diff --git a/.github/workflows/ubuntu.yml b/.github/workflows/ubuntu.yml
index 2ed27e278b1dd4..b8e5af7f0f6e65 100644
--- a/.github/workflows/ubuntu.yml
+++ b/.github/workflows/ubuntu.yml
@@ -208,7 +208,7 @@ jobs:
       matrix:
         include:
           # Using the same setup as ZJIT jobs
-          - bench_opts: '--warmup=1 --bench=1 --excludes=lobsters'
+          - bench_opts: '--warmup=1 --bench=1 --excludes=lobsters,shipit'
 
     runs-on: ubuntu-24.04
 
diff --git a/.github/workflows/zjit-macos.yml b/.github/workflows/zjit-macos.yml
index aa3c08b9d8dbc6..820fa91f1a1e90 100644
--- a/.github/workflows/zjit-macos.yml
+++ b/.github/workflows/zjit-macos.yml
@@ -158,7 +158,7 @@ jobs:
         include:
           # Test --call-threshold=2 with 2 iterations in total
           - ruby_opts: '--zjit-call-threshold=2'
-            bench_opts: '--warmup=1 --bench=1 --excludes=lobsters'
+            bench_opts: '--warmup=1 --bench=1 --excludes=lobsters,shipit'
             configure: '--enable-zjit=dev_nodebug' # --enable-zjit=dev is too slow
 
     runs-on: macos-14
diff --git a/.github/workflows/zjit-ubuntu.yml b/.github/workflows/zjit-ubuntu.yml
index f79c1c5b1d2121..d3e954bd723cb8 100644
--- a/.github/workflows/zjit-ubuntu.yml
+++ b/.github/workflows/zjit-ubuntu.yml
@@ -215,7 +215,7 @@ jobs:
         include:
           # Test --call-threshold=2 with 2 iterations in total
           - ruby_opts: '--zjit-call-threshold=2'
-            bench_opts: '--warmup=1 --bench=1 --excludes=lobsters'
+            bench_opts: '--warmup=1 --bench=1 --excludes=lobsters,shipit'
             configure: '--enable-zjit=dev_nodebug' # --enable-zjit=dev is too slow
 
     runs-on: ubuntu-24.04
diff --git a/bootstraptest/test_ractor.rb b/bootstraptest/test_ractor.rb
index e2a3e8dd5beff1..9242dce7dcb6b4 100644
--- a/bootstraptest/test_ractor.rb
+++ b/bootstraptest/test_ractor.rb
@@ -803,7 +803,7 @@ def ractor_local_globals
 }
 
 # given block Proc will be isolated, so can not access outer variables.
-assert_equal 'ArgumentError', %q{
+assert_equal 'Ractor::IsolationError', %q{
   begin
     a = true
     r = Ractor.new do
diff --git a/doc/language/ractor.md b/doc/language/ractor.md
index a0acaf3a918e1a..1592656217678f 100644
--- a/doc/language/ractor.md
+++ b/doc/language/ractor.md
@@ -97,10 +97,10 @@ This isolation occurs at Ractor creation time (when `Ractor.new` is called). If
 begin
   a = true
   r = Ractor.new do
-    a #=> ArgumentError because this block accesses outer variable `a`.
+    a #=> Ractor::IsolationError because this block accesses outer variable `a`.
   end
   r.join # wait for ractor to finish
-rescue ArgumentError
+rescue Ractor::IsolationError
 end
 ```
 
diff --git a/doc/stringio/each_byte.rdoc b/doc/stringio/each_byte.rdoc
index 65e81c53a7cd0f..708432b69e0892 100644
--- a/doc/stringio/each_byte.rdoc
+++ b/doc/stringio/each_byte.rdoc
@@ -7,10 +7,7 @@ returns +self+:
   strio.each_byte {|byte| bytes.push(byte) }
   strio.eof? # => true
   bytes # => [104, 101, 108, 108, 111]
-  bytes = []
-  strio = StringIO.new('тест')      # Four 2-byte characters.
