diff --git a/Language/Expressions/Constants/is_not_type_A01_t01.dart b/Language/Expressions/Constants/is_not_type_A01_t01.dart
new file mode 100644
index 0000000000..da52035691
--- /dev/null
+++ b/Language/Expressions/Constants/is_not_type_A01_t01.dart
@@ -0,0 +1,75 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// @assertion A constant expression is an expression whose value can never
+/// change, and that can be evaluated entirely at compile time.
+/// A constant expression is one of the following:
+/// ...
+/// • An expression of the form e is! T is equivalent to !(e is T) in every
+///   way, including whether it’s potentially constant or constant.
+///
+/// @description Checks that an expression of the form `e is! T` is a constant
+/// expression if `e` is a constant expression and `T` is a constant type
+/// expression
+/// @author sgrekhov22@gmail.com
+/// @issue 54620
+
+// SharedOptions=--enable-experiment=inline-class
+
+import "../../../Utils/expect.dart";
+
+class C {
+  const C();
+}
+
+extension type const IntET1(int _) {}
+extension type const IntET2(int _) implements int {}
+
+main() {
+  const c1 = 1 is! num;
+  const c2 = (3.14 as num) is! double;
+  const c3 = IntET1(1) is! int;
+  const c4 = IntET2(1) is! int;
+  const c5 = (IntET1(1),) is! (int,);
+  const c6 = (IntET2(1),) is! (int,);
+  const c7 = [IntET1(1)] is! List<int>;
+  const c8 = [IntET2(1)] is! List<num>;
+  const c9 = {IntET1(1)} is! Set<num>;
+  const c10 = {IntET2(1)} is! Set<num>;
+  const c11 = {IntET1(1): IntET1(2)} is! Map<num, int>;
+  const c12 = {IntET1(1): IntET2(2)} is! Map<num, int>;
+  const c13 = {IntET2(1): IntET1(2)} is! Map<num, int>;
+  const c14 = {IntET2(1): IntET2(2)} is! Map<num, int>;
+  const c15 = 1 is! IntET1;
+  const c16 = 1 is! IntET2;
+  const c17 = IntET1(1) is! IntET2;
+  const c18 = IntET2(1) is! IntET1;
+  const c19 = C() is! Object;
+  const c20 = const C() is! Object;
+  const c21 = () is! ();
+  const c22 = (i: 1) is! ({num i});
+
+  Expect.isFalse(c1);
+  Expect.isFalse(c2);
+  Expect.isFalse(c3);
+  Expect.isFalse(c4);
+  Expect.isFalse(c5);
+  Expect.isFalse(c6);
+  Expect.isFalse(c7);
+  Expect.isFalse(c8);
+  Expect.isFalse(c9);
+  Expect.isFalse(c10);
+  Expect.isFalse(c11);
+  Expect.isFalse(c12);
+  Expect.isFalse(c13);
+  Expect.isFalse(c14);
+  Expect.isFalse(c15);
+  Expect.isFalse(c16);
+  Expect.isFalse(c17);
+  Expect.isFalse(c18);
+  Expect.isFalse(c19);
+  Expect.isFalse(c20);
+  Expect.isFalse(c21);
+  Expect.isFalse(c22);
+}
diff --git a/Language/Expressions/Constants/is_not_type_A01_t02.dart b/Language/Expressions/Constants/is_not_type_A01_t02.dart
new file mode 100644
index 0000000000..8dafeaacb2
--- /dev/null
+++ b/Language/Expressions/Constants/is_not_type_A01_t02.dart
@@ -0,0 +1,96 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// @assertion A constant expression is an expression whose value can never
+/// change, and that can be evaluated entirely at compile time.
+/// A constant expression is one of the following:
+/// ...
+/// • An expression of the form e is! T is equivalent to !(e is T) in every
+///   way, including whether it’s potentially constant or constant.
+/// ...
+/// A constant type expression is one of:
+/// • An simple or qualified identifier denoting a type declaration (a type
+///   alias, class or mixin declaration) that is not qualified by a deferred
+///   prefix, optionally followed by type arguments of the form <T1, ..., Tn>
+///   where T1, ..., Tn are constant type expressions.
+/// • A type of the form FutureOr<T> where T is a constant type expression.
+/// • A function type R Function<typeParameters>(argumentTypes) (where
+///   R and <typeParameters> may be omitted) and where R, typeParameters
+///   and argumentTypes (if present) contain only constant type expressions.
+/// • The type void.
