diff --git a/Gemfile b/Gemfile
index 5e46b7728..aed350593 100644
--- a/Gemfile
+++ b/Gemfile
@@ -19,6 +19,8 @@ gem "rom-sql", github: "rom-rb/rom-sql", branch: "master"
 gem "dry-monitor", github: "dry-rb/dry-monitor", branch: "master"
 gem "dry-events", github: "dry-rb/dry-events", branch: "master"
 
+gem "zeitwerk", github: "fxn/zeitwerk", branch: "main"
+
 group :sql do
   gem "jdbc-postgres", platforms: :jruby
   gem "jdbc-sqlite3", platforms: :jruby
diff --git a/Rakefile b/Rakefile
index 2cfddf2bd..705e07aab 100644
--- a/Rakefile
+++ b/Rakefile
@@ -5,7 +5,15 @@ require "bundler/gem_tasks"
 require "rspec/core"
 require "rspec/core/rake_task"
 
-RSpec::Core::RakeTask.new(:spec)
+RSpec::Core::RakeTask.new("spec:all") do |t|
+  t.pattern = ["spec/unit/**/*_spec.rb", "spec/integration/**/*_spec.rb"]
+end
+
+RSpec::Core::RakeTask.new("spec:compat") do |t|
+  t.pattern = ["spec/compat/**/*_spec.rb"]
+end
+
+task "spec" => ["spec:all", "spec:compat"]
 
 task default: :spec
 
@@ -25,8 +33,10 @@ namespace :benchmark do
   end
 end
 
+# rubocop:disable Lint/SuppressedException
 begin
   require "yard-junk/rake"
   YardJunk::Rake.define_task(:text)
 rescue LoadError
 end
+# rubocop:enable Lint/SuppressedException
diff --git a/docsite/core/source/framework-setup.html.md b/docsite/core/source/framework-setup.html.md
index 2bd180003..631a77727 100644
--- a/docsite/core/source/framework-setup.html.md
+++ b/docsite/core/source/framework-setup.html.md
@@ -65,7 +65,7 @@ module Persistence
 end
 
 configuration = ROM::Configuration.new(:memory)
-configuration.auto_registration('root_dir/lib/persistence/')
+configuration.auto_register('root_dir/lib/persistence/')
 container = ROM.container(configuration)
 ```
 
@@ -92,7 +92,7 @@ Notice that the directory structure is different from our module structure. Sinc
 
 ```ruby
 configuration = ROM::Configuration.new(:memory)
-configuration.auto_registration('/path/to/lib', namespace: 'Persistence')
+configuration.auto_register('/path/to/lib', namespace: 'Persistence')
 container = ROM.container(configuration)
 ```
 
@@ -146,7 +146,7 @@ end
 Then, auto-registration can be achieved with
 
 ```ruby
-configuration.auto_registration('/path/to/lib', namespace: 'MyApp::Persistence')
+configuration.auto_register('/path/to/lib', namespace: 'MyApp::Persistence')
 ```
 
 #### Turning namespace off
@@ -162,7 +162,7 @@ end
 
 ```ruby
 configuration = ROM::Configuration.new(:memory)
-configuration.auto_registration('/path/to/lib', namespace: false)
+configuration.auto_register('/path/to/lib', namespace: false)
 container = ROM.container(configuration)
 ```
 
diff --git a/lib/rom/compat.rb b/lib/rom/compat.rb
new file mode 100644
index 000000000..00e715e2f
--- /dev/null
+++ b/lib/rom/compat.rb
@@ -0,0 +1,3 @@
+# frozen_string_literal: true
+
+require_relative "compat/setup"
diff --git a/lib/rom/setup/auto_registration.rb b/lib/rom/compat/auto_registration.rb
similarity index 93%
rename from lib/rom/setup/auto_registration.rb
rename to lib/rom/compat/auto_registration.rb
index afbb82752..64b94b32f 100644
--- a/lib/rom/setup/auto_registration.rb
+++ b/lib/rom/compat/auto_registration.rb
@@ -6,9 +6,10 @@
 
 require "rom/types"
 require "rom/initializer"
-require "rom/setup/auto_registration_strategies/no_namespace"
-require "rom/setup/auto_registration_strategies/with_namespace"
-require "rom/setup/auto_registration_strategies/custom_namespace"
+
+require_relative "auto_registration_strategies/no_namespace"
+require_relative "auto_registration_strategies/with_namespace"
+require_relative "auto_registration_strategies/custom_namespace"
 
 module ROM
   # AutoRegistration is used to load component files automatically from the provided directory path
diff --git a/lib/rom/setup/auto_registration_strategies/base.rb b/lib/rom/compat/auto_registration_strategies/base.rb
similarity index 100%
rename from lib/rom/setup/auto_registration_strategies/base.rb
rename to lib/rom/compat/auto_registration_strategies/base.rb
diff --git a/lib/rom/setup/auto_registration_strategies/custom_namespace.rb b/lib/rom/compat/auto_registration_strategies/custom_namespace.rb
similarity index 97%
rename from lib/rom/setup/auto_registration_strategies/custom_namespace.rb
rename to lib/rom/compat/auto_registration_strategies/custom_namespace.rb
index 58fea65d0..8882fd9fc 100644
--- a/lib/rom/setup/auto_registration_strategies/custom_namespace.rb
+++ b/lib/rom/compat/auto_registration_strategies/custom_namespace.rb
@@ -4,7 +4,8 @@
 
 require "rom/support/inflector"
 require "rom/types"
-require "rom/setup/auto_registration_strategies/base"
+
+require_relative "base"
 
 module ROM
   module AutoRegistrationStrategies
