diff --git a/bootstraptest/test_ractor.rb b/bootstraptest/test_ractor.rb
index a72d6b34970..7388e0bb31a 100644
--- a/bootstraptest/test_ractor.rb
+++ b/bootstraptest/test_ractor.rb
@@ -1277,20 +1277,6 @@ assert_equal 'Ractor::IsolationError', %q{
   res
 }
 
-# Class#initialize writes the superclass of an uninitialized class, so it is
-# owner-only like any other modification
-assert_equal 'can not modify K because it is created by another Ractor', %q{
-  K = Class.allocate
-
-  r = Ractor.new { K.send(:initialize, Struct) }
-
-  begin
-    r.join
-  rescue Ractor::RemoteError => e
-    e.cause.message
-  end
-}
-
 # Module#refine writes its refinement tables into the receiver, so the receiver
 # must be owned too
 assert_equal 'can not modify M because it is created by another Ractor', %q{
diff --git a/object.c b/object.c
index caf6b723462..a14094f8e69 100644
--- a/object.c
+++ b/object.c
@@ -2200,15 +2200,16 @@ rb_mod_initialize_clone(int argc, VALUE* argv, VALUE clone)
  *  want to treat it like a regular class.
  */
 
+/* :nodoc: */
 static VALUE
-rb_class_initialize(int argc, VALUE *argv, VALUE klass)
+rb_class_s_new(int argc, VALUE *argv, VALUE self)
 {
     VALUE super;
+    VALUE klass;
 
-    // an uninitialized class is still somebody's, and this writes its superclass
-    rb_class_modify_check(klass);
-    if (RCLASS_SUPER(klass) != 0 || klass == rb_cBasicObject) {
-        rb_raise(rb_eTypeError, "already initialized class");
+    // #<Class:Class> is an ancestor of every metaclass, so this also receives Foo.singleton_class.new
+    if (self != rb_cClass) {
+        rb_raise(rb_eTypeError, "can't create instance of singleton class");
     }
     if (rb_check_arity(argc, 0, 1) == 0) {
         super = rb_cObject;
@@ -2220,6 +2221,7 @@ rb_class_initialize(int argc, VALUE *argv, VALUE klass)
             rb_raise(rb_eTypeError, "can't inherit uninitialized class");
         }
     }
+    klass = rb_class_s_alloc(self);
     rb_class_set_super(klass, super);
     RCLASS_SET_MAX_IV_COUNT(klass, RCLASS_MAX_IV_COUNT(super));
     RCLASS_SET_ALLOCATOR(klass, RCLASS_ALLOCATOR(super));
@@ -2231,6 +2233,23 @@ rb_class_initialize(int argc, VALUE *argv, VALUE klass)
     return klass;
 }
 
+/* :nodoc: */
+static VALUE
+rb_class_dup(VALUE self)
+{
+    VALUE dup = rb_class_s_alloc(rb_obj_class(self));
+    return rb_obj_dup_setup(self, dup);
+}
+
+/* :nodoc: */
+static VALUE
+rb_class_clone(int argc, VALUE *argv, VALUE self)
+{
+    VALUE kwfreeze = rb_get_freeze_opt(argc, argv);
+    VALUE clone = rb_class_s_alloc(rb_obj_class(self));
+    return rb_obj_clone_setup(self, clone, kwfreeze);
+}
+
 /*! \private */
 void
 rb_undefined_alloc(VALUE klass)
@@ -4691,11 +4710,13 @@ InitVM_Object(void)
     rb_define_method(rb_singleton_class(rb_cClass), "allocate", rb_class_alloc, 0);
     rb_define_method(rb_cClass, "allocate", rb_class_alloc, 0);
     rb_define_method(rb_cClass, "new", rb_class_new_instance_pass_kw, -1);
-    rb_define_method(rb_cClass, "initialize", rb_class_initialize, -1);
     rb_define_method(rb_cClass, "superclass", rb_class_superclass, 0);
     rb_define_method(rb_cClass, "subclasses", rb_class_subclasses, 0); /* in class.c */
     rb_define_method(rb_cClass, "attached_object", rb_class_attached_object, 0); /* in class.c */
-    rb_define_alloc_func(rb_cClass, rb_class_s_alloc);
+    rb_define_singleton_method(rb_cClass, "new", rb_class_s_new, -1);
+    rb_define_method(rb_cClass, "dup", rb_class_dup, 0);
+    rb_define_method(rb_cClass, "clone", rb_class_clone, -1);
+    rb_undef_alloc_func(rb_cClass);
     rb_undef_method(rb_cClass, "extend_object");
     rb_undef_method(rb_cClass, "append_features");
     rb_undef_method(rb_cClass, "prepend_features");
diff --git a/spec/ruby/core/class/allocate_spec.rb b/spec/ruby/core/class/allocate_spec.rb
index b8950a678ec..b9e8d49758e 100644
--- a/spec/ruby/core/class/allocate_spec.rb
+++ b/spec/ruby/core/class/allocate_spec.rb
@@ -6,19 +6,6 @@ describe "Class#allocate" do
     klass.allocate.should.instance_of?(klass)
   end
 
-  it "returns a fully-formed instance of Module" do
-    klass = Class.allocate
-    klass.constants.should_not == nil
-    klass.methods.should_not == nil
-  end
-
-  it "throws an exception when calling a method on a new instance" do
-    klass = Class.allocate
-    -> do
-      klass.new
-    end.should.raise(Exception)
-  end
-
   it "does not call initialize on the new instance" do
     klass = Class.new do
       def initialize(*args)
@@ -33,9 +20,30 @@ describe "Class#allocate" do
     klass.allocate.should_not.initialized?
   end
 
