diff --git a/.github/workflows/sync_default_gems.yml b/.github/workflows/sync_default_gems.yml
index 1a9b43ec5241a9..9ef89f89ff2b05 100644
--- a/.github/workflows/sync_default_gems.yml
+++ b/.github/workflows/sync_default_gems.yml
@@ -59,6 +59,10 @@ jobs:
           git pull --rebase origin ${GITHUB_REF#refs/heads/}
           git push origin ${GITHUB_REF#refs/heads/}
         if: ${{ steps.sync.outputs.update }}
+        env:
+          EMAIL: svn-admin@ruby-lang.org
+          GIT_AUTHOR_NAME: git
+          GIT_COMMITTER_NAME: git
 
       - uses: ./.github/actions/slack
         with:
diff --git a/NEWS.md b/NEWS.md
index 3c2957d032579f..e33408054ea5e4 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -206,7 +206,7 @@ The following default gems are updated.
 * prism 1.6.0
 * psych 5.2.6
 * resolv 0.6.3
-* stringio 3.1.8.dev
+* stringio 3.1.9.dev
 * strscan 3.1.6.dev
 * timeout 0.4.4
 * uri 1.1.1
diff --git a/ext/stringio/stringio.c b/ext/stringio/stringio.c
index 5da0b4c9457a2e..17be72f71a8cb6 100644
--- a/ext/stringio/stringio.c
+++ b/ext/stringio/stringio.c
@@ -13,7 +13,7 @@
 **********************************************************************/
 
 static const char *const
-STRINGIO_VERSION = "3.1.8.dev";
+STRINGIO_VERSION = "3.1.9.dev";
 
 #include <stdbool.h>
 
diff --git a/lib/bundled_gems.rb b/lib/bundled_gems.rb
index 914c8465032fdc..49fb90249dd6ae 100644
--- a/lib/bundled_gems.rb
+++ b/lib/bundled_gems.rb
@@ -20,17 +20,17 @@ module Gem::BUNDLED_GEMS # :nodoc:
     "resolv-replace" => "3.4.0",
     "rinda" => "3.4.0",
     "syslog" => "3.4.0",
-    "ostruct" => "3.5.0",
-    "pstore" => "3.5.0",
-    "rdoc" => "3.5.0",
-    "win32ole" => "3.5.0",
-    "fiddle" => "3.5.0",
-    "logger" => "3.5.0",
-    "benchmark" => "3.5.0",
-    "irb" => "3.5.0",
-    "reline" => "3.5.0",
-    # "readline" => "3.5.0", # This is wrapper for reline. We don't warn for this.
-    "tsort" => "3.6.0",
+    "ostruct" => "4.0.0",
+    "pstore" => "4.0.0",
+    "rdoc" => "4.0.0",
+    "win32ole" => "4.0.0",
+    "fiddle" => "4.0.0",
+    "logger" => "4.0.0",
+    "benchmark" => "4.0.0",
+    "irb" => "4.0.0",
+    "reline" => "4.0.0",
+    # "readline" => "4.0.0", # This is wrapper for reline. We don't warn for this.
+    "tsort" => "4.1.0",
   }.freeze
 
   EXACT = {
diff --git a/lib/error_highlight/core_ext.rb b/lib/error_highlight/core_ext.rb
index e6cacbaf9e832a..1cfc331582748e 100644
--- a/lib/error_highlight/core_ext.rb
+++ b/lib/error_highlight/core_ext.rb
@@ -24,7 +24,7 @@ module CoreExt
               _, _, snippet, highlight = ErrorHighlight.formatter.message_for(spot).lines
               out += "\n    | #{ snippet }      #{ highlight }"
             else
-              out += "\n    (cannot highlight method definition; try Ruby 3.5 or later)"
+              out += "\n    (cannot highlight method definition; try Ruby 4.0 or later)"
             end
           end
           ret << "\n" + out if out
diff --git a/lib/net/http.rb b/lib/net/http.rb
index c60649b8123c09..1a13299d202aa0 100644
--- a/lib/net/http.rb
+++ b/lib/net/http.rb
@@ -2587,7 +2587,7 @@ def debug(msg)
     alias_method :D, :debug
   end
 