-  strio.each_byte {|byte| bytes.push(byte) }
-  bytes # => [209, 130, 208, 181, 209, 129, 209, 130]
+
   bytes = []
   strio = StringIO.new('こんにちは')  # Five 3-byte characters.
   strio.each_byte {|byte| bytes.push(byte) }
diff --git a/doc/stringio/each_char.rdoc b/doc/stringio/each_char.rdoc
index d0b5e4082cc4d3..bec5ecac3ff454 100644
--- a/doc/stringio/each_char.rdoc
+++ b/doc/stringio/each_char.rdoc
@@ -7,10 +7,7 @@ returns +self+:
   strio.each_char {|char| chars.push(char) }
   strio.eof? # => true
   chars      # => ["h", "e", "l", "l", "o"]
-  chars = []
-  strio = StringIO.new('тест')
-  strio.each_char {|char| chars.push(char) }
-  chars      # => ["т", "е", "с", "т"]
+
   chars = []
   strio = StringIO.new('こんにちは')
   strio.each_char {|char| chars.push(char) }
diff --git a/doc/stringio/each_codepoint.rdoc b/doc/stringio/each_codepoint.rdoc
index ede16de599cf0c..0d10831142ab64 100644
--- a/doc/stringio/each_codepoint.rdoc
+++ b/doc/stringio/each_codepoint.rdoc
@@ -9,10 +9,7 @@ Each codepoint is the integer value for a character; returns self:
   strio.each_codepoint {|codepoint| codepoints.push(codepoint) }
   strio.eof? # => true
   codepoints # => [104, 101, 108, 108, 111]
-  codepoints = []
-  strio = StringIO.new('тест')
-  strio.each_codepoint {|codepoint| codepoints.push(codepoint) }
-  codepoints # => [1090, 1077, 1089, 1090]
+
   codepoints = []
   strio = StringIO.new('こんにちは')
   strio.each_codepoint {|codepoint| codepoints.push(codepoint) }
diff --git a/doc/stringio/getbyte.rdoc b/doc/stringio/getbyte.rdoc
index 5e524941bca4ae..148455abf48f23 100644
--- a/doc/stringio/getbyte.rdoc
+++ b/doc/stringio/getbyte.rdoc
@@ -14,13 +14,6 @@ Returns +nil+ if at end-of-stream:
 
 Returns a byte, not a character:
 
-  s = 'Привет'
-  s.bytes
-  # => [208, 159, 209, 128, 208, 184, 208, 178, 208, 181, 209, 130]
-  strio = StringIO.new(s)
-  strio.getbyte # => 208
-  strio.getbyte # => 159
-
   s = 'こんにちは'
   s.bytes
   # => [227, 129, 147, 227, 130, 147, 227, 129, 171, 227, 129, 161, 227, 129, 175]
diff --git a/doc/stringio/getc.rdoc b/doc/stringio/getc.rdoc
index b2ab46843c8466..58ce47c33790ce 100644
--- a/doc/stringio/getc.rdoc
+++ b/doc/stringio/getc.rdoc
@@ -12,10 +12,6 @@ Returns +nil+ if at end-of-stream:
 
 Returns characters, not bytes:
 
-  strio = StringIO.new('Привет')
-  strio.getc # => "П"
-  strio.getc # => "р"
-
   strio = StringIO.new('こんにちは')
   strio.getc # => "こ"
   strio.getc # => "ん"
diff --git a/doc/stringio/gets.rdoc b/doc/stringio/gets.rdoc
index bbefeb008ae245..4152152a25239e 100644
--- a/doc/stringio/gets.rdoc
+++ b/doc/stringio/gets.rdoc
@@ -19,10 +19,10 @@ With no arguments given, reads a line using the default record separator
   strio.eof? # => true
   strio.gets # => nil
 
-  strio = StringIO.new('Привет')  # Six 2-byte characters
+  strio = StringIO.new('こんにちは')  # Five 3-byte characters.
   strio.pos  # => 0
-  strio.gets # => "Привет"
-  strio.pos  # => 12
+  strio.gets # => "こんにちは"
+  strio.pos  # => 15
 
 <b>Argument +sep+</b>
 
@@ -67,11 +67,11 @@ but in other cases the position may be anywhere:
 
 The position need not be at a character boundary:
 
-  strio = StringIO.new('Привет') # Six 2-byte characters.
-  strio.pos = 2                  # At beginning of second character.
-  strio.gets # => "ривет"
-  strio.pos = 3                  # In middle of second character.
-  strio.gets # => "\x80ивет"
+  strio = StringIO.new('こんにちは')  # Five 3-byte characters.
+  strio.pos = 3                     # At beginning of second character.
+  strio.gets  # => "んにちは"
+  strio.pos = 4                     # Within second character.
+  strio.gets  # => "\x82\x93にちは"
 
 <b>Special Record Separators</b>
 
diff --git a/doc/stringio/size.rdoc b/doc/stringio/size.rdoc
index 9323adf8c3783a..253c612c438fab 100644
--- a/doc/stringio/size.rdoc
+++ b/doc/stringio/size.rdoc
@@ -1,5 +1,4 @@
 Returns the number of bytes in the string in +self+:
 
   StringIO.new('hello').size     # => 5  # Five 1-byte characters.
-  StringIO.new('тест').size      # => 8  # Four 2-byte characters.
