pkg/front_end/test/outline_extractor_suite.dart b/pkg/front_end/test/outline_extractor_suite.dart
index 80754c77842..02be7f579f9 100644
--- a/pkg/front_end/test/outline_extractor_suite.dart
+++ b/pkg/front_end/test/outline_extractor_suite.dart
@@ -100,7 +100,7 @@ class OutlineExtractorStep
   @override
   Future<Result<TestDescription>> run(
       TestDescription description, Context context) async {
-    Uri? packages = description.uri.resolve(".packages");
+    Uri? packages = description.uri.resolve(".dart_tool/package_config.json");
     if (!new File.fromUri(packages).existsSync()) {
       packages = null;
     }
@@ -142,7 +142,7 @@ class CompileAndCompareStep
   @override
   Future<Result<TestDescription>> run(
       TestDescription description, Context context) async {
-    Uri? packages = description.uri.resolve(".packages");
+    Uri? packages = description.uri.resolve(".dart_tool/package_config.json");
     if (!new File.fromUri(packages).existsSync()) {
       packages = null;
     }
diff --git a/pkg/front_end/test/outline_extractor_tester.dart b/pkg/front_end/test/outline_extractor_tester.dart
index 941b5c08d42..01fbca9ccf6 100644
--- a/pkg/front_end/test/outline_extractor_tester.dart
+++ b/pkg/front_end/test/outline_extractor_tester.dart
@@ -18,7 +18,7 @@ import 'package:package_config/package_config.dart';
 Future<void> main(List<String> args) async {
   if (args.length != 1) throw "Wants 1 argument.";
   Uri input = Uri.base.resolve(args.single);
-  Uri packageUri = input.resolve(".packages");
+  Uri packageUri = input.resolve(".dart_tool/package_config.json");
   Stopwatch stopwatch = new Stopwatch()..start();
   PackageConfig packageFile = await loadPackageConfigUri(packageUri);
   print("Read packages file in ${stopwatch.elapsedMilliseconds} ms");
diff --git a/pkg/front_end/test/packages_format_error_test.dart b/pkg/front_end/test/packages_format_error_test.dart
index a19551ff6c0..593e1bd3a03 100644
--- a/pkg/front_end/test/packages_format_error_test.dart
+++ b/pkg/front_end/test/packages_format_error_test.dart
@@ -26,7 +26,7 @@ import 'package:front_end/src/fasta/messages.dart'
 void main() {
   Uri root = Uri.parse("org-dartlang-test:///");
   MemoryFileSystem fs = new MemoryFileSystem(root);
-  Uri packages = root.resolve(".packages");
+  Uri packages = root.resolve(".dart_tool/package_config.json");
   fs.entityForUri(packages).writeAsStringSync("bad\n");
   List<DiagnosticMessage> messages = <DiagnosticMessage>[];
   CompilerContext c = new CompilerContext(new ProcessedOptions(
diff --git a/pkg/front_end/test/parts/parts_test.dart b/pkg/front_end/test/parts/parts_test.dart
index 9bfe8fff72c..3e42c006869 100644
--- a/pkg/front_end/test/parts/parts_test.dart
+++ b/pkg/front_end/test/parts/parts_test.dart
@@ -13,7 +13,7 @@ Future<void> main() async {
   Directory dataDir = new Directory.fromUri(Platform.script.resolve('data'));
   CompilerOptions options = new CompilerOptions()
     ..sdkRoot = computePlatformBinariesLocation()
-    ..packagesFileUri = Uri.base.resolve('.packages');
+    ..packagesFileUri = Uri.base.resolve('.dart_tool/package_config.json');
   for (FileSystemEntity dir in dataDir.listSync()) {
     if (dir is Directory) {
       print('Compiling ${dir.path}');
diff --git a/pkg/testing/lib/src/discover.dart b/pkg/testing/lib/src/discover.dart
index 6b761abb90f..193590b76a6 100644
--- a/pkg/testing/lib/src/discover.dart
+++ b/pkg/testing/lib/src/discover.dart
@@ -62,7 +62,7 @@ Stream<FileBasedTestDescription> listTests(List<Uri> testRoots,
 Uri computePackageConfig() {
   String? path = Platform.packageConfig;
   if (path != null) return Uri.base.resolve(path);
-  return Uri.base.resolve(".packages");
+  return Uri.base.resolve(".dart_tool/package_config.json");
 }
 
 // TODO(eernst): Use `bool.hasEnvironment` below when possible;