-  # for backward compatibility until Ruby 3.5
+  # for backward compatibility until Ruby 4.0
   # https://bugs.ruby-lang.org/issues/20900
   # https://github.com/bblimke/webmock/pull/1081
   HTTPSession = HTTP
diff --git a/numeric.c b/numeric.c
index de5b02aaf9eb41..731a8095239107 100644
--- a/numeric.c
+++ b/numeric.c
@@ -5553,7 +5553,7 @@ rb_int_digits_bigbase(VALUE num, VALUE base)
     }
 
     bases = rb_ary_new();
-    for (VALUE b = base; int_lt(b, num) == Qtrue; b = rb_int_mul(b, b)) {
+    for (VALUE b = base; int_le(b, num) == Qtrue; b = rb_int_mul(b, b)) {
         rb_ary_push(bases, b);
     }
     digits = rb_ary_new_from_args(1, num);
diff --git a/spec/bundled_gems_spec.rb b/spec/bundled_gems_spec.rb
index 8014a48223c8cf..c2a655929ab7bf 100644
--- a/spec/bundled_gems_spec.rb
+++ b/spec/bundled_gems_spec.rb
@@ -113,7 +113,7 @@ def script(code, options = {})
       require "active_support/all"
     RUBY
 
-    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 3.5.0/)
+    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 4.0.0/)
     expect(err).to include(/lib\/active_support\/all\.rb:1/)
   end
 
@@ -159,7 +159,7 @@ def script(code, options = {})
 
     bundle "exec ruby script.rb"
 
-    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 3.5.0/)
+    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 4.0.0/)
     expect(err).to include(/script\.rb:8/)
   end
 
@@ -177,7 +177,7 @@ def script(code, options = {})
 
     bundle "exec ./script.rb"
 
-    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 3.5.0/)
+    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 4.0.0/)
     expect(err).to include(/script\.rb:9/)
   end
 
@@ -186,7 +186,7 @@ def script(code, options = {})
     create_file("Gemfile", "source 'https://rubygems.org'")
     bundle "exec ruby -r./stub -ropenssl -e ''"
 
-    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 3.5.0/)
+    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 4.0.0/)
   end
 
   it "Show warning when warn is not the standard one in the current scope" do
@@ -209,7 +209,7 @@ def my
       My.my
     RUBY
 
-    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 3.5.0/)
+    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 4.0.0/)
     expect(err).to include(/-e:19/)
   end
 
@@ -251,7 +251,7 @@ def my
       require Gem::BUNDLED_GEMS::ARCHDIR + 'openssl'
     RUBY
 
-    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 3.5.0/)
+    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 4.0.0/)
     # TODO: We should assert caller location like below:
     # test_warn_bootsnap.rb:14: warning: ...
   end
@@ -320,7 +320,7 @@ def my
     create_file("Gemfile", "source 'https://rubygems.org'")
     bundle "exec ruby script.rb"
 
-    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 3.5.0/)
+    expect(err).to include(/openssl used to be loaded from (.*) since Ruby 4.0.0/)
     expect(err).to include(/script\.rb:13/)
   end
 
diff --git a/spec/bundler/spec_helper.rb b/spec/bundler/spec_helper.rb
index d750218452ebcf..96cd7be4720a66 100644
--- a/spec/bundler/spec_helper.rb
+++ b/spec/bundler/spec_helper.rb
@@ -27,6 +27,8 @@
 require "rspec/expectations"
 require "rspec/mocks"
 require "rspec/support/differ"
+gem "rubygems-generate_index"
+require "rubygems/indexer"
 