-  it "raises TypeError for #superclass" do
-    -> do
-      Class.allocate.superclass
-    end.should.raise(TypeError)
+  ruby_version_is ""..."4.1" do
+    it "returns a fully-formed instance of Module" do
+      klass = Class.allocate
+      klass.constants.should_not == nil
+      klass.methods.should_not == nil
+    end
+
+    it "throws an exception when calling a method on a new instance" do
+      klass = Class.allocate
+      -> do
+        klass.new
+      end.should.raise(Exception)
+    end
+
+    it "raises TypeError for #superclass" do
+      -> do
+        Class.allocate.superclass
+      end.should.raise(TypeError)
+    end
+  end
+
+  ruby_version_is "4.1" do
+    it "raises TypeError when called on Class itself" do
+      -> { Class.allocate }.should.raise(TypeError)
+    end
   end
 end
diff --git a/spec/ruby/core/class/initialize_spec.rb b/spec/ruby/core/class/initialize_spec.rb
index ab8f0a157e6..cd68644fcb6 100644
--- a/spec/ruby/core/class/initialize_spec.rb
+++ b/spec/ruby/core/class/initialize_spec.rb
@@ -1,34 +1,45 @@
 require_relative '../../spec_helper'
 
-describe "Class#initialize" do
-  it "is private" do
-    Class.private_methods(false).should.include?(:initialize)
-  end
-
-  it "raises a TypeError when called on already initialized classes" do
-    ->{
-      Integer.send :initialize
-    }.should.raise(TypeError)
-
-    ->{
-      Object.send :initialize
-    }.should.raise(TypeError)
-  end
-
-  # See [redmine:2601]
-  it "raises a TypeError when called on BasicObject" do
-    ->{
-      BasicObject.send :initialize
-    }.should.raise(TypeError)
-  end
-
-  describe "when given the Class" do
-    before :each do
-      @uninitialized = Class.allocate
+ruby_version_is ""..."4.1" do
+  describe "Class#initialize" do
+    it "is private" do
+      Class.private_methods(false).should.include?(:initialize)
     end
 
-    it "raises a TypeError" do
-      ->{@uninitialized.send(:initialize, Class)}.should.raise(TypeError)
+    it "raises a TypeError when called on already initialized classes" do
+      ->{
+        Integer.send :initialize
+      }.should.raise(TypeError)
+
+      ->{
+        Object.send :initialize
+      }.should.raise(TypeError)
+    end
+
+    # See [redmine:2601]
+    it "raises a TypeError when called on BasicObject" do
+      ->{
+        BasicObject.send :initialize
+      }.should.raise(TypeError)
+    end
+
+    describe "when given the Class" do
+      before :each do
+        @uninitialized = Class.allocate
+      end
+
+      it "raises a TypeError" do
+        ->{@uninitialized.send(:initialize, Class)}.should.raise(TypeError)
+      end
+    end
+  end
+end
+
+ruby_version_is "4.1" do
+  describe "Class#initialize" do
+    it "is not defined" do
+      Class.private_instance_methods(false).should_not.include?(:initialize)
+      Class.instance_methods(false).should_not.include?(:initialize)
     end
   end
 end
diff --git a/test/ruby/test_class.rb b/test/ruby/test_class.rb
index ce305536223..a5d715c47a7 100644
--- a/test/ruby/test_class.rb
+++ b/test/ruby/test_class.rb
@@ -83,12 +83,6 @@ class TestClass < Test::Unit::TestCase
     assert_nil(Class.new <=> 1)
   end
 
-  def test_class_initialize
-    assert_raise(TypeError) do
-      Class.new.instance_eval { initialize }
-    end
-  end
-
   def test_instantiate_singleton_class
     c = class << Object.new; self; end
     assert_raise(TypeError) { c.new }
@@ -317,24 +311,18 @@ class TestClass < Test::Unit::TestCase
   end
 
   def test_uninitialized
-    assert_raise(TypeError) { Class.allocate.new }
-    assert_raise(TypeError) { Class.allocate.superclass }
-    bug6863 = '[ruby-core:47148]'
-    assert_raise(TypeError, bug6863) { Class.new(Class.allocate) }
+    assert_raise(TypeError) { Class.allocate }
 
     allocator = Class.instance_method(:allocate)
+    assert_raise(TypeError) { allocator.bind_call(Class) }
     assert_nothing_raised { allocator.bind(Rational).call }
     assert_nothing_raised { allocator.bind_call(Rational) }
   end
 
-  def test_uninitialized_with_singleton_class
-    c = Class.allocate
-    c.singleton_class
-    assert_raise(TypeError) { c.new }
-  end
-
-  def test_uninitialized_dup
-    assert_raise(TypeError) { Class.allocate.dup.new }
+  def test_singleton_class_new
+    assert_raise_with_message(TypeError, /singleton class/) { Integer.singleton_class.new }
+    assert_raise_with_message(TypeError, /singleton class/) { Class.new.singleton_class.new }
+    assert_raise_with_message(TypeError, /singleton class/) { Class.singleton_class.new }
   end
 
   def test_nonascii_name
diff --git a/tool/rbs_skip_tests b/tool/rbs_skip_tests
index 6c19e73c792..5e1d64d6211 100644
--- a/tool/rbs_skip_tests
+++ b/tool/rbs_skip_tests
@@ -42,6 +42,9 @@ test_TOPDIR(RbConfigSingletonTest) `TOPDIR` is `nil` during CI while RBS type is
 # Failing because ObjectSpace.count_nodes has been removed
 test_count_nodes(ObjectSpaceTest)
 
+# Class#initialize has been removed
+test_initialize(ClassInstanceTest)
+
 ## Unknown failures
 
 # NoMethodError: undefined method 'inspect' for an instance of RBS::UnitTest::Convertibles::ToInt