diff --git a/lib/rom/setup/auto_registration_strategies/no_namespace.rb b/lib/rom/compat/auto_registration_strategies/no_namespace.rb
similarity index 93%
rename from lib/rom/setup/auto_registration_strategies/no_namespace.rb
rename to lib/rom/compat/auto_registration_strategies/no_namespace.rb
index a535b42f8..849f95d85 100644
--- a/lib/rom/setup/auto_registration_strategies/no_namespace.rb
+++ b/lib/rom/compat/auto_registration_strategies/no_namespace.rb
@@ -4,7 +4,7 @@
 
 require "rom/support/inflector"
 require "rom/types"
-require "rom/setup/auto_registration_strategies/base"
+require_relative "base"
 
 module ROM
   module AutoRegistrationStrategies
diff --git a/lib/rom/setup/auto_registration_strategies/with_namespace.rb b/lib/rom/compat/auto_registration_strategies/with_namespace.rb
similarity index 92%
rename from lib/rom/setup/auto_registration_strategies/with_namespace.rb
rename to lib/rom/compat/auto_registration_strategies/with_namespace.rb
index 1b113fffa..d5cad81a1 100644
--- a/lib/rom/setup/auto_registration_strategies/with_namespace.rb
+++ b/lib/rom/compat/auto_registration_strategies/with_namespace.rb
@@ -3,7 +3,7 @@
 require "pathname"
 
 require "rom/support/inflector"
-require "rom/setup/auto_registration_strategies/base"
+require_relative "base"
 
 module ROM
   module AutoRegistrationStrategies
diff --git a/lib/rom/compat/setup.rb b/lib/rom/compat/setup.rb
new file mode 100644
index 000000000..eb754747b
--- /dev/null
+++ b/lib/rom/compat/setup.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+require_relative "auto_registration"
+
+module ROM
+  # Setup objects collect component classes during setup/finalization process
+  #
+  # @api public
+  class Setup
+    # Enable auto-registration for a given setup object
+    #
+    # @param [String, Pathname] directory The root path to components
+    # @param [Hash] options
+    # @option options [Boolean, String] :namespace Toggle root namespace
+    #                                              or provide a custom namespace name
+    #
+    # @return [Setup]
+    #
+    # @deprecated
+    #
+    # @api public
+    def auto_registration(directory, **options)
+      auto_registration = AutoRegistration.new(directory, inflector: inflector, **options)
+      auto_registration.relations.map { |r| register_relation(r) }
+      auto_registration.commands.map { |r| register_command(r) }
+      auto_registration.mappers.map { |r| register_mapper(r) }
+      self
+    end
+  end
+end
diff --git a/lib/rom/container.rb b/lib/rom/container.rb
index dd1d37c6a..bc4eff800 100644
--- a/lib/rom/container.rb
+++ b/lib/rom/container.rb
@@ -74,7 +74,7 @@ module ROM
   #
   # @example multi-step setup with auto-registration
   #   config = ROM::Configuration.new(:sql, 'sqlite::memory')
-  #   config.auto_registration('./persistence', namespace: false)
+  #   config.auto_register('./persistence', namespace: false)
   #
   #   config.default.create_table :users do
   #     primary_key :id
diff --git a/lib/rom/loader.rb b/lib/rom/loader.rb
new file mode 100644
index 000000000..bf1f22889
--- /dev/null
+++ b/lib/rom/loader.rb
@@ -0,0 +1,151 @@
+# frozen_string_literal: true
+
+require "pathname"
+require "zeitwerk"
+
+require "rom/support/inflector"
+
+require "rom/types"
+require "rom/initializer"
+require "rom/loader"
+
+module ROM
+  # AutoRegistration is used to load component files automatically from the provided directory path
+  #
+  # @api public
+  class Loader
+    extend Initializer
+
+    NamespaceType = Types::Strict::Bool | Types.Instance(Module)
+
+    PathnameType = Types.Constructor(Pathname, &Kernel.method(:Pathname))
+
+    InflectorType = Types.Interface(:camelize)
+
+    ComponentDirs = Types::Strict::Hash.constructor { |hash| hash.transform_values(&:to_s) }
+
+    DEFAULT_MAPPING = {
+      relations: "relations",
+      mappers: "mappers",
+      commands: "commands"
+    }.freeze
+
+    # @!attribute [r] directory
+    #   @return [Pathname] The root path
+    param :root_directory, type: PathnameType
+
+    # @!attribute [r] namespace
+    #   @return [Boolean,String]
+    #     The name of the top level namespace or true/false which
+    #     enables/disables default top level namespace inferred from the dir name
+    option :namespace, type: NamespaceType, default: -> { true }
+
+    # @!attribute [r] component_dirs
+    #   @return [Hash] component => dir-name map
+    option :component_dirs, type: ComponentDirs, default: -> { DEFAULT_MAPPING }
+
+    # @!attribute [r] inflector
+    #   @return [Dry::Inflector] String inflector
+    #   @api private
+    option :inflector, type: InflectorType, default: -> { Inflector }
+
+    # @!attribute [r] loaded_constants
