diff --git a/.github/release.yml b/.github/release.yml
new file mode 100644
index 0000000..db1d8e9
--- /dev/null
+++ b/.github/release.yml
@@ -0,0 +1,4 @@
+changelog:
+  exclude:
+    labels:
+      - dependencies # Added by Dependabot
diff --git a/.rubocop.yml b/.rubocop.yml
index 67680fa..4be2af1 100644
--- a/.rubocop.yml
+++ b/.rubocop.yml
@@ -9,6 +9,8 @@ AllCops:
     - pkg/**/*
     - tmp/**/*
     - bundler/tmp/**/*
+    - lib/compact_index.rb
+    - lib/compact_index/**/*
     - lib/rubygems/resolver/molinillo/**/*
     - lib/rubygems/tsort/**/*
     - lib/rubygems/optparse/**/*
diff --git a/Manifest.txt b/Manifest.txt
index d915241..39a745a 100644
--- a/Manifest.txt
+++ b/Manifest.txt
@@ -4,6 +4,11 @@ LICENSE.txt
 MIT.txt
 Manifest.txt
 README.md
+lib/compact_index.rb
+lib/compact_index/dependency.rb
+lib/compact_index/gem.rb
+lib/compact_index/gem_version.rb
+lib/compact_index/versions_file.rb
 lib/rubygems/commands/generate_index_command.rb
 lib/rubygems/indexer.rb
 lib/rubygems_plugin.rb
diff --git a/Rakefile b/Rakefile
index 86ad355..087ea7c 100644
--- a/Rakefile
+++ b/Rakefile
@@ -56,3 +56,29 @@ task :check_manifest do
     abort "Manifest is out of date. Run `rake update_manifest` to sync it"
   end
 end
+
+namespace :vendor do
+  desc "Sync vendored compact_index from rubygems/rubygems.org (REF=master)"
+  task :compact_index do
+    require "open-uri"
+    require "fileutils"
+
+    ref = ENV["REF"] || "master"
+    repo = "rubygems/rubygems.org"
+    paths = %w[
+      lib/compact_index.rb
+      lib/compact_index/dependency.rb
+      lib/compact_index/gem.rb
+      lib/compact_index/gem_version.rb
+      lib/compact_index/versions_file.rb
+    ]
+
+    paths.each do |path|
+      url = "https://raw.githubusercontent.com/#{repo}/#{ref}/#{path}"
+      puts "Fetching #{url}"
+      content = URI.parse(url).open(&:read)
+      FileUtils.mkdir_p(File.dirname(path))
+      File.write(path, content)
+    end
+  end
+end
diff --git a/lib/compact_index.rb b/lib/compact_index.rb
new file mode 100644
index 0000000..899c577
--- /dev/null
+++ b/lib/compact_index.rb
@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+# Vendored from https://github.com/rubygems/compact_index v0.15.0
+
+require_relative "compact_index/gem"
+require_relative "compact_index/gem_version"
+require_relative "compact_index/dependency"
+
+require_relative "compact_index/versions_file"
+
+module CompactIndex
+  def self.names(gem_names)
+    gem_names.join("\n").prepend("---\n") << "\n"
+  end
+
+  def self.versions(versions_file, gems = nil, args = {})
+    versions_file.contents(gems, args)
+  end
+
+  def self.info(versions)
+    versions.inject(+"---\n") do |output, version|
+      output << version.to_line << "\n"
+    end
+  end
+end
diff --git a/lib/compact_index/dependency.rb b/lib/compact_index/dependency.rb
new file mode 100644
index 0000000..bb3ba1b
--- /dev/null
+++ b/lib/compact_index/dependency.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module CompactIndex
+  Dependency = Struct.new(:gem, :version, :platform, :checksum) do
+    def version_and_platform
+      if platform.nil? || platform == "ruby"
+        version
+      else
+        "#{version}-#{platform}"
+      end
+    end
+  end
+end
diff --git a/lib/compact_index/gem.rb b/lib/compact_index/gem.rb
new file mode 100644
index 0000000..7358052
--- /dev/null
+++ b/lib/compact_index/gem.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module CompactIndex
+  Gem = Struct.new(:name, :versions) do
+    def <=>(other)
+      name <=> other.name
+    end
+  end
+end
diff --git a/lib/compact_index/gem_version.rb b/lib/compact_index/gem_version.rb
new file mode 100644
index 0000000..f083b3f
--- /dev/null
+++ b/lib/compact_index/gem_version.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+module CompactIndex
+  GemVersion = Struct.new(:number, :platform, :checksum, :info_checksum,
+                          :dependencies, :ruby_version, :rubygems_version) do
+    def number_and_platform
+      if platform.nil? || platform == "ruby"
+        number
+      else
+        "#{number}-#{platform}"
+      end
+    end
+
+    def <=>(other)
+      number_comp = number <=> other.number
+
+      if number_comp.zero?
