diff --git a/DEPS b/DEPS
index e2ed777..dc0dbdd 100644
--- a/DEPS
+++ b/DEPS
@@ -44,7 +44,7 @@
   # co19 is a cipd package. Use update.sh in tests/co19[_2] to update these
   # hashes. It requires access to the dart-build-access group, which EngProd
   # has.
-  "co19_rev": "cc4df792d0f02f15bfe04911c1f856b90cb7cbf4",
+  "co19_rev": "a3af05fb4ee10b065bf0f5bfe4e9546bc077d5e8",
   "co19_2_rev": "7637bcb24abf21b5e2f8dd24d3fe619f777391f5",
 
   # The internal benchmarks to use. See go/dart-benchmarks-internal
diff --git a/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart b/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart
index 4d5f23b..4cd2f61f 100644
--- a/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart
+++ b/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart
@@ -2223,18 +2223,6 @@
 }
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
-const Code<Null> codeDeprecateDartExt = messageDeprecateDartExt;
-
-// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
-const MessageCode messageDeprecateDartExt = const MessageCode(
-    "DeprecateDartExt",
-    severity: Severity.info,
-    message:
-        r"""Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK.""",
-    tip:
-        r"""Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)""");
-
-// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Template<
         Message Function(
             int count, int count2, num _num1, num _num2, num _num3)>
@@ -9937,6 +9925,16 @@
 }
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeUnsupportedDartExt = messageUnsupportedDartExt;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageUnsupportedDartExt = const MessageCode(
+    "UnsupportedDartExt",
+    message: r"""Dart native extensions are no longer supported.""",
+    tip:
+        r"""Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)""");
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Template<Message Function(Token token)> templateUnsupportedOperator =
     const Template<Message Function(Token token)>(
         messageTemplate: r"""The '#lexeme' operator is not supported.""",
diff --git a/pkg/front_end/lib/src/fasta/source/source_library_builder.dart b/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
index cfe588b..3cf100e 100644
--- a/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
@@ -715,7 +715,7 @@
     String? nativePath;
     const String nativeExtensionScheme = "dart-ext:";
     if (uri.startsWith(nativeExtensionScheme)) {
-      addProblem(messageDeprecateDartExt, charOffset, noLength, fileUri);
+      addProblem(messageUnsupportedDartExt, charOffset, noLength, fileUri);
       String strippedUri = uri.substring(nativeExtensionScheme.length);
       if (strippedUri.startsWith("package")) {
         resolvedUri = resolve(this.importUri, strippedUri,
diff --git a/pkg/front_end/messages.status b/pkg/front_end/messages.status
index 7348fe6..9feaf38 100644
--- a/pkg/front_end/messages.status
+++ b/pkg/front_end/messages.status
@@ -184,8 +184,6 @@
 DeferredExtensionImport/part_wrapped_script: Fail
 DeferredPrefixDuplicated/example: Fail
 DeferredTypeAnnotation/example: Fail
-DeprecateDartExt/analyzerCode: Fail
-DeprecateDartExt/part_wrapped_script: Fail # Example uses import declaration.
 DillOutlineSummary/analyzerCode: Fail
 DillOutlineSummary/example: Fail
 DirectiveAfterDeclaration/part_wrapped_script1: Fail
@@ -823,6 +821,8 @@
 UnmatchedToken/script3: Fail
 Unspecified/analyzerCode: Fail
 Unspecified/example: Fail
+UnsupportedDartExt/analyzerCode: Fail
+UnsupportedDartExt/part_wrapped_script: Fail # Example uses import declaration.
 UnterminatedString/part_wrapped_script2: Fail
 UnterminatedString/part_wrapped_script4: Fail
 UnterminatedString/part_wrapped_script5: Fail
diff --git a/pkg/front_end/messages.yaml b/pkg/front_end/messages.yaml
index 8e4c7f0..043ae81 100644
--- a/pkg/front_end/messages.yaml
+++ b/pkg/front_end/messages.yaml
@@ -5232,10 +5232,9 @@
     // @dart=2.9
     main() {}
 