+    #   @return [Dry::Inflector] String inflector
+    #   @api private
+    option :inflector, type: InflectorType, default: -> { Inflector }
+
+    option :loaded_constants, default: -> { {relations: [], commands: [], mappers: []} }
+
+    # Load components
+    #
+    # @api private
+    def constants(component_type)
+      unless @loaded
+        setup and backend.eager_load
+        @loaded = true
+      end
+
+      loaded_constants.fetch(component_type)
+    end
+
+    # Load relation files
+    #
+    # @api private
+    def relations
+      constants(__method__)
+    end
+
+    # Load command files
+    #
+    # @api private
+    def commands
+      constants(__method__)
+    end
+
+    # Load mapper files
+    #
+    # @api private
+    def mappers
+      constants(__method__)
+    end
+
+    private
+
+    # @api private
+    def backend
+      @backend ||= Zeitwerk::Loader.new
+    end
+
+    # @api private
+    # rubocop:disable Metrics/AbcSize
+    def setup
+      backend.inflector = inflector
+
+      case namespace
+      when true
+        backend.push_dir(root_directory.join("..").realpath)
+
+        component_dirs.each_value do |dir|
+          backend.collapse(root_directory.join(dir).join("**/*"))
+        end
+      when false
+        backend.push_dir(root_directory)
+      else
+        backend.push_dir(root_directory, namespace: namespace)
+      end
+
+      excluded_dirs.each do |dir|
+        backend.ignore(dir)
+      end
+
+      backend.on_load do |_, const, path|
+        if (type = path_to_component_type(path))
+          loaded_constants[type] << const
+        end
+      end
+
+      backend.setup
+    end
+    # rubocop:enable Metrics/AbcSize
+
+    # @api private
+    def path_to_component_type(path)
+      return unless File.file?(path)
+
+      component_dirs
+        .detect { |_, dir|
+          path.start_with?(root_directory.join(dir).to_s)
+        }
+        &.first
+    end
+
+    # @api private
+    def excluded_dirs
+      root_directory
+        .children
+        .select(&:directory?)
+        .reject { |dir| component_dirs.values.include?(dir.basename.to_s) }
+        .map { |name| root_directory.join(name) }
+    end
+  end
+end
diff --git a/lib/rom/setup.rb b/lib/rom/setup.rb
index 5d2507979..ec9ff7ea8 100644
--- a/lib/rom/setup.rb
+++ b/lib/rom/setup.rb
@@ -1,27 +1,12 @@
 # frozen_string_literal: true
 
-require "rom/setup/auto_registration"
+require "rom/loader"
 
 module ROM
   # Setup objects collect component classes during setup/finalization process
   #
   # @api public
   class Setup
-    # @return [Array] registered relation subclasses
-    #
-    # @api private
-    attr_reader :relation_classes
-
-    # @return [Array] registered mapper subclasses
-    #
-    # @api private
-    attr_reader :mapper_classes
-
-    # @return [Array] registered command subclasses
-    #
-    # @api private
-    attr_reader :command_classes
-
     # @api private
     attr_reader :plugins
 
@@ -31,57 +16,76 @@ class Setup
     # @api private
     attr_accessor :inflector
 
+    # @api private
+    attr_reader :components
+
     # @api private
     def initialize(notifications)
-      @relation_classes = []
-      @command_classes = []
-      @mapper_classes = []
       @plugins = []
       @notifications = notifications
       @inflector = Inflector
+      @components = {relations: [], commands: [], mappers: []}
     end
 
     # Enable auto-registration for a given setup object
     #
     # @param [String, Pathname] directory The root path to components
     # @param [Hash] options
-    # @option options [Boolean, String] :namespace Enable/disable namespace or provide a custom namespace name
+    # @option options [Boolean] :namespace Toggle root namespace
     #
     # @return [Setup]
     #
     # @api public
-    def auto_registration(directory, **options)
-      auto_registration = AutoRegistration.new(directory, inflector: inflector, **options)
-      auto_registration.relations.map { |r| register_relation(r) }
-      auto_registration.commands.map { |r| register_command(r) }
-      auto_registration.mappers.map { |r| register_mapper(r) }
-      self
+    def auto_register(directory, **options)
+      @auto_register ||= [directory, {**options}]
     end
 
     # Relation sub-classes are being registered with this method during setup
     #
     # @api private
     def register_relation(*klasses)
-      @relation_classes.concat(klasses)
+      components[:relations].concat(klasses)
     end
 
     # Mapper sub-classes are being registered with this method during setup
     #
     # @api private
     def register_mapper(*klasses)
-      @mapper_classes.concat(klasses)
+      components[:mappers].concat(klasses)
