diff --git a/.github/workflows/push_gem.yml b/.github/workflows/push_gem.yml
new file mode 100644
index 0000000..633377c
--- /dev/null
+++ b/.github/workflows/push_gem.yml
@@ -0,0 +1,46 @@
+name: Publish gem to rubygems.org
+
+on:
+  push:
+    tags:
+      - 'v*'
+
+permissions:
+  contents: read
+
+jobs:
+  push:
+    if: github.repository == 'ruby/set'
+    runs-on: ubuntu-latest
+
+    environment:
+      name: rubygems.org
+      url: https://rubygems.org/gems/set
+
+    permissions:
+      contents: write
+      id-token: write
+
+    steps:
+      - name: Harden Runner
+        uses: step-security/harden-runner@f4a75cfd619ee5ce8d5b864b0d183aff3c69b55a # v2.13.1
+        with:
+          egress-policy: audit
+
+      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+
+      - name: Set up Ruby
+        uses: ruby/setup-ruby@e34163cd15f4bb403dcd72d98e295997e6a55798 # v1.238.0
+        with:
+          bundler-cache: true
+          ruby-version: ruby
+
+      - name: Publish to RubyGems
+        uses: rubygems/release-gem@a25424ba2ba8b387abc8ef40807c2c85b96cbe32 # v1.1.1
+
+      - name: Create GitHub release
+        run: |
+          tag_name="$(git describe --tags --abbrev=0)"
+          gh release create "${tag_name}" --verify-tag --generate-notes
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index ece2aae..9e55565 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -3,15 +3,22 @@ name: test
 on: [push, pull_request]
 
 jobs:
+  ruby-versions:
+    uses: ruby/actions/.github/workflows/ruby_versions.yml@master
+    with:
+      engine: cruby
+      min_version: 3.0
+
   build:
+    needs: ruby-versions
     name: build (${{ matrix.ruby }} / ${{ matrix.os }})
     strategy:
       matrix:
-        ruby: [ 3.2, 3.1, "3.0", head ]
+        ruby: ${{ fromJson(needs.ruby-versions.outputs.versions) }}
         os: [ ubuntu-latest, macos-latest ]
     runs-on: ${{ matrix.os }}
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v5
     - name: Set up Ruby
       uses: ruby/setup-ruby@v1
       with:
diff --git a/CHANGELOG.md b/CHANGELOG.md
index a74b2c4..3035be0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Set Changelog
 
+# 1.1.1 (2024-11-29)
+
+* Enhancements
+  * Fix Set#^ to respect subclasses [#38][] ([@kyanagi][])
+  * Speed up Set#flatten [#39][] ([@kyanagi][])
+
 # 1.1.0 (2023-12-23)
 
 * Optimize for and require Ruby >=3
@@ -48,6 +54,8 @@ This is the first release of set as a gem.  Here lists the changes since the ver
 [#20]: https://github.com/ruby/set/pull/20
 [#29]: https://github.com/ruby/set/pull/29
 [#30]: https://github.com/ruby/set/pull/30
+[#38]: https://github.com/ruby/set/pull/38
+[#39]: https://github.com/ruby/set/pull/39
 [Feature #17838]: https://bugs.ruby-lang.org/issues/17838
 [Feature #16989]: https://bugs.ruby-lang.org/issues/16989
 
@@ -56,4 +64,5 @@ This is the first release of set as a gem.  Here lists the changes since the ver
 [@jeremyevans]: https://github.com/jeremyevans
 [@k-tsj]: https://github.com/k-tsj
 [@knu]: https://github.com/knu
+[@kyanagi]: https://github.com/kyanagi
 [@marcandre]: https://github.com/marcandre
diff --git a/LICENSE.txt b/LICENSE.txt
index 6ffacb6..4d4df5b 100644
--- a/LICENSE.txt
+++ b/LICENSE.txt
@@ -1,4 +1,4 @@
-Copyright (c) 2002-2020 Akinori MUSHA
+Copyright (c) 2002-2024 Akinori MUSHA
 
 All rights reserved.
 
