diff --git a/CHANGELOG.md b/CHANGELOG.md
index b12aaa9..9d292a6b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,32 +4,43 @@
 * Allow using URI strings in `part of` declarations to refer to the
   importing library.
 
-### Core library changes
+#### Strong Mode
 
-* `dart:core`
-  * Added `Uri.isScheme` function to check the scheme of a URI.
-    Example: `uri.isScheme("http")`. Ignores case when comparing.
-  * Make `UriData.parse` validate its input better.
-    If the data is base-64 encoded, the data is normalized wrt.
-    alphabet and padding, and it contains invalid base-64 data,
-    parsing fails. Also normalizes non-base-64 data.
-* `dart:io`
-  * Added functions `File.lastAccessed`, `File.lastAccessedSync`,
-    `File.setLastModified`, `File.setLastModifiedSync`, `File.setLastAccessed`,
-    and `File.setLastAccessedSync`.
-  * Added `{Stdin,Stdout}.supportsAnsiEscapes`.
+* Breaking change - it is now a strong mode error if a mixin causes a name
+  conflict between two private members (field/getter/setter/method) from a
+  different library. (SDK
+  issue [28809](https://github.com/dart-lang/sdk/issues/28809)).
 
-### Dart VM
+lib1.dart:
 
-* Calls to `print()` and `Stdout.write*()` now correctly print unicode
-  characters to the console on Windows. Calls to `Stdout.add*()` behave as
-  before.
 
-### Strong Mode
+```dart
+class A {
+  int _x;
+}
 
-* Strong mode will prefer the expected type to infer generic types,
-  functions, and methods
-  (SDK issue [27586](https://github.com/dart-lang/sdk/issues/27586)).
+class B {
+  int _x;
+}
+```
+
+lib2.dart:
+
+
+```dart
+import 'lib1.dart';
+
+class C extends A with B {}
+```
+
+```
+    error • The private name _x, defined by B, conflicts with the same name defined by A at tmp/lib2.dart:3:24 • private_collision_in_mixin_application
+```
+
+
+* Breaking change - strong mode will prefer the expected type to infer generic
+  types, functions, and methods (SDK
+  issue [27586](https://github.com/dart-lang/sdk/issues/27586)).
 