     end
 
     # Command sub-classes are being registered with this method during setup
     #
     # @api private
     def register_command(*klasses)
-      @command_classes.concat(klasses)
+      components[:commands].concat(klasses)
+    end
+
+    # @api private
+    def relation_classes
+      @relation_classes ||= components[:relations].concat(loader&.relations || [])
+    end
+
+    # @api private
+    def command_classes
+      @command_classes ||= components[:commands].concat(loader&.commands || [])
+    end
+
+    # @api private
+    def mapper_classes
+      @mapper_classes ||= components[:mappers].concat(loader&.mappers || [])
     end
 
     # @api private
     def register_plugin(plugin)
       plugins << plugin
     end
+
+    private
+
+    # @api private
+    def loader
+      @loader ||= Loader.new(@auto_register[0], **(@auto_register[1] || {})) if @auto_register
+    end
   end
 end
diff --git a/lib/rom/support/inflector.rb b/lib/rom/support/inflector.rb
index 84576219f..6fa93e74e 100644
--- a/lib/rom/support/inflector.rb
+++ b/lib/rom/support/inflector.rb
@@ -3,7 +3,15 @@
 require "dry/inflector"
 
 module ROM
+  module ZeitwerkCompatibility
+    def camelize(name, *)
+      super(name)
+    end
+  end
+
   Inflector = Dry::Inflector.new do |i|
     i.plural(/people\z/i, "people")
   end
+
+  Inflector.extend(ZeitwerkCompatibility)
 end
diff --git a/rom.gemspec b/rom.gemspec
index 5b05a2962..24394cd3a 100644
--- a/rom.gemspec
+++ b/rom.gemspec
@@ -20,6 +20,7 @@ Gem::Specification.new do |gem|
   gem.required_ruby_version = '>= 2.4.0'
 
   gem.add_runtime_dependency 'concurrent-ruby', '~> 1.1'
+  gem.add_runtime_dependency 'zeitwerk'
   gem.add_runtime_dependency 'dry-core', '~> 0.6', '>= 0.6'
   gem.add_runtime_dependency 'dry-inflector', '~> 0.1'
   gem.add_runtime_dependency 'dry-container', '~> 0.7'
diff --git a/spec/fixtures/app/commands/create_user.rb b/spec/compat/fixtures/app/commands/create_user.rb
similarity index 100%
rename from spec/fixtures/app/commands/create_user.rb
rename to spec/compat/fixtures/app/commands/create_user.rb
diff --git a/spec/fixtures/app/mappers/user_list.rb b/spec/compat/fixtures/app/mappers/user_list.rb
similarity index 100%
rename from spec/fixtures/app/mappers/user_list.rb
rename to spec/compat/fixtures/app/mappers/user_list.rb
diff --git a/spec/fixtures/app/my_commands/create_user.rb b/spec/compat/fixtures/app/my_commands/create_user.rb
similarity index 100%
rename from spec/fixtures/app/my_commands/create_user.rb
rename to spec/compat/fixtures/app/my_commands/create_user.rb
diff --git a/spec/fixtures/app/my_mappers/user_list.rb b/spec/compat/fixtures/app/my_mappers/user_list.rb
similarity index 100%
rename from spec/fixtures/app/my_mappers/user_list.rb
rename to spec/compat/fixtures/app/my_mappers/user_list.rb
diff --git a/spec/fixtures/app/my_relations/users.rb b/spec/compat/fixtures/app/my_relations/users.rb
similarity index 100%
rename from spec/fixtures/app/my_relations/users.rb
rename to spec/compat/fixtures/app/my_relations/users.rb
diff --git a/spec/fixtures/app/relations/users.rb b/spec/compat/fixtures/app/relations/users.rb
similarity index 100%
rename from spec/fixtures/app/relations/users.rb
rename to spec/compat/fixtures/app/relations/users.rb
diff --git a/spec/fixtures/custom/commands/create_user.rb b/spec/compat/fixtures/custom/commands/create_user.rb
similarity index 100%
rename from spec/fixtures/custom/commands/create_user.rb
rename to spec/compat/fixtures/custom/commands/create_user.rb
diff --git a/spec/fixtures/custom/mappers/user_list.rb b/spec/compat/fixtures/custom/mappers/user_list.rb
similarity index 100%
rename from spec/fixtures/custom/mappers/user_list.rb
rename to spec/compat/fixtures/custom/mappers/user_list.rb
diff --git a/spec/fixtures/custom/relations/users.rb b/spec/compat/fixtures/custom/relations/users.rb
similarity index 100%
rename from spec/fixtures/custom/relations/users.rb
rename to spec/compat/fixtures/custom/relations/users.rb
diff --git a/spec/fixtures/custom_namespace/commands/create_customer.rb b/spec/compat/fixtures/custom_namespace/commands/create_customer.rb
similarity index 100%
rename from spec/fixtures/custom_namespace/commands/create_customer.rb
rename to spec/compat/fixtures/custom_namespace/commands/create_customer.rb
diff --git a/spec/fixtures/custom_namespace/mappers/customer_list.rb b/spec/compat/fixtures/custom_namespace/mappers/customer_list.rb
similarity index 100%
rename from spec/fixtures/custom_namespace/mappers/customer_list.rb
rename to spec/compat/fixtures/custom_namespace/mappers/customer_list.rb
diff --git a/spec/fixtures/custom_namespace/relations/customers.rb b/spec/compat/fixtures/custom_namespace/relations/customers.rb
