diff --git a/webdev/CHANGELOG.md b/webdev/CHANGELOG.md
index 47a6f1ef7..940081862 100644
--- a/webdev/CHANGELOG.md
+++ b/webdev/CHANGELOG.md
@@ -1,4 +1,5 @@
-## 3.8.0-wip
+## 4.0.0-wip
+ - Remove deprecated `--null-safety` flag. Dart 3 only supports [sound null safety](https://dart.dev/null-safety).
 
 ## 3.7.2
 
diff --git a/webdev/lib/src/command/configuration.dart b/webdev/lib/src/command/configuration.dart
index 07f532261..3ee9cb277 100644
--- a/webdev/lib/src/command/configuration.dart
+++ b/webdev/lib/src/command/configuration.dart
@@ -30,10 +30,6 @@ const releaseFlag = 'release';
 const requireBuildWebCompilersFlag = 'build-web-compilers';
 const enableExpressionEvaluationFlag = 'enable-expression-evaluation';
 const verboseFlag = 'verbose';
-const nullSafetyFlag = 'null-safety';
-const nullSafetySound = 'sound';
-const nullSafetyUnsound = 'unsound';
-const nullSafetyAuto = 'auto';
 const disableDdsFlag = 'disable-dds';
 const enableExperimentOption = 'enable-experiment';
 const canaryFeaturesFlag = 'canary';
@@ -105,7 +101,6 @@ class Configuration {
   final bool? _enableExpressionEvaluation;
   final bool? _verbose;
   final bool? _disableDds;
-  final String? _nullSafety;
   final List<String>? _experiments;
   final bool? _canaryFeatures;
   final bool? _offline;
@@ -132,7 +127,6 @@ class Configuration {
     bool? enableExpressionEvaluation,
     bool? verbose,
     bool? disableDds,
-    String? nullSafety,
     List<String>? experiments,
     bool? canaryFeatures,
     bool? offline,
@@ -155,7 +149,6 @@ class Configuration {
         _disableDds = disableDds,
         _enableExpressionEvaluation = enableExpressionEvaluation,
         _verbose = verbose,
-        _nullSafety = nullSafety,
         _experiments = experiments,
         _canaryFeatures = canaryFeatures,
         _offline = offline {
@@ -231,7 +224,6 @@ class Configuration {
       enableExpressionEvaluation:
           other._enableExpressionEvaluation ?? _enableExpressionEvaluation,
       verbose: other._verbose ?? _verbose,
-      nullSafety: other._nullSafety ?? _nullSafety,
       experiments: other._experiments ?? _experiments,
       canaryFeatures: other._canaryFeatures ?? _canaryFeatures,
       offline: other._offline ?? _offline);
@@ -278,13 +270,6 @@ class Configuration {
 
   bool get verbose => _verbose ?? false;
 
-  /// Null safety mode:
-  ///
-  /// 'sound', 'unsound', or 'auto'.
-  /// 'auto' indicates that the default `package:build_web_compilers`
-  /// behavior should be used.
-  String get nullSafety => _nullSafety ?? 'auto';
-
   List<String> get experiments => _experiments ?? [];
 
   bool get canaryFeatures => _canaryFeatures ?? false;
@@ -398,10 +383,6 @@ class Configuration {
         ? argResults[verboseFlag] as bool?
         : defaultConfiguration.verbose;
 
-    final nullSafety = argResults.options.contains(nullSafetyFlag)
-        ? argResults[nullSafetyFlag] as String?
-        : defaultConfiguration.nullSafety;
-
     final disableDds = argResults.options.contains(disableDdsFlag)
         ? argResults[disableDdsFlag] as bool?
         : defaultConfiguration.disableDds;
@@ -441,7 +422,6 @@ class Configuration {
       disableDds: disableDds,
       enableExpressionEvaluation: enableExpressionEvaluation,
       verbose: verbose,
-      nullSafety: nullSafety,
       experiments: experiments,
       canaryFeatures: canaryFeatures,
       offline: offline,
diff --git a/webdev/lib/src/command/shared.dart b/webdev/lib/src/command/shared.dart
index 097a893c9..308c89e5e 100644
--- a/webdev/lib/src/command/shared.dart
+++ b/webdev/lib/src/command/shared.dart
@@ -28,18 +28,6 @@ void addSharedArgs(ArgParser argParser,
           'A value of "NONE" indicates that no "--output" value should be '
           'passed to `build_runner`.',
     )
-    ..addOption(nullSafetyFlag,
-        abbr: 'n',
-        defaultsTo: nullSafetyAuto,
-        allowed: [nullSafetySound, nullSafetyUnsound, nullSafetyAuto],
-        help:
-            'DEPRECATED: If "sound", `package:build_web_compilers` will be run '
-            'with sound null safety support. '
-            'If "unsound", `package:build_web_compilers` will be run without '
-            'sound null safety support. '
-            'If "auto", the default `package:build_web_compilers` '
-            'behavior is used.',
-        hide: true)
     ..addFlag(releaseFlag,
         abbr: 'r',
         defaultsTo: releaseDefault,
diff --git a/webdev/test/configuration_test.dart b/webdev/test/configuration_test.dart
index 5fccfd2d0..9d9fa766b 100644
--- a/webdev/test/configuration_test.dart
+++ b/webdev/test/configuration_test.dart
@@ -12,7 +12,6 @@ void main() {
     argParser = ArgParser()
       ..addFlag('release')
       ..addFlag(launchInChromeFlag, defaultsTo: false)
-      ..addOption(nullSafetyFlag, defaultsTo: nullSafetyAuto)
       ..addOption(userDataDirFlag, defaultsTo: null);
   });
 
@@ -71,12 +70,6 @@ void main() {
         throwsA(isA<InvalidConfiguration>()));
   });
 
-  test('nullSafety defaults to auto', () {
-    final argResults = argParser.parse(['']);
-    final defaultConfiguration = Configuration.fromArgs(argResults);
-    expect(defaultConfiguration.nullSafety, equals(nullSafetyAuto));
-  });
-
   test(
       'must not provide debug related configuration when enableInjectedClient '
       'is false', () {
diff --git a/webdev/test/e2e_test.dart b/webdev/test/e2e_test.dart
index 87c07f74d..c438440b4 100644
--- a/webdev/test/e2e_test.dart
+++ b/webdev/test/e2e_test.dart
@@ -153,30 +153,6 @@ void main() {
         skip: Platform.isWindows,
       );
     }
-    test(
-      'and --null-safety=sound',
-      () async {
-        final args = [
-          'build',
-          '-o',
-          'web:${d.sandbox}',
-          '--no-release',
-          '--null-safety=sound'
-        ];
-
-        final process = await testRunner.runWebDev(args,
-            workingDirectory: soundExampleDirectory);
-
-        final expectedItems = <Object>['Built with build_runner'];
-
-        await checkProcessStdout(process, expectedItems);
-        await process.shouldExit(0);
-
-        await d.file('main.ddc.js', isNotEmpty).validate();
-      },
-      // https://github.com/dart-lang/webdev/issues/2489
-      skip: Platform.isWindows,
-    );
   });
 
   group('should build with --output=NONE', () {
@@ -281,7 +257,6 @@ void main() {
           'daemon',
           'web:$openPort',
           '--enable-expression-evaluation',
-          '--null-safety=sound',
           '--verbose',
         ];
         final process = await testRunner.runWebDev(args,