diff --git a/actionmailer/lib/action_mailer/railtie.rb b/actionmailer/lib/action_mailer/railtie.rb
index 76c29c6426942..8e5f6e168ca8f 100644
--- a/actionmailer/lib/action_mailer/railtie.rb
+++ b/actionmailer/lib/action_mailer/railtie.rb
@@ -71,6 +71,16 @@ class Railtie < Rails::Railtie # :nodoc:
     initializer "action_mailer.set_autoload_paths", before: :set_autoload_paths do |app|
       options = app.config.action_mailer
       app.config.paths["test/mailers/previews"].concat(options.preview_paths)
+
+      # Preview paths configuration needs a pass.
+      #
+      # config.paths is cached as soon as it is accessed. Therefore, mutating
+      # paths["test/mailers/previews"] does not guarantee config.autoload_paths
+      # is going to include them.
+      #
+      # If config.paths was accessed before, config.autoload_paths is going to
+      # have whatever paths["test/mailers/previews"] had when cached.
+      app.config.autoload_paths.concat(options.preview_paths)
     end
 
     initializer "action_mailer.compile_config_methods" do
diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index 719e5dbea5419..f02771b467ff8 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,3 +1,13 @@
+*   `config/application.rb` now includes
+
+    ```ruby
+    config.autoload_lib(ignore: %w(assets tasks))
+    ```
+
+    In practice, this means that new 7.1 applications autoload from `lib` out of the box.
+
+    *Xavier Noria*
+
 *   Add an option to start rails console in sandbox mode by default
 
     `sandbox_by_default` option is added to start rails console in sandbox
diff --git a/railties/lib/rails/engine/configuration.rb b/railties/lib/rails/engine/configuration.rb
index 51ffeea826acd..c3efc74e69256 100644
--- a/railties/lib/rails/engine/configuration.rb
+++ b/railties/lib/rails/engine/configuration.rb
@@ -50,6 +50,9 @@ def paths
           paths.add "app/mailers",         eager_load: true
           paths.add "app/views"
 
+          # If you add more lib subdirectories here that should not be managed
+          # by the main autoloader, please update the config.autoload_lib call
+          # in the template that generates config/application.rb accordingly.
           paths.add "lib",                 load_path: true
           paths.add "lib/assets",          glob: "*"
           paths.add "lib/tasks",           glob: "**/*.rake"
diff --git a/railties/lib/rails/generators/rails/app/templates/config/application.rb.tt b/railties/lib/rails/generators/rails/app/templates/config/application.rb.tt
index a03c289d4019d..ca466a5ecdb0a 100644
--- a/railties/lib/rails/generators/rails/app/templates/config/application.rb.tt
+++ b/railties/lib/rails/generators/rails/app/templates/config/application.rb.tt
@@ -15,6 +15,9 @@ module <%= app_const_base %>
     config.load_defaults Rails::VERSION::STRING.to_f
 <%- end -%>
 
+    # Please, see https://guides.rubyonrails.org/autoloading_and_reloading_constants.html#config-autoload-lib-ignore.
+    config.autoload_lib(ignore: %w(assets tasks))
+
     # Configuration for the application, engines, and railties goes here.
     #
     # These settings can be overridden in specific environments using the files
diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index f0a67dafcf757..526863279db20 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -2119,8 +2119,10 @@ def index
       end
     end
 
-    test "autoload paths will exclude the configured javascript_path" do
-      add_to_config "config.javascript_path = 'webpack'"
+    test "autoload paths do not include custom config.javascript_paths" do
+      # The config.javascript_path assignment has to be in place before
+      # config.paths is accessed, since their compilation uses the value.
+      add_to_top_of_config "config.javascript_path = 'webpack'"
       app_dir("app/webpack")
 
       app "development"
@@ -2148,10 +2150,10 @@ def index
       assert_empty Rails.configuration.paths.load_paths - $LOAD_PATH
     end
 
-    test "autoload paths are not added to $LOAD_PATH by default" do
+    test "autoload paths are not added to $LOAD_PATH by default, except for lib" do
       app "development"
 