similarity index 100%
rename from spec/fixtures/custom_namespace/relations/customers.rb
rename to spec/compat/fixtures/custom_namespace/relations/customers.rb
diff --git a/spec/compat/fixtures/lib/persistence/commands/create_user.rb b/spec/compat/fixtures/lib/persistence/commands/create_user.rb
new file mode 100644
index 000000000..e4032edf0
--- /dev/null
+++ b/spec/compat/fixtures/lib/persistence/commands/create_user.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Persistence
+  module Commands
+    class CreateUser
+    end
+  end
+end
diff --git a/spec/compat/fixtures/lib/persistence/mappers/user_list.rb b/spec/compat/fixtures/lib/persistence/mappers/user_list.rb
new file mode 100644
index 000000000..19f231b4d
--- /dev/null
+++ b/spec/compat/fixtures/lib/persistence/mappers/user_list.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Persistence
+  module Mappers
+    class UserList
+    end
+  end
+end
diff --git a/spec/compat/fixtures/lib/persistence/my_commands/create_user.rb b/spec/compat/fixtures/lib/persistence/my_commands/create_user.rb
new file mode 100644
index 000000000..01d8f3395
--- /dev/null
+++ b/spec/compat/fixtures/lib/persistence/my_commands/create_user.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Persistence
+  module MyCommands
+    class CreateUser
+    end
+  end
+end
diff --git a/spec/compat/fixtures/lib/persistence/my_mappers/user_list.rb b/spec/compat/fixtures/lib/persistence/my_mappers/user_list.rb
new file mode 100644
index 000000000..cea9458a1
--- /dev/null
+++ b/spec/compat/fixtures/lib/persistence/my_mappers/user_list.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Persistence
+  module MyMappers
+    class UserList
+    end
+  end
+end
diff --git a/spec/compat/fixtures/lib/persistence/my_relations/users.rb b/spec/compat/fixtures/lib/persistence/my_relations/users.rb
new file mode 100644
index 000000000..871e8a295
--- /dev/null
+++ b/spec/compat/fixtures/lib/persistence/my_relations/users.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Persistence
+  module MyRelations
+    class Users
+    end
+  end
+end
diff --git a/spec/compat/fixtures/lib/persistence/relations/users.rb b/spec/compat/fixtures/lib/persistence/relations/users.rb
new file mode 100644
index 000000000..9b03279d9
--- /dev/null
+++ b/spec/compat/fixtures/lib/persistence/relations/users.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Persistence
+  module Relations
+    class Users
+    end
+  end
+end
diff --git a/spec/compat/fixtures/wrong/commands/create_customer.rb b/spec/compat/fixtures/wrong/commands/create_customer.rb
new file mode 100644
index 000000000..f4c4fe23d
--- /dev/null
+++ b/spec/compat/fixtures/wrong/commands/create_customer.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+module My
+  module NewNamespace
+    module Foo
+      class CreateCustomer
+      end
+    end
+  end
+end
diff --git a/spec/compat/fixtures/wrong/mappers/customer_list.rb b/spec/compat/fixtures/wrong/mappers/customer_list.rb
new file mode 100644
index 000000000..2f7aa5e15
--- /dev/null
+++ b/spec/compat/fixtures/wrong/mappers/customer_list.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+module My
+  module NewNamespace
+    module Foo
+      class CustomerList
+      end
+    end
+  end
+end
diff --git a/spec/compat/fixtures/wrong/relations/customers.rb b/spec/compat/fixtures/wrong/relations/customers.rb
new file mode 100644
index 000000000..a91b85cb8
--- /dev/null
+++ b/spec/compat/fixtures/wrong/relations/customers.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+module My
+  module NewNamespace
+    module Foo
+      class Customers
+      end
+    end
+  end
+end
diff --git a/spec/fixtures/xml_space/xml_commands/create_customer.rb b/spec/compat/fixtures/xml_space/xml_commands/create_customer.rb
similarity index 100%
rename from spec/fixtures/xml_space/xml_commands/create_customer.rb
rename to spec/compat/fixtures/xml_space/xml_commands/create_customer.rb
diff --git a/spec/fixtures/xml_space/xml_mappers/customer_list.rb b/spec/compat/fixtures/xml_space/xml_mappers/customer_list.rb
similarity index 100%
rename from spec/fixtures/xml_space/xml_mappers/customer_list.rb
rename to spec/compat/fixtures/xml_space/xml_mappers/customer_list.rb
diff --git a/spec/fixtures/xml_space/xml_relations/customers.rb b/spec/compat/fixtures/xml_space/xml_relations/customers.rb
similarity index 100%
rename from spec/fixtures/xml_space/xml_relations/customers.rb
rename to spec/compat/fixtures/xml_space/xml_relations/customers.rb
diff --git a/spec/unit/rom/setup/auto_registration_spec.rb b/spec/compat/unit/setup/auto_registration_spec.rb
similarity index 93%