   StringIO.new('こんにちは').size # => 15 # Five 3-byte characters.
diff --git a/doc/stringio/stringio.md b/doc/stringio/stringio.md
index ce7872f98af401..f81f79cfea728a 100644
--- a/doc/stringio/stringio.md
+++ b/doc/stringio/stringio.md
@@ -409,13 +409,15 @@ strio.pos = 24
 strio.gets   # => "Fourth line\n"
 strio.pos    # => 36
 
-strio = StringIO.new('тест') # Four 2-byte characters.
-strio.pos = 0 # At first byte of first character.
-strio.read    # => "тест"
-strio.pos = 1 # At second byte of first character.
-strio.read    # => "\x82ест"
-strio.pos = 2 # At first of second character.
-strio.read    # => "ест"
+strio = StringIO.new('こんにちは')  # Five 3-byte characters.
+strio.pos = 0  # At first byte of first character.
+strio.read     # => "こんにちは"
+strio.pos = 1  # At second byte of first character.
+strio.read     # => "\x81\x93んにちは"
+strio.pos = 2  # At third byte of first character.
+strio.read     # => "\x93んにちは"
+strio.pos = 3  # At first byte of second character.
+strio.read     # => "んにちは"
 
 strio = StringIO.new(TEXT)
 strio.pos = 15
diff --git a/lib/bundler/cli.rb b/lib/bundler/cli.rb
index 1f6a65ca57aedd..0f234f26b956b1 100644
--- a/lib/bundler/cli.rb
+++ b/lib/bundler/cli.rb
@@ -155,6 +155,10 @@ def self.default_command(meth = nil)
     def help(cli = nil)
       cli = self.class.all_aliases[cli] if self.class.all_aliases[cli]
 
+      if Bundler.settings[:plugins] && Bundler::Plugin.command?(cli) && !self.class.all_commands.key?(cli)
+        return Bundler::Plugin.exec_command(cli, ["--help"])
+      end
+
       case cli
       when "gemfile" then command = "gemfile"
       when nil       then command = "bundle"
diff --git a/lib/bundler/cli/gem.rb b/lib/bundler/cli/gem.rb
index 236ce530eccb75..79344314fe4950 100644
--- a/lib/bundler/cli/gem.rb
+++ b/lib/bundler/cli/gem.rb
@@ -158,6 +158,9 @@ def run
       case config[:ci]
       when "github"
         templates.merge!("github/workflows/main.yml.tt" => ".github/workflows/main.yml")
+        if extension == "rust"
+          templates.merge!("github/workflows/build-gems.yml.tt" => ".github/workflows/build-gems.yml")
+        end
         config[:ignore_paths] << ".github/"
       when "gitlab"
         templates.merge!("gitlab-ci.yml.tt" => ".gitlab-ci.yml")
@@ -228,6 +231,7 @@ def run
         templates.merge!(
           "Cargo.toml.tt" => "Cargo.toml",
           "ext/newgem/Cargo.toml.tt" => "ext/#{name}/Cargo.toml",
+          "ext/newgem/build.rs.tt" => "ext/#{name}/build.rs",
           "ext/newgem/extconf-rust.rb.tt" => "ext/#{name}/extconf.rb",
           "ext/newgem/src/lib.rs.tt" => "ext/#{name}/src/lib.rs",
         )
@@ -435,6 +439,10 @@ def ensure_safe_gem_name(name, constant_array)
         exit 1
       end
 
+      if /[A-Z]/.match?(name)
+        Bundler.ui.warn "Gem names with capital letters are not recommended. Please use only lowercase letters, numbers, and hyphens."
+      end
+
       constant_name = constant_array.join("::")
 
       existing_constant = constant_array.inject(Object) do |c, s|
diff --git a/lib/bundler/definition.rb b/lib/bundler/definition.rb
index 3cf9fbe8bf03aa..4c0c33753526b5 100644
--- a/lib/bundler/definition.rb
+++ b/lib/bundler/definition.rb
@@ -1125,11 +1125,24 @@ def preload_git_source_worker
     end
 
     def preload_git_sources
-      sources.git_sources.each {|source| preload_git_source_worker.enq(source) }
+      needed_git_sources.each {|source| preload_git_source_worker.enq(source) }
     ensure
       preload_git_source_worker.stop
     end
 
+    # Git sources needed for the requested groups (excludes sources only used by --without groups)
+    def needed_git_sources
+      needed_deps = dependencies_for(requested_groups)
+      sources.git_sources.select do |source|
+        needed_deps.any? {|d| d.source == source }
+      end
+    end
+
+    # Git sources that should be excluded (only used by --without groups)
+    def excluded_git_sources
+      sources.git_sources - needed_git_sources
+    end
+
     def find_source_requirements
       if Gem.ruby_version >= Gem::Version.new("3.3")
         # Ruby 3.2 has a bug that incorrectly triggers a circular dependency warning. This version will continue to
@@ -1141,10 +1154,10 @@ def find_source_requirements
       # specs will be available later when the resolver knows where to
       # look for that gemspec (or its dependencies)
       source_requirements = if precompute_source_requirements_for_indirect_dependencies?