 require_relative "support/builders"
 require_relative "support/checksums"
diff --git a/spec/bundler/support/builders.rb b/spec/bundler/support/builders.rb
index 5ca227cf5b3aa3..1283dc4348821d 100644
--- a/spec/bundler/support/builders.rb
+++ b/spec/bundler/support/builders.rb
@@ -279,14 +279,8 @@ def update_repo(path, build_compact_index: true)
       @_build_path = "#{path}/gems"
       @_build_repo = File.basename(path)
       yield
-      with_gem_path_as scoped_base_system_gem_path do
-        Dir[scoped_base_system_gem_path.join("gems/rubygems-generate_index*/lib")].first ||
-          raise("Could not find rubygems-generate_index lib directory in #{scoped_base_system_gem_path}")
-
-        command = "generate_index"
-        command += " --no-compact" if !build_compact_index && gem_command(command + " --help").include?("--[no-]compact")
-        gem_command command, dir: path
-      end
+      options = { build_compact: build_compact_index }
+      Gem::Indexer.new(path, options).generate_index
     ensure
       @_build_path = nil
       @_build_repo = nil
diff --git a/test/error_highlight/test_error_highlight.rb b/test/error_highlight/test_error_highlight.rb
index 43e232071f9371..1276a0a0d93a7b 100644
--- a/test/error_highlight/test_error_highlight.rb
+++ b/test/error_highlight/test_error_highlight.rb
@@ -1468,7 +1468,7 @@ def test_wrong_number_of_arguments_for_method
       MethodDefLocationSupported ?
    "|   def wrong_number_of_arguments_test(x, y)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^" :
-   "(cannot highlight method definition; try Ruby 3.5 or later)"
+   "(cannot highlight method definition; try Ruby 4.0 or later)"
    }
     END
 
@@ -1494,7 +1494,7 @@ def test_missing_keyword
       MethodDefLocationSupported ?
    "|   def keyword_test(kw1:, kw2:, kw3:)
             ^^^^^^^^^^^^" :
-   "(cannot highlight method definition; try Ruby 3.5 or later)"
+   "(cannot highlight method definition; try Ruby 4.0 or later)"
    }
     END
 
@@ -1515,7 +1515,7 @@ def test_missing_keywords # multiple missing keywords
       MethodDefLocationSupported ?
    "|   def keyword_test(kw1:, kw2:, kw3:)
             ^^^^^^^^^^^^" :
-   "(cannot highlight method definition; try Ruby 3.5 or later)"
+   "(cannot highlight method definition; try Ruby 4.0 or later)"
    }
     END
 
@@ -1536,7 +1536,7 @@ def test_unknown_keyword
       MethodDefLocationSupported ?
    "|   def keyword_test(kw1:, kw2:, kw3:)
             ^^^^^^^^^^^^" :
-   "(cannot highlight method definition; try Ruby 3.5 or later)"
+   "(cannot highlight method definition; try Ruby 4.0 or later)"
    }
     END
 
@@ -1557,7 +1557,7 @@ def test_unknown_keywords
       MethodDefLocationSupported ?
    "|   def keyword_test(kw1:, kw2:, kw3:)
             ^^^^^^^^^^^^" :
-   "(cannot highlight method definition; try Ruby 3.5 or later)"
+   "(cannot highlight method definition; try Ruby 4.0 or later)"
    }
     END
 
@@ -1587,7 +1587,7 @@ def test_wrong_number_of_arguments_for_method2
       MethodDefLocationSupported ?
    "|   def wrong_number_of_arguments_test2(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^" :
-   "(cannot highlight method definition; try Ruby 3.5 or later)"
+   "(cannot highlight method definition; try Ruby 4.0 or later)"
    }
     END
 
@@ -1609,7 +1609,7 @@ def test_wrong_number_of_arguments_for_lambda_literal
       MethodDefLocationSupported ?
    "|     v = -> {}
               ^^" :
-   "(cannot highlight method definition; try Ruby 3.5 or later)"
+   "(cannot highlight method definition; try Ruby 4.0 or later)"
    }
     END
 
@@ -1631,7 +1631,7 @@ def test_wrong_number_of_arguments_for_lambda_method
       MethodDefLocationSupported ?
    "|     v = lambda { }
                      ^" :
-   "(cannot highlight method definition; try Ruby 3.5 or later)"
+   "(cannot highlight method definition; try Ruby 4.0 or later)"
    }
     END
 