+/// • The type dynamic
+///
+/// @description Checks that an expression of the form `e is! T` is a constant
+/// expression if `e` is a constant expression and `T` is a constant type
+/// expression. Test different constant type expressions
+/// @author sgrekhov22@gmail.com
+/// @issue 54636
+
+// SharedOptions=--enable-experiment=inline-class
+
+import "dart:async";
+import "../../../Utils/expect.dart";
+
+mixin M {}
+
+class C<T> with M {
+  const C();
+}
+
+typedef CNumAlias = C<num>;
+
+enum E {
+  e1, e2;
+}
+
+extension type const IntET1(int _) {}
+extension type const IntET2(int _) implements int {}
+
+typedef IntET1Alias = IntET1;
+typedef IntET2Alias = IntET2;
+
+void foo() {}
+void as() {}
+int bar<T>(T t) => 42;
+
+main() {
+  const c1 = C() is! C;
+  const c2 = C() is! M;
+  const c3 = E.e1 is! E;
+  const c4 = C<int>() is! C<num>;
+  const c5 = C<int>() is! CNumAlias;
+  const c6 = IntET1(1) is! IntET2Alias;
+  const c7 = IntET2(1) is! IntET1Alias;
+
+  const fo1 = C() is! FutureOr<C>;
+  const fo2 = C() is! FutureOr<M>;
+  const fo3 = E.e1 is! FutureOr<E>;
+  const fo4 = C<int>() is! FutureOr<C<num>>;
+  const fo5 = C<int>() is! FutureOr<CNumAlias>;
+  const fo6 = IntET1(1) is! FutureOr<IntET2Alias>;
+  const fo7 = IntET2(1) is! FutureOr<IntET1Alias>;
+
+  const f1 = foo is! void Function();
+  const f2 = bar<int> is! int Function(int);
+
+  const d = 2 is! dynamic;
+
+  Expect.isFalse(c1);
+  Expect.isFalse(c2);
+  Expect.isFalse(c3);
+  Expect.isFalse(c4);
+  Expect.isFalse(c5);
+  Expect.isFalse(c6);
+  Expect.isFalse(c7);
+  Expect.isFalse(fo1);
+  Expect.isFalse(fo2);
+  Expect.isFalse(fo3);
+  Expect.isFalse(fo4);
+  Expect.isFalse(fo5);
+  Expect.isFalse(fo6);
+  Expect.isFalse(fo7);
+  Expect.isFalse(f1);
+  Expect.isFalse(f2);
+  Expect.isFalse(d);
+}
diff --git a/Language/Expressions/Constants/is_not_type_A01_t03.dart b/Language/Expressions/Constants/is_not_type_A01_t03.dart
new file mode 100644
index 0000000000..280bdf52b7
--- /dev/null
+++ b/Language/Expressions/Constants/is_not_type_A01_t03.dart
@@ -0,0 +1,51 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// @assertion A constant expression is an expression whose value can never
+/// change, and that can be evaluated entirely at compile time.
+/// A constant expression is one of the following:
+/// ...
+/// • An expression of the form e is! T is equivalent to !(e is T) in every
+///   way, including whether it’s potentially constant or constant.
+/// ...
+/// A constant type expression is one of:
+/// • An simple or qualified identifier denoting a type declaration (a type
+///   alias, class or mixin declaration) that is not qualified by a deferred
+///   prefix, optionally followed by type arguments of the form <T1, ..., Tn>
+///   where T1, ..., Tn are constant type expressions.
+/// • A type of the form FutureOr<T> where T is a constant type expression.
+/// • A function type R Function<typeParameters>(argumentTypes) (where
+///   R and <typeParameters> may be omitted) and where R, typeParameters
+///   and argumentTypes (if present) contain only constant type expressions.
+/// • The type void.
+/// • The type dynamic
+///
+/// @description Checks that an expression of the form `e is! T` is a constant
+/// expression if `T` is a constant type expression of type `FutureOr<void>` or
+/// an extension type with a representation type `void`
+/// @author sgrekhov22@gmail.com
+/// @issue 54620
+
+// SharedOptions=--enable-experiment=inline-class
+
+import "dart:async";
+import "../../../Utils/expect.dart";
+
+extension type const VoidET(void _) {}
+
+main() {
+  const c1 = 1 is! VoidET;
+  const c2 = 2 is! FutureOr<void>;
+  const c3 = (3,) is! (VoidET,);
+  const c4 = (4,) is! (FutureOr<void>,);
+  const c5 = (i: 5) is! ({VoidET i});
+  const c6 = (i: 6) is! ({FutureOr<void> i});
+
+  Expect.isFalse(c1);
+  Expect.isFalse(c2);
+  Expect.isFalse(c3);
+  Expect.isFalse(c4);
+  Expect.isFalse(c5);
+  Expect.isFalse(c6);
+}
diff --git a/Language/Expressions/Constants/is_not_type_A02_t01.dart b/Language/Expressions/Constants/is_not_type_A02_t01.dart
new file mode 100644
index 0000000000..5250c7c58b
--- /dev/null
+++ b/Language/Expressions/Constants/is_not_type_A02_t01.dart
@@ -0,0 +1,113 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// @assertion A constant expression is an expression whose value can never
+/// change, and that can be evaluated entirely at compile time.
+/// A constant expression is one of the following:
+/// ...