-        all_requirements = source_map.all_requirements
+        all_requirements = source_map.all_requirements(excluded_git_sources)
         { default: default_source }.merge(all_requirements)
       else
-        { default: Source::RubygemsAggregate.new(sources, source_map) }.merge(source_map.direct_requirements)
+        { default: Source::RubygemsAggregate.new(sources, source_map, excluded_git_sources) }.merge(source_map.direct_requirements)
       end
       source_requirements.merge!(source_map.locked_requirements) if nothing_changed?
       metadata_dependencies.each do |dep|
diff --git a/lib/bundler/source/rubygems_aggregate.rb b/lib/bundler/source/rubygems_aggregate.rb
index 99ef81ad54bded..8aeaa375fa37b7 100644
--- a/lib/bundler/source/rubygems_aggregate.rb
+++ b/lib/bundler/source/rubygems_aggregate.rb
@@ -5,9 +5,10 @@ class Source
     class RubygemsAggregate
       attr_reader :source_map, :sources
 
-      def initialize(sources, source_map)
+      def initialize(sources, source_map, excluded_sources = [])
         @sources = sources
         @source_map = source_map
+        @excluded_sources = excluded_sources
 
         @index = build_index
       end
@@ -31,6 +32,8 @@ def build_index
           dependency_names = source_map.pinned_spec_names
 
           sources.all_sources.each do |source|
+            next if @excluded_sources.include?(source)
+
             source.dependency_names = dependency_names - source_map.pinned_spec_names(source)
             idx.add_source source.specs
             dependency_names.concat(source.unmet_deps).uniq!
diff --git a/lib/bundler/source_map.rb b/lib/bundler/source_map.rb
index cb88caf1bd1124..513eb37f8bf347 100644
--- a/lib/bundler/source_map.rb
+++ b/lib/bundler/source_map.rb
@@ -14,10 +14,14 @@ def pinned_spec_names(skip = nil)
       direct_requirements.reject {|_, source| source == skip }.keys
     end
 
-    def all_requirements
+    def all_requirements(excluded_sources = [])
       requirements = direct_requirements.dup
 
-      unmet_deps = sources.non_default_explicit_sources.map do |source|
+      explicit_sources = sources.non_default_explicit_sources.reject do |source|
+        excluded_sources.include?(source)
+      end
+
+      unmet_deps = explicit_sources.map do |source|
         (source.spec_names - pinned_spec_names).each do |indirect_dependency_name|
           previous_source = requirements[indirect_dependency_name]
           if previous_source.nil?
diff --git a/lib/bundler/templates/newgem/Cargo.toml.tt b/lib/bundler/templates/newgem/Cargo.toml.tt
index f5a460c9bbf72e..cd00f97e5a8247 100644
--- a/lib/bundler/templates/newgem/Cargo.toml.tt
+++ b/lib/bundler/templates/newgem/Cargo.toml.tt
@@ -5,3 +5,9 @@
 [workspace]
 members = ["./ext/<%= config[:name] %>"]
 resolver = "2"
+
+[profile.release]
+# By default, debug symbols are stripped from the final binary which makes it
+# harder to debug if something goes wrong. It's recommended to keep debug
+# symbols in the release build so that you can debug the final binary if needed.
+debug = true
diff --git a/lib/bundler/templates/newgem/ext/newgem/Cargo.toml.tt b/lib/bundler/templates/newgem/ext/newgem/Cargo.toml.tt
index c0dc63fbfa3abd..a06166aee7cbe0 100644
--- a/lib/bundler/templates/newgem/ext/newgem/Cargo.toml.tt
+++ b/lib/bundler/templates/newgem/ext/newgem/Cargo.toml.tt
@@ -13,3 +13,10 @@ crate-type = ["cdylib"]
 
 [dependencies]
 magnus = { version = "0.8.2" }
+rb-sys = { version = "0.9", features = ["stable-api-compiled-fallback"] }
+
+[build-dependencies]
+rb-sys-env = "0.2.2"
+
+[dev-dependencies]
+rb-sys-test-helpers = { version = "0.2.2" }
diff --git a/lib/bundler/templates/newgem/ext/newgem/build.rs.tt b/lib/bundler/templates/newgem/ext/newgem/build.rs.tt
new file mode 100644
index 00000000000000..80a78427533f8e
--- /dev/null
+++ b/lib/bundler/templates/newgem/ext/newgem/build.rs.tt
@@ -0,0 +1,5 @@
+pub fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let _ = rb_sys_env::activate()?;
+
+    Ok(())
+}
diff --git a/lib/bundler/templates/newgem/ext/newgem/src/lib.rs.tt b/lib/bundler/templates/newgem/ext/newgem/src/lib.rs.tt
index ba234529a3e8c5..09ce97682d316b 100644
--- a/lib/bundler/templates/newgem/ext/newgem/src/lib.rs.tt
+++ b/lib/bundler/templates/newgem/ext/newgem/src/lib.rs.tt
@@ -1,7 +1,7 @@
 use magnus::{function, prelude::*, Error, Ruby};
 
-fn hello(subject: String) -> String {
-    format!("Hello from Rust, {subject}!")