@@ -1657,7 +1657,7 @@ def test_wrong_number_of_arguments_for_define_method
       MethodDefLocationSupported ?
    "|   define_method :define_method_test do |x, y|
                                           ^^" :
-   "(cannot highlight method definition; try Ruby 3.5 or later)"
+   "(cannot highlight method definition; try Ruby 4.0 or later)"
    }
     END
 
diff --git a/test/ruby/test_bignum.rb b/test/ruby/test_bignum.rb
index dd6f4baa4c292b..c366f794b2a1f5 100644
--- a/test/ruby/test_bignum.rb
+++ b/test/ruby/test_bignum.rb
@@ -821,6 +821,9 @@ def test_digits
     assert_equal([7215, 2413, 6242], T1024P.digits(10_000).first(3))
     assert_equal([11], 11.digits(T1024P))
     assert_equal([T1024P - 1, 1], (T1024P + T1024P - 1).digits(T1024P))
+    bug21680 = '[ruby-core:123769] [Bug #21680]'
+    assert_equal([0] * 64 + [1], (2**512).digits(256), bug21680)
+    assert_equal([0] * 128 + [1], (123**128).digits(123), bug21680)
   end
 
   def test_digits_for_negative_numbers
diff --git a/tool/bundler/dev_gems.rb b/tool/bundler/dev_gems.rb
index 0d4dbd7f2ee058..0039a42171aa41 100644
--- a/tool/bundler/dev_gems.rb
+++ b/tool/bundler/dev_gems.rb
@@ -12,6 +12,7 @@
 gem "rspec-core", "~> 3.12"
 gem "rspec-expectations", "~> 3.12"
 gem "rspec-mocks", "~> 3.12"
+gem "rubygems-generate_index", "~> 1.1"
 
 group :doc do
   gem "ronn-ng", "~> 0.10.1", platform: :ruby
diff --git a/tool/bundler/dev_gems.rb.lock b/tool/bundler/dev_gems.rb.lock
index bc1d2acfc98da8..7f73c43f4cc1dd 100644
--- a/tool/bundler/dev_gems.rb.lock
+++ b/tool/bundler/dev_gems.rb.lock
@@ -1,6 +1,7 @@
 GEM
   remote: https://rubygems.org/
   specs:
+    compact_index (0.15.0)
     diff-lcs (1.6.1)
     kramdown (2.5.1)
       rexml (>= 3.3.9)
@@ -54,6 +55,8 @@ GEM
       diff-lcs (>= 1.2.0, < 2.0)
       rspec-support (~> 3.13.0)
     rspec-support (3.13.2)
+    rubygems-generate_index (1.1.3)
+      compact_index (~> 0.15.0)
     test-unit (3.6.7)
       power_assert
     turbo_tests (2.2.5)
@@ -83,10 +86,12 @@ DEPENDENCIES
   rspec-core (~> 3.12)
   rspec-expectations (~> 3.12)
   rspec-mocks (~> 3.12)
+  rubygems-generate_index (~> 1.1)
   test-unit (~> 3.0)
   turbo_tests (~> 2.2.3)
 
 CHECKSUMS
+  compact_index (0.15.0) sha256=5c6c404afca8928a7d9f4dde9524f6e1610db17e675330803055db282da84a8b
   diff-lcs (1.6.1) sha256=12a5a83f3e37a8e2f4427268e305914d5f1879f22b4e73bb1a09f76a3dd86cd4
   kramdown (2.5.1) sha256=87bbb6abd9d3cebe4fc1f33e367c392b4500e6f8fa19dd61c0972cf4afe7368c
   kramdown-parser-gfm (1.1.0) sha256=fb39745516427d2988543bf01fc4cf0ab1149476382393e0e9c48592f6581729
@@ -115,6 +120,7 @@ CHECKSUMS
   rspec-expectations (3.13.3) sha256=0e6b5af59b900147698ea0ff80456c4f2e69cac4394fbd392fbd1ca561f66c58
   rspec-mocks (3.13.2) sha256=2327335def0e1665325a9b617e3af9ae20272741d80ac550336309a7c59abdef
   rspec-support (3.13.2) sha256=cea3a2463fd9b84b9dcc9685efd80ea701aa8f7b3decb3b3ce795ed67737dbec
+  rubygems-generate_index (1.1.3) sha256=3571424322666598e9586a906485e1543b617f87644913eaf137d986a3393f5c
   test-unit (3.6.7) sha256=c342bb9f7334ea84a361b43c20b063f405c0bf3c7dbe3ff38f61a91661d29221
   turbo_tests (2.2.5) sha256=3fa31497d12976d11ccc298add29107b92bda94a90d8a0a5783f06f05102509f