   ```dart
   main() {
@@ -75,6 +86,49 @@
     }
     ```
 
+* Strong mode down cast composite warnings are no longer issued by default.
+  (SDK issue [28588](https://github.com/dart-lang/sdk/issues/28588)).
+
+```dart
+void test() {
+  List untyped = [];
+  List<int> typed = untyped; // No down cast composite warning
+}
+```
+
+To opt back into the warnings, add the following to
+the
+[.analysis_options](https://www.dartlang.org/guides/language/analysis-options)
+file for your project.
+
+```
+analyzer:
+  errors:
+    strong_mode_down_cast_composite: warning
+```
+
+
+### Core library changes
+
+* `dart:core`
+  * Added `Uri.isScheme` function to check the scheme of a URI.
+    Example: `uri.isScheme("http")`. Ignores case when comparing.
+  * Make `UriData.parse` validate its input better.
+    If the data is base-64 encoded, the data is normalized wrt.
+    alphabet and padding, and it contains invalid base-64 data,
+    parsing fails. Also normalizes non-base-64 data.
+* `dart:io`
+  * Added functions `File.lastAccessed`, `File.lastAccessedSync`,
+    `File.setLastModified`, `File.setLastModifiedSync`, `File.setLastAccessed`,
+    and `File.setLastAccessedSync`.
+  * Added `{Stdin,Stdout}.supportsAnsiEscapes`.
+
+### Dart VM
+
+* Calls to `print()` and `Stdout.write*()` now correctly print unicode
+  characters to the console on Windows. Calls to `Stdout.add*()` behave as
+  before.
+
 ### Tool changes
 
 * Analysis
diff --git a/pkg/analyzer/lib/dart/element/element.dart b/pkg/analyzer/lib/dart/element/element.dart
index 853cf84..b348a15 100644
--- a/pkg/analyzer/lib/dart/element/element.dart
+++ b/pkg/analyzer/lib/dart/element/element.dart
@@ -1329,10 +1329,26 @@
 
 /**
  * The pseudo-declaration that defines a generic function type.
+ *
+ * Clients may not extend, implement, or mix-in this class.
  */
 abstract class GenericFunctionTypeElement implements FunctionTypedElement {}
 
 /**
+ * A [FunctionTypeAliasElement] whose returned function type has a [type]
+ * parameter.
+ *
+ * Clients may not extend, implement, or mix-in this class.
+ */
+abstract class GenericTypeAliasElement implements FunctionTypeAliasElement {
+  /**
+   * Return the generic function type element representing the generic function
+   * type on the right side of the equals.
+   */
+  GenericFunctionTypeElement get function;
+}
+
+/**
  * A combinator that causes some of the names in a namespace to be hidden when
  * being imported.
  *
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 7ce5826..ea9a428 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -5029,7 +5029,7 @@
  */
 class GenericTypeAliasElementImpl extends ElementImpl
     with TypeParameterizedElementMixin
-    implements FunctionTypeAliasElement {
+    implements GenericTypeAliasElement {
   /**
    * The unlinked representation of the type in the summary.
    */
@@ -5097,10 +5097,7 @@
   CompilationUnitElementImpl get enclosingUnit =>
       _enclosingElement as CompilationUnitElementImpl;
 
-  /**
-   * Return the generic function type element representing the generic function
-   * type on the right side of the equals.
-   */
+  @override
   GenericFunctionTypeElement get function {
     if (_function == null && _unlinkedTypedef != null) {
       DartType type = enclosingUnit.resynthesizerContext.resolveTypeRef(
diff --git a/pkg/analyzer/lib/src/error/codes.dart b/pkg/analyzer/lib/src/error/codes.dart
index f650d54..df5e5ee 100644
--- a/pkg/analyzer/lib/src/error/codes.dart
+++ b/pkg/analyzer/lib/src/error/codes.dart
@@ -4951,46 +4951,51 @@
       "Type parameter bound types must be instantiated.",
       "Try adding type arguments.");
 
+  /*
+   * TODO(brianwilkerson) Make the TOP_LEVEL_ error codes be errors rather than
+   * hints and then clean up the function _errorSeverity in
+   * test/src/task/strong/strong_test_helper.dart.
+   */
   static const StrongModeCode TOP_LEVEL_CYCLE = const StrongModeCode(
-      ErrorType.COMPILE_TIME_ERROR,
+      ErrorType.HINT,
       'TOP_LEVEL_CYCLE',
       "The type of '{0}' can't be inferred because it depends on itself through the cycle: {1}.",
       "Try adding an explicit type to one or more of the variables in the cycle in order to break the cycle.");
 
   static const StrongModeCode TOP_LEVEL_FUNCTION_LITERAL_BLOCK =
       const StrongModeCode(
-          ErrorType.COMPILE_TIME_ERROR,
+          ErrorType.HINT,
           'TOP_LEVEL_FUNCTION_LITERAL_BLOCK',
           "The type of the function literal can't be inferred because the literal has a block as its body.",