-      assert_empty ActiveSupport::Dependencies.autoload_paths & $LOAD_PATH
+      assert_equal ["#{app_path}/lib"], ActiveSupport::Dependencies.autoload_paths & $LOAD_PATH
 
       # Precondition, ensure we are testing something next.
       assert_not_empty Rails.configuration.paths.load_paths
@@ -2170,6 +2172,23 @@ def index
       assert_includes $LOAD_PATH, lib
     end
 
+    test "config.autoload_lib(...) is generated by default" do
+      app_file "lib/x.rb", "X = true"
+      app_file "lib/m/x.rb", "M::X = true"
+      app_file "lib/assets/x.rb", "Assets::X = true"
+      app_file "lib/tasks/x.rb", "Tasks::X = true"
+
+      app "development"
+
+      assert_includes Rails.application.config.autoload_paths, "#{app_path}/lib"
+      assert_includes Rails.application.config.eager_load_paths, "#{app_path}/lib"
+
+      assert X
+      assert M::X
+      assert_raises(NameError) { Assets }
+      assert_raises(NameError) { Tasks }
+    end
+
     test "autoload paths can be set in the config file of the environment" do
       app_dir "custom_autoload_path"
       app_dir "custom_autoload_once_path"
@@ -2197,6 +2216,7 @@ def index
         app_file "lib/tasks/x.rb", "Tasks::X = true"
         app_file "lib/generators/x.rb", "Generators::X = true"
 
+        remove_from_config "config\\.#{method_name}.*"
         add_to_config "config.#{method_name}(ignore: %w(tasks generators))"
 
         app "development"
@@ -2215,6 +2235,7 @@ def index
         app_file "lib/x.rb", "X = true"
         app_file "lib/tasks/x.rb", "Tasks::X = true"
 
+        remove_from_config "config\\.#{method_name}.*"
         add_to_config "config.#{method_name}(ignore: [])"
 
         app "development"
@@ -2232,6 +2253,7 @@ def index
         app_file "lib/x.rb", "X = true"
         app_file "lib/tasks/x.rb", "Tasks::X = true"
 
+        remove_from_config "config\\.#{method_name}.*"
         add_to_config "config.#{method_name}(ignore: 'tasks')"
 
         app "development"
@@ -2249,6 +2271,7 @@ def index
         app_file "lib/x.rb", "X = true"
         app_file "lib/tasks/x.rb", "Tasks::X = true"
 
+        remove_from_config "config\\.#{method_name}.*"
         add_to_config "config.#{method_name}(ignore: nil)"
 
         app "development"
diff --git a/railties/test/application/zeitwerk_integration_test.rb b/railties/test/application/zeitwerk_integration_test.rb
index 37c1723dc2b34..63c45bc915c35 100644
--- a/railties/test/application/zeitwerk_integration_test.rb
+++ b/railties/test/application/zeitwerk_integration_test.rb
@@ -234,27 +234,17 @@ module ZeitwerkIntegrationTestExtras; end
     $zeitwerk_integration_test_user = false
     app_file "app/models/user.rb", "class User; end; $zeitwerk_integration_test_user = true"
 
-    $zeitwerk_integration_test_lib = false
-    app_dir "lib"
-    app_file "lib/webhook_hacks.rb", "WebhookHacks = 1; $zeitwerk_integration_test_lib = true"
-
     $zeitwerk_integration_test_extras = false
     app_dir "extras"
     app_file "extras/websocket_hacks.rb", "WebsocketHacks = 1; $zeitwerk_integration_test_extras = true"
-
-    add_to_config "config.autoload_paths      << '#{app_path}/lib'"
     add_to_config "config.autoload_once_paths << '#{app_path}/extras'"
 
     boot("production")
 
     assert $zeitwerk_integration_test_user
-    assert_not $zeitwerk_integration_test_lib
     assert_not $zeitwerk_integration_test_extras
 
-    assert WebhookHacks
     assert WebsocketHacks
-
-    assert $zeitwerk_integration_test_lib
     assert $zeitwerk_integration_test_extras
   end