+/// • An expression of the form e is! T is equivalent to !(e is T) in every
+///   way, including whether it’s potentially constant or constant.
+///
+/// @description Checks that an expression of the form `e is! T` is not a
+/// constant expression if `e` is not a constant expression
+/// @author sgrekhov22@gmail.com
+
+// SharedOptions=--enable-experiment=inline-class
+
+class C {
+  C();
+}
+
+extension type IntET1(int _) {}
+extension type IntET2(int _) implements int {}
+
+test<T>() {
+  const c = T is! Type;
+//          ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
+
+main() {
+  int i = 1;
+  var d = 3.14;
+  var c = C();
+
+  const c1 = i is! num;
+//           ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c2 = (d as num) is! double;
+//            ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c3 = IntET1(1) is! int;
+//           ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c4 = IntET2(1) is! int;
+//           ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c5 = (i,) is! (int,);
+//            ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c6 = (IntET1(1),) is! (int,);
+//            ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c7 = (IntET2(1),) is! (int,);
+//            ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c8 = [i] is! List<int>;
+//            ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c9 = [IntET1(1)] is! List<int>;
+//            ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c10 = [IntET2(1)] is! List<num>;
+//             ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c11 = {d} is! Set<num>;
+//             ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c12 = {IntET1(1)} is! Set<num>;
+//             ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c13 = {IntET2(1)} is! Set<num>;
+//             ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c14 = {IntET1(1): IntET1(2)} is! Map<num, int>;
+//             ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c15 = {IntET2(1): IntET2(2)} is! Map<num, int>;
+//             ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c16 = IntET1(1) is! IntET2;
+//            ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c17 = IntET2(1) is! IntET1;
+//            ^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c19 = c is! Object;
+//            ^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const c20 = () {} is! Function;
+//            ^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
diff --git a/Language/Expressions/Constants/is_not_type_A02_t02.dart b/Language/Expressions/Constants/is_not_type_A02_t02.dart
new file mode 100644
index 0000000000..6a0d786432
--- /dev/null
+++ b/Language/Expressions/Constants/is_not_type_A02_t02.dart
@@ -0,0 +1,39 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// @assertion A constant expression is an expression whose value can never
+/// change, and that can be evaluated entirely at compile time.
+/// A constant expression is one of the following:
+/// ...
+/// • An expression of the form e is! T is equivalent to !(e is T) in every
+///   way, including whether it’s potentially constant or constant.
+///
+/// @description Checks that an expression of the form `e is! T` is not a
+/// constant expression if `e` is not an expression
+/// @author sgrekhov22@gmail.com
+
+extension IntExtension on int {}
+
+main() {
+  const Foo = int Function() is! Function;
+//            ^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const Void = void is! Type;
+//             ^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const cIntExtension = IntExtension is! Type;
+//                      ^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const R1 = (void,) is! Type;
+//            ^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+  const R2 = ({int i}) is! Record;
+//                 ^
+// [analyzer] unspecified
+// [cfe] unspecified
+}
diff --git a/Language/Expressions/Constants/is_not_type_A03_t01.dart b/Language/Expressions/Constants/is_not_type_A03_t01.dart
new file mode 100644
index 0000000000..e78d132b46
--- /dev/null
+++ b/Language/Expressions/Constants/is_not_type_A03_t01.dart
@@ -0,0 +1,54 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+/// @assertion A constant expression is an expression whose value can never
+/// change, and that can be evaluated entirely at compile time.
+/// A constant expression is one of the following:
+/// ...
+/// • An expression of the form e is! T is equivalent to !(e is T) in every
+///   way, including whether it’s potentially constant or constant.
+/// ...
+/// A constant type expression is one of:
+/// • An simple or qualified identifier denoting a type declaration (a type
+///   alias, class or mixin declaration) that is not qualified by a deferred
+///   prefix, optionally followed by type arguments of the form <T1, ..., Tn>
+///   where T1, ..., Tn are constant type expressions.
+/// • A type of the form FutureOr<T> where T is a constant type expression.
+/// • A function type R Function<typeParameters>(argumentTypes) (where
+///   R and <typeParameters> may be omitted) and where R, typeParameters
+///   and argumentTypes (if present) contain only constant type expressions.
+/// • The type void.
+/// • The type dynamic
+///
+/// @description Checks that an expression of the form `e is! T` is not a
+/// constant expression if `T` is not a constant type expression
+/// @author sgrekhov22@gmail.com
+
+import "constants_lib.dart" deferred as p;
+
+extension IntExtension on int {}
+
+main() {
+  const Num = num;
+
+  const c1 = 1 is! Num;
+//                 ^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  const c2 = 1 is! p.A;
+//                 ^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  const c3 = 1 is! IntExtension;
+//                 ^^^^^^^^^^^^
+// [analyzer] unspecified
+// [cfe] unspecified
+
+  const c4 = 1 is! 42;
+//                 ^^
+// [analyzer] unspecified
+// [cfe] unspecified
+}