diff --git a/lib/set.rb b/lib/set.rb
index 4b706b7..295750f 100644
--- a/lib/set.rb
+++ b/lib/set.rb
@@ -1,9 +1,17 @@
 # frozen_string_literal: true
+
+if RUBY_VERSION >= '3.5'
+  if defined?(Set) && defined?(Set.[]) && Set.method(:[]).source_location.nil?
+    # Remove defined? ... conditional after Ruby 3.5.0-preview2
+    return
+  end
+end
+
 # :markup: markdown
 #
 # set.rb - defines the Set class
 #
-# Copyright (c) 2002-2023 Akinori MUSHA <knu@iDaemons.org>
+# Copyright (c) 2002-2024 Akinori MUSHA <knu@iDaemons.org>
 #
 # Documentation by Akinori MUSHA and Gavin Sinclair.
 #
@@ -216,7 +224,7 @@
 #   has been modified while an element in the set.
 #
 class Set
-  VERSION = "1.1.0"
+  VERSION = "1.1.2"
 
   include Enumerable
 
@@ -335,7 +343,7 @@ def replace(enum)
     end
   end
 
-  # Converts the set to an array.  The order of elements is uncertain.
+  # Returns an array containing all elements in the set.
   #
   #     Set[1, 2].to_a                    #=> [1, 2]
   #     Set[1, 'c', :s].to_a              #=> [1, "c", :s]
@@ -353,16 +361,19 @@ def to_set(klass = Set, *args, &block)
     klass.new(self, *args, &block)
   end
 
-  def flatten_merge(set, seen = Set.new) # :nodoc:
+  def flatten_merge(set, seen = {}) # :nodoc:
     set.each { |e|
       if e.is_a?(Set)
-        if seen.include?(e_id = e.object_id)
+        case seen[e_id = e.object_id]
+        when true
           raise ArgumentError, "tried to flatten recursive Set"
+        when false
+          next
         end
 
-        seen.add(e_id)
+        seen[e_id] = true
         flatten_merge(e, seen)
-        seen.delete(e_id)
+        seen[e_id] = false
       else
         add(e)
       end
@@ -540,22 +551,22 @@ def delete?(o)
   # Deletes every element of the set for which block evaluates to
   # true, and returns self. Returns an enumerator if no block is
   # given.
-  def delete_if
+  def delete_if(&block)
     block_given? or return enum_for(__method__) { size }
-    # @hash.delete_if should be faster, but using it breaks the order
-    # of enumeration in subclasses.
-    select { |o| yield o }.each { |o| @hash.delete(o) }
+    # Instead of directly using @hash.delete_if, perform enumeration
+    # using self.each that subclasses may override.
+    select(&block).each { |o| @hash.delete(o) }
     self
   end
 
   # Deletes every element of the set for which block evaluates to
   # false, and returns self. Returns an enumerator if no block is
   # given.
-  def keep_if
+  def keep_if(&block)
     block_given? or return enum_for(__method__) { size }
-    # @hash.keep_if should be faster, but using it breaks the order of
-    # enumeration in subclasses.
-    reject { |o| yield o }.each { |o| @hash.delete(o) }
+    # Instead of directly using @hash.keep_if, perform enumeration
+    # using self.each that subclasses may override.
+    reject(&block).each { |o| @hash.delete(o) }
     self
   end
 
@@ -659,7 +670,7 @@ def &(enum)
   #     Set[1, 2] ^ Set[2, 3]                   #=> #<Set: {3, 1}>
   #     Set[1, 'b', 'c'] ^ ['b', 'd']           #=> #<Set: {"d", 1, "c"}>
   def ^(enum)
-    n = Set.new(enum)
+    n = self.class.new(enum)
     each { |o| n.add(o) unless n.delete?(o) }
     n
   end
diff --git a/test/test_set.rb b/test/test_set.rb
index 49dc58e..453ace3 100644
--- a/test/test_set.rb
+++ b/test/test_set.rb
@@ -643,6 +643,11 @@ def test_xor
     ret = set ^ [2,4,5,5]
     assert_not_same(set, ret)
     assert_equal(Set[1,3,5], ret)
+
+    set2 = Set2[1,2,3,4]
+    ret2 = set2 ^ [2,4,5,5]
+    assert_instance_of(Set2, ret2)
+    assert_equal(Set2[1,3,5], ret2)
   end
 
   def test_eq
@@ -780,26 +785,54 @@ def test_join
     assert_equal('1 & 2 & 3', Set[1, 2, 3].join(' & '))
   end
 