+pub fn hello(subject: String) -> String {
+    format!("Hello {subject}, from Rust!")
 }
 
 #[magnus::init]
@@ -10,3 +10,14 @@ fn init(ruby: &Ruby) -> Result<(), Error> {
     module.define_singleton_method("hello", function!(hello, 1))?;
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use rb_sys_test_helpers::ruby_test;
+    use super::hello;
+
+    #[ruby_test]
+    fn test_hello() {
+        assert_eq!("Hello world, from Rust!", hello("world".to_string()));
+    }
+}
diff --git a/lib/bundler/templates/newgem/github/workflows/build-gems.yml.tt b/lib/bundler/templates/newgem/github/workflows/build-gems.yml.tt
new file mode 100644
index 00000000000000..c3fca937f6124e
--- /dev/null
+++ b/lib/bundler/templates/newgem/github/workflows/build-gems.yml.tt
@@ -0,0 +1,65 @@
+---
+name: Build gems
+
+on:
+  push:
+    tags:
+      - "v*"
+      - "cross-gem/*"
+  workflow_dispatch:
+
+jobs:
+  ci-data:
+    runs-on: ubuntu-latest
+    outputs:
+      result: ${{ steps.fetch.outputs.result }}
+    steps:
+      - uses: oxidize-rb/actions/fetch-ci-data@v1
+        id: fetch
+        with:
+          supported-ruby-platforms: |
+            exclude: ["arm-linux", "x64-mingw32"]
+          stable-ruby-versions: |
+            exclude: ["head"]
+
+  source-gem:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
+
+      - name: Build gem
+        run: bundle exec rake build
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: source-gem
+          path: pkg/*.gem
+
+  cross-gem:
+    name: Compile native gem for ${{ matrix.platform }}
+    runs-on: ubuntu-latest
+    needs: ci-data
+    strategy:
+      matrix:
+        platform: ${{ fromJSON(needs.ci-data.outputs.result).supported-ruby-platforms }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: ruby/setup-ruby@v1
+        with:
+          bundler-cache: true
+
+      - uses: oxidize-rb/actions/cross-gem@v1
+        id: cross-gem
+        with:
+          platform: ${{ matrix.platform }}
+          ruby-versions: ${{ join(fromJSON(needs.ci-data.outputs.result).stable-ruby-versions, ',') }}
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: cross-gem
+          path: ${{ steps.cross-gem.outputs.gem-path }}
diff --git a/lib/bundler/templates/newgem/newgem.gemspec.tt b/lib/bundler/templates/newgem/newgem.gemspec.tt
index 513875fd63ef07..7799dbfd32f021 100644
--- a/lib/bundler/templates/newgem/newgem.gemspec.tt
+++ b/lib/bundler/templates/newgem/newgem.gemspec.tt
@@ -15,10 +15,6 @@ Gem::Specification.new do |spec|
   spec.license = "MIT"
 <%- end -%>
   spec.required_ruby_version = ">= <%= config[:required_ruby_version] %>"
-<%- if config[:ext] == 'rust' -%>
-  spec.required_rubygems_version = ">= <%= config[:rust_builder_required_rubygems_version] %>"
-<%- end -%>
-
   spec.metadata["allowed_push_host"] = "TODO: Set to your gem server 'https://example.com'"
   spec.metadata["homepage_uri"] = spec.homepage
   spec.metadata["source_code_uri"] = "<%= config[:source_code_uri] %>"
@@ -44,9 +40,6 @@ Gem::Specification.new do |spec|
 
   # Uncomment to register a new dependency of your gem
   # spec.add_dependency "example-gem", "~> 1.0"
-<%- if config[:ext] == 'rust' -%>
-  spec.add_dependency "rb_sys", "~> 0.9.91"
-<%- end -%>
 <%- if config[:ext] == 'go' -%>
   spec.add_dependency "go_gem", "~> 0.2"
 <%- end -%>
diff --git a/lib/bundler/templates/newgem/spec/newgem_spec.rb.tt b/lib/bundler/templates/newgem/spec/newgem_spec.rb.tt
index 82cada988cd3a8..dd39342f788590 100644
--- a/lib/bundler/templates/newgem/spec/newgem_spec.rb.tt
+++ b/lib/bundler/templates/newgem/spec/newgem_spec.rb.tt
@@ -5,7 +5,15 @@ RSpec.describe <%= config[:constant_name] %> do
     expect(<%= config[:constant_name] %>::VERSION).not_to be nil
   end
 
+<%- if config[:ext] == 'rust' -%>
+  it "can call into Rust" do
+    result = <%= config[:constant_name] %>.hello("world")
+
+    expect(result).to be("Hello earth, from Rust!")