-DeprecateDartExt:
-  template: "Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK."
+UnsupportedDartExt:
+  template: "Dart native extensions are no longer supported."
   tip: "Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)"
-  severity: INFO
   script: |
     import 'dart-ext:foo.dart';
 
diff --git a/pkg/front_end/testcases/general/external_import.dart.weak.expect b/pkg/front_end/testcases/general/external_import.dart.weak.expect
index b4adba8..0d7662f 100644
--- a/pkg/front_end/testcases/general/external_import.dart.weak.expect
+++ b/pkg/front_end/testcases/general/external_import.dart.weak.expect
@@ -5,17 +5,17 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/general/external_import.dart:7:1: Info: Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK.
+// pkg/front_end/testcases/general/external_import.dart:7:1: Error: Dart native extensions are no longer supported.
 // Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)
 // import 'dart-ext:here';
 // ^
 //
-// pkg/front_end/testcases/general/external_import.dart:8:1: Info: Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK.
+// pkg/front_end/testcases/general/external_import.dart:8:1: Error: Dart native extensions are no longer supported.
 // Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)
 // import 'dart-ext:foo/../there';
 // ^
 //
-// pkg/front_end/testcases/general/external_import.dart:9:1: Info: Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK.
+// pkg/front_end/testcases/general/external_import.dart:9:1: Error: Dart native extensions are no longer supported.
 // Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)
 // import 'dart-ext:/usr/local/somewhere';
 // ^
diff --git a/pkg/front_end/testcases/general/external_import.dart.weak.outline.expect b/pkg/front_end/testcases/general/external_import.dart.weak.outline.expect
index 046113e..2556da5 100644
--- a/pkg/front_end/testcases/general/external_import.dart.weak.outline.expect
+++ b/pkg/front_end/testcases/general/external_import.dart.weak.outline.expect
@@ -5,17 +5,17 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/general/external_import.dart:7:1: Info: Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK.
+// pkg/front_end/testcases/general/external_import.dart:7:1: Error: Dart native extensions are no longer supported.
 // Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)
 // import 'dart-ext:here';
 // ^
 //
-// pkg/front_end/testcases/general/external_import.dart:8:1: Info: Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK.
+// pkg/front_end/testcases/general/external_import.dart:8:1: Error: Dart native extensions are no longer supported.
 // Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)
 // import 'dart-ext:foo/../there';
 // ^
 //
-// pkg/front_end/testcases/general/external_import.dart:9:1: Info: Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK.
+// pkg/front_end/testcases/general/external_import.dart:9:1: Error: Dart native extensions are no longer supported.
 // Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)
 // import 'dart-ext:/usr/local/somewhere';
 // ^
diff --git a/pkg/front_end/testcases/general/external_import.dart.weak.transformed.expect b/pkg/front_end/testcases/general/external_import.dart.weak.transformed.expect
index b4adba8..0d7662f 100644
--- a/pkg/front_end/testcases/general/external_import.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/general/external_import.dart.weak.transformed.expect
@@ -5,17 +5,17 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/general/external_import.dart:7:1: Info: Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK.
+// pkg/front_end/testcases/general/external_import.dart:7:1: Error: Dart native extensions are no longer supported.
 // Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)
 // import 'dart-ext:here';
 // ^
 //
-// pkg/front_end/testcases/general/external_import.dart:8:1: Info: Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK.
+// pkg/front_end/testcases/general/external_import.dart:8:1: Error: Dart native extensions are no longer supported.
 // Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)
 // import 'dart-ext:foo/../there';
 // ^
 //
-// pkg/front_end/testcases/general/external_import.dart:9:1: Info: Dart native extensions are deprecated and will be removed in the 2.15 release of Dart SDK.
+// pkg/front_end/testcases/general/external_import.dart:9:1: Error: Dart native extensions are no longer supported.
 // Migrate to using FFI instead (https://dart.dev/guides/libraries/c-interop)
 // import 'dart-ext:/usr/local/somewhere';
 // ^
diff --git a/tools/VERSION b/tools/VERSION
index b666881..061b57b 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -27,5 +27,5 @@
 MAJOR 2
 MINOR 15
 PATCH 0
-PRERELEASE 77
+PRERELEASE 78
 PRERELEASE_PATCH 0
\ No newline at end of file