rename from spec/unit/rom/setup/auto_registration_spec.rb
rename to spec/compat/unit/setup/auto_registration_spec.rb
index 00fb85fe9..cad579889 100644
--- a/spec/unit/rom/setup/auto_registration_spec.rb
+++ b/spec/compat/unit/setup/auto_registration_spec.rb
@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
-require "rom/setup"
-require "rom/support/notifications"
+require "rom/compat"
 
 RSpec.describe ROM::Setup, "#auto_registration" do
   let!(:loaded_features) { $LOADED_FEATURES.dup }
@@ -21,7 +20,7 @@
   context "with default component_dirs" do
     context "with namespace turned on" do
       before do
-        setup.auto_registration(SPEC_ROOT.join("fixtures/lib/persistence").to_s)
+        setup.auto_registration(SPEC_ROOT.join("compat/fixtures/lib/persistence").to_s)
       end
 
       describe "#relations" do
@@ -45,7 +44,7 @@
 
     context "with namespace turned off" do
       before do
-        setup.auto_registration(SPEC_ROOT.join("fixtures/app"), namespace: false)
+        setup.auto_registration(SPEC_ROOT.join("compat/fixtures/app"), namespace: false)
       end
 
       describe "#relations" do
@@ -72,7 +71,7 @@
     context "with namespace turned on" do
       before do
         setup.auto_registration(
-          SPEC_ROOT.join("fixtures/lib/persistence").to_s,
+          SPEC_ROOT.join("compat/fixtures/lib/persistence").to_s,
           component_dirs: {
             relations: :my_relations,
             mappers: :my_mappers,
@@ -103,7 +102,7 @@
     context "with namespace turned off" do
       before do
         setup.auto_registration(
-          SPEC_ROOT.join("fixtures/app"),
+          SPEC_ROOT.join("compat/fixtures/app"),
           component_dirs: {
             relations: :my_relations,
             mappers: :my_mappers,
@@ -136,7 +135,7 @@
       context "when namespace has subnamespace" do
         before do
           setup.auto_registration(
-            SPEC_ROOT.join("fixtures/custom_namespace"),
+            SPEC_ROOT.join("compat/fixtures/custom_namespace"),
             component_dirs: {
               relations: :relations,
               mappers: :mappers,
@@ -183,7 +182,7 @@ module Customers
       context "when namespace has wrong subnamespace" do
         subject(:registration) do
           setup.auto_registration(
-            SPEC_ROOT.join("fixtures/wrong"),
+            SPEC_ROOT.join("compat/fixtures/wrong"),
             component_dirs: {
               relations: :relations,
               mappers: :mappers,
@@ -209,7 +208,7 @@ module Customers
       context "when namespace does not implement subnamespace" do
         before do
           setup.auto_registration(
-            SPEC_ROOT.join("fixtures/custom"),
+            SPEC_ROOT.join("compat/fixtures/custom"),
             component_dirs: {
               relations: :relations,
               mappers: :mappers,
@@ -248,7 +247,7 @@ module Customers
         before do
           setup.inflector = inflector
           setup.auto_registration(
-            SPEC_ROOT.join("fixtures/xml_space"),
+            SPEC_ROOT.join("compat/fixtures/xml_space"),
             component_dirs: {
               relations: :xml_relations,
               mappers: :xml_mappers,
diff --git a/spec/fixtures/app/persistence/commands/create_user.rb b/spec/fixtures/app/persistence/commands/create_user.rb
new file mode 100644
index 000000000..6eb0abc6c
--- /dev/null
+++ b/spec/fixtures/app/persistence/commands/create_user.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+module Commands
+  class CreateUser
+  end
+end
diff --git a/spec/fixtures/app/persistence/mappers/user_list.rb b/spec/fixtures/app/persistence/mappers/user_list.rb
new file mode 100644
index 000000000..f6fc2b677
--- /dev/null
+++ b/spec/fixtures/app/persistence/mappers/user_list.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+module Mappers
+  class UserList
+  end
+end
diff --git a/spec/fixtures/app/persistence/my_commands/create_user.rb b/spec/fixtures/app/persistence/my_commands/create_user.rb
new file mode 100644
index 000000000..a324a7271
--- /dev/null
+++ b/spec/fixtures/app/persistence/my_commands/create_user.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+module MyCommands
+  class CreateUser
+  end
+end
diff --git a/spec/fixtures/app/persistence/my_mappers/user_list.rb b/spec/fixtures/app/persistence/my_mappers/user_list.rb
new file mode 100644
index 000000000..8795e40a9
--- /dev/null
+++ b/spec/fixtures/app/persistence/my_mappers/user_list.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+module MyMappers
+  class UserList
+  end
+end
diff --git a/spec/fixtures/app/persistence/my_relations/users.rb b/spec/fixtures/app/persistence/my_relations/users.rb