+  end
+<%- else -%>
   it "does something useful" do
     expect(false).to eq(true)
   end
+<%- end -%>
 end
diff --git a/lib/bundler/templates/newgem/test/minitest/test_newgem.rb.tt b/lib/bundler/templates/newgem/test/minitest/test_newgem.rb.tt
index 4b35a630714d33..9a859fa4d1eda2 100644
--- a/lib/bundler/templates/newgem/test/minitest/test_newgem.rb.tt
+++ b/lib/bundler/templates/newgem/test/minitest/test_newgem.rb.tt
@@ -7,7 +7,13 @@ class <%= config[:minitest_constant_name] %> < Minitest::Test
     refute_nil ::<%= config[:constant_name] %>::VERSION
   end
 
+<%- if config[:ext] == 'rust' -%>
+  def test_hello_world
+    assert_equal "Hello earth, from Rust!", <%= config[:constant_name] %>.hello("world")
+  end
+<%- else -%>
   def test_it_does_something_useful
     assert false
   end
+<%- end -%>
 end
diff --git a/lib/rubygems/config_file.rb b/lib/rubygems/config_file.rb
index f2c90cce3cb76a..d34480f4743871 100644
--- a/lib/rubygems/config_file.rb
+++ b/lib/rubygems/config_file.rb
@@ -47,8 +47,7 @@ class Gem::ConfigFile
   DEFAULT_CONCURRENT_DOWNLOADS = 8
   DEFAULT_CERT_EXPIRATION_LENGTH_DAYS = 365
   DEFAULT_IPV4_FALLBACK_ENABLED = false
-  # TODO: Use false as default value for this option in RubyGems 4.0
-  DEFAULT_INSTALL_EXTENSION_IN_LIB = true
+  DEFAULT_INSTALL_EXTENSION_IN_LIB = false
   DEFAULT_GLOBAL_GEM_CACHE = false
 
   ##
diff --git a/ractor.rb b/ractor.rb
index ac04237fc6e4f1..2dc60f5ff64926 100644
--- a/ractor.rb
+++ b/ractor.rb
@@ -15,7 +15,7 @@
 #     a = 1
 #     r = Ractor.new {puts "I am in Ractor! a=#{a}"}
 #     # fails immediately with
-#     # ArgumentError (can not isolate a Proc because it accesses outer variables (a).)
+#     # Ractor::IsolationError (can not isolate a Proc because it accesses outer variables (a).)
 #
 # The object must be explicitly shared:
 #     a = 1
@@ -657,7 +657,7 @@ def unmonitor port
   #
   #     a = 42
   #     Ractor.shareable_proc{ p a }
-  #     #=> can not isolate a Proc because it accesses outer variables (a). (ArgumentError)
+  #     #=> can not isolate a Proc because it accesses outer variables (a). (Ractor::IsolationError)