-  def test_inspect
-    set1 = Set[1, 2]
-    assert_equal('#<Set: {1, 2}>', set1.inspect)
+  if RUBY_VERSION >= '3.5'
+    def test_inspect
+      set1 = Set[1, 2]
+      assert_equal('Set[1, 2]', set1.inspect)
 
-    set2 = Set[Set[0], 1, 2, set1]
-    assert_equal('#<Set: {#<Set: {0}>, 1, 2, #<Set: {1, 2}>}>', set2.inspect)
+      set2 = Set[Set[0], 1, 2, set1]
+      assert_equal('Set[Set[0], 1, 2, Set[1, 2]]', set2.inspect)
 
-    set1.add(set2)
-    assert_equal('#<Set: {#<Set: {0}>, 1, 2, #<Set: {1, 2, #<Set: {...}>}>}>', set2.inspect)
-  end
+      set1.add(set2)
+      assert_equal('Set[Set[0], 1, 2, Set[1, 2, Set[...]]]', set2.inspect)
 
-  def test_to_s
-    set1 = Set[1, 2]
-    assert_equal('#<Set: {1, 2}>', set1.to_s)
+      c = Class.new(Set)
+      c.set_temporary_name("_MySet")
+      assert_equal('_MySet[1, 2]', c[1, 2].inspect)
+    end
+
+    def test_to_s
+      set1 = Set[1, 2]
+      assert_equal('Set[1, 2]', set1.to_s)
+
+      set2 = Set[Set[0], 1, 2, set1]
+      assert_equal('Set[Set[0], 1, 2, Set[1, 2]]', set2.to_s)
 
-    set2 = Set[Set[0], 1, 2, set1]
-    assert_equal('#<Set: {#<Set: {0}>, 1, 2, #<Set: {1, 2}>}>', set2.to_s)
+      set1.add(set2)
+      assert_equal('Set[Set[0], 1, 2, Set[1, 2, Set[...]]]', set2.to_s)
+    end
+  else
+    def test_inspect
+      set1 = Set[1, 2]
+      assert_equal('#<Set: {1, 2}>', set1.inspect)
+
+      set2 = Set[Set[0], 1, 2, set1]
+      assert_equal('#<Set: {#<Set: {0}>, 1, 2, #<Set: {1, 2}>}>', set2.inspect)
+
+      set1.add(set2)
+      assert_equal('#<Set: {#<Set: {0}>, 1, 2, #<Set: {1, 2, #<Set: {...}>}>}>', set2.inspect)
+    end
 
-    set1.add(set2)
-    assert_equal('#<Set: {#<Set: {0}>, 1, 2, #<Set: {1, 2, #<Set: {...}>}>}>', set2.to_s)
+    def test_to_s
+      set1 = Set[1, 2]
+      assert_equal('#<Set: {1, 2}>', set1.to_s)
+
+      set2 = Set[Set[0], 1, 2, set1]
+      assert_equal('#<Set: {#<Set: {0}>, 1, 2, #<Set: {1, 2}>}>', set2.to_s)
+
+      set1.add(set2)
+      assert_equal('#<Set: {#<Set: {0}>, 1, 2, #<Set: {1, 2, #<Set: {...}>}>}>', set2.to_s)
+    end
   end
 
   def test_compare_by_identity
diff --git a/test/test_sorted_set.rb b/test/test_sorted_set.rb
index f7ad7af..09a1e7a 100644
--- a/test/test_sorted_set.rb
+++ b/test/test_sorted_set.rb
@@ -42,4 +42,4 @@ def test_ok_require
       var = SortedSet.new.to_s
     RUBY
   end
-end
+end if defined?(SortedSet)