           "Try adding an explicit type to the variable.");
 
   static const StrongModeCode TOP_LEVEL_FUNCTION_LITERAL_PARAMETER =
       const StrongModeCode(
-          ErrorType.COMPILE_TIME_ERROR,
+          ErrorType.HINT,
           'TOP_LEVEL_FUNCTION_LITERAL_PARAMETER',
           "The type of '{0}' can't be inferred because the parameter '{1}' does not have an explicit type.",
           "Try adding an explicit type to the parameter '{1}', or add an explicit type for '{0}'.");
 
   static const StrongModeCode TOP_LEVEL_IDENTIFIER_NO_TYPE = const StrongModeCode(
-      ErrorType.COMPILE_TIME_ERROR,
+      ErrorType.HINT,
       'TOP_LEVEL_IDENTIFIER_NO_TYPE',
       "The type of '{0}' can't be inferred because the type of '{1}' couldn't be inferred.",
       "Try adding an explicit type to either the variable '{0}' or the variable '{1}'.");
 
   static const StrongModeCode TOP_LEVEL_INSTANCE_GETTER = const StrongModeCode(
-      ErrorType.COMPILE_TIME_ERROR,
+      ErrorType.HINT,
       'TOP_LEVEL_INSTANCE_GETTER',
       "The type of '{0}' can't be inferred because of the use of the instance getter '{1}'.",
       "Try removing the use of the instance getter {1}, or add an explicit type for '{0}'.");
 
   static const StrongModeCode TOP_LEVEL_TYPE_ARGUMENTS = const StrongModeCode(
-      ErrorType.COMPILE_TIME_ERROR,
+      ErrorType.HINT,
       'TOP_LEVEL_TYPE_ARGUMENTS',
       "The type of '{0}' can't be inferred because type arguments were not given for '{1}'.",
       "Try adding type arguments for '{1}', or add an explicit type for '{0}'.");
 
   static const StrongModeCode TOP_LEVEL_UNSUPPORTED = const StrongModeCode(
-      ErrorType.COMPILE_TIME_ERROR,
+      ErrorType.HINT,
       'TOP_LEVEL_UNSUPPORTED',
       "The type of '{0}' can't be inferred because {1} expressions aren't supported.",
       "Try adding an explicit type for '{0}'.");
diff --git a/pkg/analyzer/lib/src/task/strong/checker.dart b/pkg/analyzer/lib/src/task/strong/checker.dart
index 463a5c2..91134c2 100644
--- a/pkg/analyzer/lib/src/task/strong/checker.dart
+++ b/pkg/analyzer/lib/src/task/strong/checker.dart
@@ -1047,7 +1047,13 @@
     var severity =
         (processor != null) ? processor.severity : errorCode.errorSeverity;
 
-    if (severity == ErrorSeverity.ERROR) _failure = true;
+    if (severity == ErrorSeverity.ERROR) {
+      _failure = true;
+    }
+    if (errorCode.type == ErrorType.HINT &&
+        errorCode.name.startsWith('STRONG_MODE_TOP_LEVEL_')) {
+      severity = ErrorSeverity.ERROR;
+    }
     if (severity != ErrorSeverity.INFO || _options.strongModeHints) {
       int begin = node is AnnotatedNode
           ? node.firstTokenAfterCommentAndMetadata.offset
diff --git a/pkg/analyzer/test/generated/hint_code_test.dart b/pkg/analyzer/test/generated/hint_code_test.dart
index fd3bf9d..93ea7b3 100644
--- a/pkg/analyzer/test/generated/hint_code_test.dart
+++ b/pkg/analyzer/test/generated/hint_code_test.dart
@@ -2499,22 +2499,6 @@
     verify([source]);
   }
 
-  test_strongMode_downCastCompositeNoHint() async {
-    AnalysisOptionsImpl options = new AnalysisOptionsImpl();
-    options.strongMode = true;
-    options.strongModeHints = false;
-    resetWith(options: options);
-    Source source = addSource(r'''
-main() {
-  List dynamicList = [ ];
-  List<int> list = dynamicList;
-  print(list);
-}''');
-    await computeAnalysisResult(source);
-    assertNoErrors(source);
-    verify([source]);
-  }
-
   test_strongMode_downCastCompositeHint() async {
     AnalysisOptionsImpl options = new AnalysisOptionsImpl();
     options.strongMode = true;
@@ -2531,6 +2515,22 @@
     verify([source]);
   }
 
+  test_strongMode_downCastCompositeNoHint() async {
+    AnalysisOptionsImpl options = new AnalysisOptionsImpl();
+    options.strongMode = true;
+    options.strongModeHints = false;
+    resetWith(options: options);
+    Source source = addSource(r'''
+main() {
+  List dynamicList = [ ];
+  List<int> list = dynamicList;
+  print(list);
+}''');
+    await computeAnalysisResult(source);
+    assertNoErrors(source);
+    verify([source]);
+  }
+
   test_strongMode_downCastCompositeWarn() async {
     AnalysisOptionsImpl options = new AnalysisOptionsImpl();
     applyToAnalysisOptions(options, {
@@ -2554,6 +2554,20 @@
     verify([source]);
   }
 
+  test_strongMode_topLevelInstanceGetter() async {
+    resetWith(options: new AnalysisOptionsImpl()..strongMode = true);
+    Source source = addSource(r'''
+class A {
+  int get g => 0;
+}
+var a = new A();
+var b = a.g;
+''');
+    await computeAnalysisResult(source);