   #
   # The value of `self` in the Proc must be a shareable object.
   #
diff --git a/spec/bundler/commands/newgem_spec.rb b/spec/bundler/commands/newgem_spec.rb
index 06c226f9e56a17..754dd3f31f3f24 100644
--- a/spec/bundler/commands/newgem_spec.rb
+++ b/spec/bundler/commands/newgem_spec.rb
@@ -1733,12 +1733,11 @@ def create_temporary_dir(dir)
         expect(bundled_app("#{gem_name}/ext/#{gem_name}/Cargo.toml")).to exist
         expect(bundled_app("#{gem_name}/ext/#{gem_name}/extconf.rb")).to exist
         expect(bundled_app("#{gem_name}/ext/#{gem_name}/src/lib.rs")).to exist
+        expect(bundled_app("#{gem_name}/ext/#{gem_name}/build.rs")).to exist
       end
 
-      it "includes rake-compiler, rb_sys gems and required_rubygems_version constraint" do
+      it "includes rake-compiler constraint" do
         expect(bundled_app("#{gem_name}/Gemfile").read).to include('gem "rake-compiler"')
-        expect(bundled_app("#{gem_name}/#{gem_name}.gemspec").read).to include('spec.add_dependency "rb_sys"')
-        expect(bundled_app("#{gem_name}/#{gem_name}.gemspec").read).to include('spec.required_rubygems_version = ">= ')
       end
 
       it "depends on compile task for build" do
@@ -1761,6 +1760,30 @@ def create_temporary_dir(dir)
 
         expect(bundled_app("#{gem_name}/Rakefile").read).to eq(rakefile)
       end
+
+      it "configures the crate such that `cargo test` works", :ruby_repo, :mri_only do
+        env = setup_rust_env
+        gem_path = bundled_app(gem_name)
+        result = sys_exec("cargo test", env: env, dir: gem_path)
+
+        expect(result).to include("1 passed")
+      end
+
+      def setup_rust_env
+        skip "rust toolchain of mingw is broken" if RUBY_PLATFORM.match?("mingw")
+
+        env = {
+          "CARGO_HOME" => ENV.fetch("CARGO_HOME", File.join(ENV["HOME"], ".cargo")),
+          "RUSTUP_HOME" => ENV.fetch("RUSTUP_HOME", File.join(ENV["HOME"], ".rustup")),
+          "RUSTUP_TOOLCHAIN" => ENV.fetch("RUSTUP_TOOLCHAIN", "stable"),
+        }
+
+        system(env, "cargo", "-V", out: IO::NULL, err: [:child, :out])
+        skip "cargo not present" unless $?.success?
+        # Hermetic Cargo setup
+        RbConfig::CONFIG.each {|k, v| env["RBCONFIG_#{k}"] = v }
+        env
+      end
     end
 
     context "--ext parameter set with go" do
@@ -1982,6 +2005,19 @@ def create_temporary_dir(dir)
       it { expect(err).to include("Invalid gem name #{subject}") }
     end
 
+    context "starting with a number" do
+      subject { "1gem" }
+      it { expect(err).to include("Invalid gem name #{subject}") }
+    end
+
+    context "including capital letter" do
+      subject { "CAPITAL" }
+      it "should warn but not error" do
+        expect(err).to include("Gem names with capital letters are not recommended")
+        expect(bundled_app("#{subject}/#{subject}.gemspec")).to exist
+      end
+    end
+
     context "starting with an existing const name" do
       subject { "gem-somenewconstantname" }
       it { expect(err).not_to include("Invalid gem name #{subject}") }
diff --git a/spec/bundler/install/git_spec.rb b/spec/bundler/install/git_spec.rb
index aa707a022290e7..b711f6e614082f 100644
--- a/spec/bundler/install/git_spec.rb
+++ b/spec/bundler/install/git_spec.rb
@@ -290,4 +290,32 @@
       end
     end
   end
+
+  describe "with excluded groups" do
+    it "works if you exclude a group with a git gem", ruby: ">= 3.3" do
+      build_git "production_gem", "1.0"
+      build_git "development_gem", "1.0"
+
+      gemfile <<-G
+        source "https://gem.repo1"
+
+        gem "production_gem", :git => "#{lib_path("production_gem-1.0")}"
+
+        group :development do
+          gem "development_gem", :git => "#{lib_path("development_gem-1.0")}"
+        end
+      G
+
+      # First install all groups to create lockfile
+      bundle :install
+
+      # Set without and reinstall
+      bundle "config set --local without development"
+      bundle :install
+
+      # Verify only production gem is available
+      expect(the_bundle).to include_gems("production_gem 1.0")
+      expect(the_bundle).not_to include_gems("development_gem 1.0")
+    end
+  end
 end
diff --git a/spec/bundler/plugins/command_spec.rb b/spec/bundler/plugins/command_spec.rb
index f8dacb0e51eec6..05d535a70cefc3 100644
--- a/spec/bundler/plugins/command_spec.rb
+++ b/spec/bundler/plugins/command_spec.rb
@@ -53,6 +53,40 @@ def exec(command, args)
     expect(out).to eq("You gave me tacos, tofu, lasange")
   end
 
+  it "passes help flag to plugin" do
+    update_repo2 do
+      build_plugin "helpful" do |s|
+        s.write "plugins.rb", <<-RUBY
+          module Helpful
+            class Command
+              Bundler::Plugin::API.command "greet", self
+
+              def exec(command, args)
+                if args.include?("--help") || args.include?("-h")
+                  puts "Usage: bundle greet [NAME]"
+                else
+                  puts "Hello"
+                end
+              end
+            end
+          end
+        RUBY
+      end
+    end
+
+    bundle "plugin install helpful --source https://gem.repo2"
+    expect(out).to include("Installed plugin helpful")
+
+    bundle "greet --help"
+    expect(out).to eq("Usage: bundle greet [NAME]")
+
+    bundle "greet -h"
+    expect(out).to eq("Usage: bundle greet [NAME]")
+
+    bundle "help greet"
+    expect(out).to eq("Usage: bundle greet [NAME]")
+  end
+
   it "raises error on redeclaration of command" do
     update_repo2 do
       build_plugin "copycat" do |s|
diff --git a/spec/bundler/support/filters.rb b/spec/bundler/support/filters.rb
index 6e94b10e32c845..c6b60b5d52fe3a 100644
--- a/spec/bundler/support/filters.rb
+++ b/spec/bundler/support/filters.rb
@@ -29,6 +29,7 @@ def inspect
   config.filter_run_excluding jruby_only: RUBY_ENGINE != "jruby"
   config.filter_run_excluding truffleruby_only: RUBY_ENGINE != "truffleruby"
   config.filter_run_excluding man: Gem.win_platform?