new file mode 100644
index 000000000..247d3dc84
--- /dev/null
+++ b/spec/fixtures/app/persistence/my_relations/users.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+module MyRelations
+  class Users
+  end
+end
diff --git a/spec/fixtures/app/persistence/relations/users.rb b/spec/fixtures/app/persistence/relations/users.rb
new file mode 100644
index 000000000..6a0fbf2d3
--- /dev/null
+++ b/spec/fixtures/app/persistence/relations/users.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+module Relations
+  class Users
+  end
+end
diff --git a/spec/fixtures/custom/xml_space/xml_commands/create_customer.rb b/spec/fixtures/custom/xml_space/xml_commands/create_customer.rb
new file mode 100644
index 000000000..c5d2cd8b7
--- /dev/null
+++ b/spec/fixtures/custom/xml_space/xml_commands/create_customer.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module XMLSpace
+  module XMLCommands
+    class CreateCustomer
+    end
+  end
+end
diff --git a/spec/fixtures/custom/xml_space/xml_mappers/customer_list.rb b/spec/fixtures/custom/xml_space/xml_mappers/customer_list.rb
new file mode 100644
index 000000000..097965922
--- /dev/null
+++ b/spec/fixtures/custom/xml_space/xml_mappers/customer_list.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module XMLSpace
+  module XMLMappers
+    class CustomerList
+    end
+  end
+end
diff --git a/spec/fixtures/custom/xml_space/xml_relations/customers.rb b/spec/fixtures/custom/xml_space/xml_relations/customers.rb
new file mode 100644
index 000000000..29c01893a
--- /dev/null
+++ b/spec/fixtures/custom/xml_space/xml_relations/customers.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module XMLSpace
+  module XMLRelations
+    class Customers
+    end
+  end
+end
diff --git a/spec/fixtures/explicit/commands/create_user.rb b/spec/fixtures/explicit/commands/create_user.rb
new file mode 100644
index 000000000..e8c720a83
--- /dev/null
+++ b/spec/fixtures/explicit/commands/create_user.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Test
+  module Commands
+    class CreateUser
+    end
+  end
+end
diff --git a/spec/fixtures/explicit/mappers/user_list.rb b/spec/fixtures/explicit/mappers/user_list.rb
new file mode 100644
index 000000000..732ae296e
--- /dev/null
+++ b/spec/fixtures/explicit/mappers/user_list.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Test
+  module Mappers
+    class UserList
+    end
+  end
+end
diff --git a/spec/fixtures/explicit/relations/users.rb b/spec/fixtures/explicit/relations/users.rb
new file mode 100644
index 000000000..4d82cb2c7
--- /dev/null
+++ b/spec/fixtures/explicit/relations/users.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Test
+  module Relations
+    class Users
+    end
+  end
+end
diff --git a/spec/fixtures/explicit_custom/my_commands/create_user.rb b/spec/fixtures/explicit_custom/my_commands/create_user.rb
new file mode 100644
index 000000000..1eec6974e
--- /dev/null
+++ b/spec/fixtures/explicit_custom/my_commands/create_user.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Test
+  module MyCommands
+    class CreateUser
+    end
+  end
+end
diff --git a/spec/fixtures/explicit_custom/my_mappers/user_list.rb b/spec/fixtures/explicit_custom/my_mappers/user_list.rb
new file mode 100644
index 000000000..7bf348a84
--- /dev/null
+++ b/spec/fixtures/explicit_custom/my_mappers/user_list.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Test
+  module MyMappers
+    class UserList
+    end
+  end
+end
diff --git a/spec/fixtures/explicit_custom/my_relations/users.rb b/spec/fixtures/explicit_custom/my_relations/users.rb
new file mode 100644
index 000000000..9f186b451
--- /dev/null
+++ b/spec/fixtures/explicit_custom/my_relations/users.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Test
+  module MyRelations
+    class Users
+    end
+  end
+end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 8d1245ed8..f5d7f89f3 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -8,6 +8,8 @@
 
 require "warning"
 
+Warning.ignore(/zeitwerk/)
+Warning.ignore(/pry-byebug/)
 Warning.ignore(/sequel/)
 Warning.ignore(/mysql2/)
 Warning.ignore(/rspec-core/)
@@ -21,18 +23,20 @@
 require "rom/core"
 require "rom-changeset"
 
-Dir[root.join("support/**/*.rb").to_s].each do |f|
+Dir[root.join("support/**/*.rb").to_s].sort.each do |f|
   require f unless f.include?("coverage")
 end
 
-Dir[root.join("shared/**/*.rb").to_s].each do |f|
+Dir[root.join("shared/**/*.rb").to_s].sort.each do |f|
   require f
 end
 
+# rubocop:disable Lint/SuppressedException
 begin
   require "pry-byebug"
 rescue LoadError
 end
+# rubocop:enable Lint/SuppressedException
 
 module SpecProfiler
   def report(*)
diff --git a/spec/unit/rom/setup/auto_register_spec.rb b/spec/unit/rom/setup/auto_register_spec.rb