+    assertErrors(source, [StrongModeCode.TOP_LEVEL_INSTANCE_GETTER]);
+    verify([source]);
+  }
+
   test_typeCheck_type_is_Null() async {
     Source source = addSource(r'''
 m(i) {
diff --git a/pkg/analyzer/test/src/task/strong/strong_test_helper.dart b/pkg/analyzer/test/src/task/strong/strong_test_helper.dart
index dddce07..77f38a3 100644
--- a/pkg/analyzer/test/src/task/strong/strong_test_helper.dart
+++ b/pkg/analyzer/test/src/task/strong/strong_test_helper.dart
@@ -67,6 +67,11 @@
 
 ErrorSeverity _errorSeverity(
     AnalysisOptions analysisOptions, AnalysisError error) {
+  // TODO(brianwilkerson) Remove the if when top-level inference is made an
+  // error again.
+  if (error.errorCode.name.startsWith('STRONG_MODE_TOP_LEVEL_')) {
+    return ErrorSeverity.ERROR;
+  }
   return ErrorProcessor.getProcessor(analysisOptions, error)?.severity ??
       error.errorCode.errorSeverity;
 }
diff --git a/tests/corelib_strong/corelib_strong.status b/tests/corelib_strong/corelib_strong.status
index 5e5c511..04e0e1a 100644
--- a/tests/corelib_strong/corelib_strong.status
+++ b/tests/corelib_strong/corelib_strong.status
@@ -56,4 +56,4 @@
 uri_query_test: Skip
 
 [ $compiler == dart2analyzer && $strong ]
-error_stack_trace2_test: CompileTimeError
+# error_stack_trace2_test: CompileTimeError
diff --git a/tests/language_strong/language_strong.status b/tests/language_strong/language_strong.status
index 52448d8..03fe136 100644
--- a/tests/language_strong/language_strong.status
+++ b/tests/language_strong/language_strong.status
@@ -682,20 +682,20 @@
 wrong_number_type_arguments_test: Skip
 
 [ $compiler == dart2analyzer && $strong ]
-async_await_test/02: CompileTimeError # Issue 28823
-async_await_test/03: CompileTimeError # Issue 28823
-async_await_test/none: CompileTimeError # Issue 28823
-async_star_test/01: CompileTimeError # Issue 28823
-async_star_test/02: CompileTimeError # Issue 28823
-async_star_test/03: CompileTimeError # Issue 28823
-async_star_test/04: CompileTimeError # Issue 28823
-async_star_test/05: CompileTimeError # Issue 28823
-async_star_test/none: CompileTimeError # Issue 28823
+# async_await_test/02: CompileTimeError # Issue 28823
+# async_await_test/03: CompileTimeError # Issue 28823
+# async_await_test/none: CompileTimeError # Issue 28823
+# async_star_test/01: CompileTimeError # Issue 28823
+# async_star_test/02: CompileTimeError # Issue 28823
+# async_star_test/03: CompileTimeError # Issue 28823
+# async_star_test/04: CompileTimeError # Issue 28823
+# async_star_test/05: CompileTimeError # Issue 28823
+# async_star_test/none: CompileTimeError # Issue 28823
 bit_operations_test/01: MissingStaticWarning # Issue 28823
 bit_operations_test/02: MissingStaticWarning # Issue 28823
 bit_operations_test/03: MissingStaticWarning # Issue 28823
 bit_operations_test/04: MissingStaticWarning # Issue 28823
-closure_side_effect_test: CompileTimeError # Issue 28823
+# closure_side_effect_test: CompileTimeError # Issue 28823
 constant_type_literal_test/01: MissingCompileTimeError # Issue 28823
 field3a_negative_test: StaticWarning # Issue 28823
 generic_methods_overriding_test/01: MissingCompileTimeError # Issue 29070
@@ -704,7 +704,7 @@
 generic_methods_closure_test: CompileTimeError # Issue 29070
 generic_methods_simple_is_expression_test: CompileTimeError # Issue 29070
 generic_methods_local_variable_declaration_test: CompileTimeError # Issue 29070
-inferrer_constructor3_test: CompileTimeError
+# inferrer_constructor3_test: CompileTimeError
 interface_inherit_field_test: StaticWarning # Issue 28823
 internal_library_test/02: MissingStaticWarning # Issue 28823
 main_not_a_function_test/01: MissingStaticWarning # Issue 28823
diff --git a/tests/lib_strong/lib_strong.status b/tests/lib_strong/lib_strong.status
index 8ada277..ea25758 100644
--- a/tests/lib_strong/lib_strong.status
+++ b/tests/lib_strong/lib_strong.status
@@ -138,6 +138,6 @@
 html/custom/document_register_type_extensions_test: CompileTimeError # Issue 28969
 html/custom/element_upgrade_test: CompileTimeError # Issue 28969
 html/debugger_test: CompileTimeError # Issue 28969
-html/input_element_test: CompileTimeError
+# html/input_element_test: CompileTimeError
 html/js_typed_interop_default_arg_test/default_value: MissingCompileTimeError # Issue 28969
 mirrors/deferred_mirrors_metadata_test: StaticWarning # Issue 28969
diff --git a/tools/VERSION b/tools/VERSION
index fa7e810..4c6934a 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -28,4 +28,4 @@
 MINOR 23
 PATCH 0
 PRERELEASE 11
-PRERELEASE_PATCH 0
+PRERELEASE_PATCH 1