+        [number, platform].compact <=> [other.number, other.platform].compact
+      else
+        number_comp
+      end
+    end
+
+    def to_line
+      line = "#{number_and_platform} #{deps_line}|checksum:#{checksum}"
+      line << ",ruby:#{ruby_version_line}" if ruby_version && ruby_version != ">= 0"
+      line << ",rubygems:#{rubygems_version_line}" if rubygems_version && rubygems_version != ">= 0"
+      line
+    end
+
+    private
+
+    def ruby_version_line
+      join_multiple(ruby_version)
+    end
+
+    def rubygems_version_line
+      join_multiple(rubygems_version)
+    end
+
+    def deps_line
+      return "" if dependencies.nil?
+
+      dependencies.map do |d|
+        [d[:gem], join_multiple(d.version_and_platform)].join(":")
+      end.join(",")
+    end
+
+    def join_multiple(requirements)
+      requirements = requirements.split(", ")
+      requirements.sort!
+      requirements.join("&")
+    end
+  end
+end
diff --git a/lib/compact_index/versions_file.rb b/lib/compact_index/versions_file.rb
new file mode 100644
index 0000000..77425c4
--- /dev/null
+++ b/lib/compact_index/versions_file.rb
@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+require "time"
+require "date"
+require "digest"
+
+module CompactIndex
+  class VersionsFile
+    def initialize(file = nil)
+      @path = file || "/versions.list"
+    end
+
+    def contents(gems = nil, args = {})
+      gems = calculate_info_checksums(gems) if args.delete(:calculate_info_checksums) { false }
+
+      raise ArgumentError, "Unknown options: #{args.keys.join(', ')}" unless args.empty?
+
+      File.read(@path).tap do |out|
+        out << gem_lines(gems) if gems
+      end
+    end
+
+    def updated_at
+      created_at_header(@path) || Time.at(0).utc.to_datetime
+    end
+
+    def create(gems, timestamp = Time.now.iso8601)
+      gems.sort!
+
+      File.open(@path, "w") do |io|
+        io.write "created_at: #{timestamp}\n---\n"
+        io.write gem_lines(gems)
+      end
+    end
+
+    private
+
+    def gem_lines(gems)
+      gems.reduce(+"") do |lines, gem|
+        version_numbers = gem.versions.map(&:number_and_platform).join(",")
+        lines << gem.name <<
+          " " << version_numbers <<
+          " #{gem.versions.last.info_checksum}\n"
+      end
+    end
+
+    def calculate_info_checksums(gems)
+      gems.each do |gem|
+        info_checksum = Digest::MD5.hexdigest(CompactIndex.info(gem[:versions]))
+        gem[:versions].last[:info_checksum] = info_checksum
+      end
+    end
+
+    def created_at_header(path)
+      return unless File.exist? path
+
+      File.open(path) do |file|
+        file.each_line do |line|
+          line.match(/created_at: (.*)\n|---\n/) do |match|
+            return match[1] && DateTime.parse(match[1])
+          end
+        end
+      end
+
+      nil
+    end
+  end
+end
diff --git a/lib/rubygems/indexer.rb b/lib/rubygems/indexer.rb
index dccaa58..4ff7c79 100644
--- a/lib/rubygems/indexer.rb
+++ b/lib/rubygems/indexer.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-require "compact_index"
+require_relative "../compact_index"
 require "rubygems"
 require "rubygems/package"
 require "tmpdir"
diff --git a/rubygems-generate_index.gemspec b/rubygems-generate_index.gemspec
index b5ceb5c..b9b0946 100644
--- a/rubygems-generate_index.gemspec
+++ b/rubygems-generate_index.gemspec
@@ -28,6 +28,4 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = Gem::Requirement.new(">= 3.0.0")
   s.required_rubygems_version = Gem::Requirement.new(">= 0")
-
-  s.add_dependency "compact_index", "~> 0.15.0"
 end