new file mode 100644
index 000000000..740c4bea5
--- /dev/null
+++ b/spec/unit/rom/setup/auto_register_spec.rb
@@ -0,0 +1,133 @@
+# frozen_string_literal: true
+
+require "rom/setup"
+require "rom/support/notifications"
+
+RSpec.describe ROM::Setup, "#auto_register" do
+  subject(:setup) { ROM::Setup.new(notifications) }
+
+  let(:notifications) { instance_double(ROM::Notifications::EventBus) }
+
+  around do |example|
+    example.run
+  ensure
+    zeitwerk_teardown
+  end
+
+  def zeitwerk_teardown
+    Zeitwerk::Registry.loaders.each(&:unload)
+    Zeitwerk::Registry.loaders.clear
+    Zeitwerk::Registry.loaders_managing_gems.clear
+    Zeitwerk::ExplicitNamespace.cpaths.clear
+    Zeitwerk::ExplicitNamespace.tracer.disable
+  end
+
+  context "with default component dirs and namespace turned on" do
+    it "loads files and returns constants" do
+      setup.auto_register(SPEC_ROOT.join("fixtures/lib/persistence"))
+
+      expect(setup.relation_classes).to eql([Persistence::Relations::Users])
+      expect(setup.command_classes).to eql([Persistence::Commands::CreateUser])
+      expect(setup.mapper_classes).to eql([Persistence::Mappers::UserList])
+    end
+  end
+
+  context "with custom component dirs and namespace turned on" do
+    it "loads files and returns constants" do
+      setup.auto_register(
+        SPEC_ROOT.join("fixtures/lib/persistence"),
+        component_dirs: {
+          relations: :my_relations,
+          mappers: :my_mappers,
+          commands: :my_commands
+        }
+      )
+
+      expect(setup.relation_classes).to eql([Persistence::MyRelations::Users])
+      expect(setup.command_classes).to eql([Persistence::MyCommands::CreateUser])
+      expect(setup.mapper_classes).to eql([Persistence::MyMappers::UserList])
+    end
+  end
+
+  context "with default component dirs and namespace set explicitly" do
+    it "loads files and returns constants" do
+      setup.auto_register(SPEC_ROOT.join("fixtures/explicit"), namespace: Test)
+
+      expect(setup.relation_classes).to eql([Test::Relations::Users])
+      expect(setup.command_classes).to eql([Test::Commands::CreateUser])
+      expect(setup.mapper_classes).to eql([Test::Mappers::UserList])
+    end
+  end
+
+  context "with custom component dirs and namespace set explicitly" do
+    it "loads files and returns constants" do
+      setup.auto_register(
+        SPEC_ROOT.join("fixtures/explicit_custom"),
+        component_dirs: {
+          relations: :my_relations,
+          mappers: :my_mappers,
+          commands: :my_commands
+        },
+        namespace: Test
+      )
+
+      expect(setup.relation_classes).to eql([Test::MyRelations::Users])
+      expect(setup.command_classes).to eql([Test::MyCommands::CreateUser])
+      expect(setup.mapper_classes).to eql([Test::MyMappers::UserList])
+    end
+  end
+
+  context "with default component dirs and namespace turned off" do
+    it "loads files and returns constants" do
+      setup.auto_register(SPEC_ROOT.join("fixtures/app/persistence"), namespace: false)
+
+      expect(setup.relation_classes).to eql([Relations::Users])
+      expect(setup.command_classes).to eql([Commands::CreateUser])
+      expect(setup.mapper_classes).to eql([Mappers::UserList])
+    end
+  end
+
+  context "with custom component dirs and namespace turned off" do
+    it "loads files and returns constants" do
+      setup.auto_register(
+        SPEC_ROOT.join("fixtures/app/persistence"),
+        component_dirs: {
+          relations: :my_relations,
+          mappers: :my_mappers,
+          commands: :my_commands
+        },
+        namespace: false
+      )
+
+      expect(setup.relation_classes).to eql([MyRelations::Users])
+      expect(setup.command_classes).to eql([MyCommands::CreateUser])
+      expect(setup.mapper_classes).to eql([MyMappers::UserList])
+    end
+  end
+
+  context "with custom component dirs and a customized inflector" do
+    let(:inflector) do
+      Dry::Inflector.new do |i|
+        i.acronym("XML")
+      end
+    end
+
+    it "loads files and returns constants" do
+      inflector.extend(ROM::ZeitwerkCompatibility)
+
+      setup.auto_register(
+        SPEC_ROOT.join("fixtures/custom/xml_space"),
+        inflector: inflector,
+        component_dirs: {
+          relations: :xml_relations,
+          mappers: :xml_mappers,
+          commands: :xml_commands
+        }
+      )
+
+      expect(setup.relation_classes).to eql([XMLSpace::XMLRelations::Customers])
+      expect(setup.command_classes).to eql([XMLSpace::XMLCommands::CreateCustomer])
+      expect(setup.mapper_classes).to eql([XMLSpace::XMLMappers::CustomerList])
+    end
+  end
+end