+  config.filter_run_excluding mri_only: RUBY_ENGINE != "ruby"
 
   config.filter_run_when_matching :focus unless ENV["CI"]
 
diff --git a/test/ruby/test_iseq.rb b/test/ruby/test_iseq.rb
index fa716787fe9841..6846f7958b5a55 100644
--- a/test/ruby/test_iseq.rb
+++ b/test/ruby/test_iseq.rb
@@ -157,7 +157,7 @@ def (Object.new).touch(&) # :nodoc:
 
   def test_ractor_unshareable_outer_variable
     name = "\u{2603 26a1}"
-    assert_raise_with_message(ArgumentError, /\(#{name}\)/) do
+    assert_raise_with_message(Ractor::IsolationError, /\(#{name}\)/) do
       eval("#{name} = nil; Ractor.shareable_proc{#{name} = nil}")
     end
 
diff --git a/test/ruby/test_ractor.rb b/test/ruby/test_ractor.rb
index 6ae511217aca09..36467a35918981 100644
--- a/test/ruby/test_ractor.rb
+++ b/test/ruby/test_ractor.rb
@@ -213,6 +213,24 @@ def test_ifunc_proc_not_shareable
     assert_unshareable(pr, /not supported yet/, exception: RuntimeError)
   end
 
+  def test_ractor_new_raises_isolation_error_if_outer_variables_are_accessed
+    assert_raise(Ractor::IsolationError) do
+      channel = Ractor::Port.new
+      Ractor.new(channel) do
+        inbound_work = Ractor::Port.new
+        channel << inbound_work
+      end
+    end
+  end
+
+  def test_ractor_new_raises_isolation_error_if_proc_uses_yield
+    assert_raise(Ractor::IsolationError) do
+      Ractor.new do
+        yield
+      end
+    end
+  end
+
   def assert_make_shareable(obj)
     refute Ractor.shareable?(obj), "object was already shareable"
     Ractor.make_shareable(obj)
diff --git a/test/rubygems/test_gem_config_file.rb b/test/rubygems/test_gem_config_file.rb
index 79bf5f582c942c..6ed51f2704b8b6 100644
--- a/test/rubygems/test_gem_config_file.rb
+++ b/test/rubygems/test_gem_config_file.rb
@@ -43,6 +43,7 @@ def test_initialize
     assert_equal [@gem_repo], Gem.sources
     assert_equal 365, @cfg.cert_expiration_length_days
     assert_equal false, @cfg.ipv4_fallback_enabled
+    assert_equal false, @cfg.install_extension_in_lib
 
     File.open @temp_conf, "w" do |fp|
       fp.puts ":backtrace: true"
diff --git a/vm.c b/vm.c
index a9e952f705f131..a078f9e7344e4c 100644
--- a/vm.c
+++ b/vm.c
@@ -1521,10 +1521,10 @@ proc_shared_outer_variables(struct rb_id_table *outer_variables, bool isolate, c
         }
         if (*sep == ',') rb_str_cat_cstr(str, ")");
         rb_str_cat_cstr(str, data.yield ? " and uses 'yield'." : ".");
-        rb_exc_raise(rb_exc_new_str(rb_eArgError, str));
+        rb_exc_raise(rb_exc_new_str(rb_eRactorIsolationError, str));
     }
     else if (data.yield) {
-        rb_raise(rb_eArgError, "can not %s because it uses 'yield'.", message);
+        rb_raise(rb_eRactorIsolationError, "can not %s because it uses 'yield'.", message);
     }
 
     return data.read_only;