diff --git a/core/includes/config.inc b/core/includes/config.inc
index 51476b7..771de70 100644
--- a/core/includes/config.inc
+++ b/core/includes/config.inc
@@ -65,7 +65,7 @@ function config_get_storage_names_with_prefix($prefix = '') {
  *   A configuration object.
  */
 function config($name) {
-  return drupal_container()->get('config.factory')->get($name)->load();
+  return drupal_container()->get('config.factory')->get($name);
 }
 
 /**
@@ -155,14 +155,9 @@ function config_import_invoke_owner(array $config_changes, StorageInterface $sou
       // handle the configuration change.
       $handled_by_module = FALSE;
       if (module_hook($module, 'config_import_' . $op)) {
-        $old_config = new Config($storage_dispatcher);
-        $old_config
-          ->setName($name)
-          ->load();
-
+        $old_config = new Config($name, $storage_dispatcher);
         $data = $source_storage->read($name);
-        $new_config = new Config($storage_dispatcher);
-        $new_config->setName($name);
+        $new_config = new Config($name, $storage_dispatcher);
         if ($data !== FALSE) {
           $new_config->setData($data);
         }
diff --git a/core/lib/Drupal/Core/Config/Config.php b/core/lib/Drupal/Core/Config/Config.php
index a749a4b..12e47f4 100644
--- a/core/lib/Drupal/Core/Config/Config.php
+++ b/core/lib/Drupal/Core/Config/Config.php
@@ -31,7 +31,17 @@ class Config {
    *
    * @var array
    */
-  protected $data = array();
+  protected $data;
+
+  /**
+   * The overridden data of the configuration object.
+   */
+  protected $override;
+
+  /**
+   * The current runtime data ($data + $override)
+   */
+  protected $current;
 
   /**
    * The injected storage dispatcher object.
@@ -43,11 +53,14 @@ class Config {
   /**
    * Constructs a configuration object.
    *
+   * @param $name
+   *   The name of this configuration object.
    * @param Drupal\Core\Config\StorageDispatcher $storageDispatcher
    *   A storage dispatcher object to use for reading and writing the
    *   configuration data.
    */
-  public function __construct(StorageDispatcher $storageDispatcher) {
+  public function __construct($name, StorageDispatcher $storageDispatcher) {
+    $this->name = $name;
     $this->storageDispatcher = $storageDispatcher;
   }
 
@@ -59,17 +72,10 @@ class Config {
   }
 
   /**
-   * Sets the name of this configuration object.
-   */
-  public function setName($name) {
-    $this->name = $name;
-    return $this;
-  }
-
-  /**
    * Returns whether this configuration object is new.
    */
   public function isNew() {
+    $this->build();
     return $this->isNew;
   }
 
@@ -101,27 +107,18 @@ class Config {
    *   The data that was requested.
    */
   public function get($key = '') {
-    global $conf;
-
-    $name = $this->getName();
-    if (isset($conf[$name])) {
-      $merged_data = drupal_array_merge_deep($this->data, $conf[$name]);
-    }
-    else {
-      $merged_data = $this->data;
-    }
-
+    $this->build();
     if (empty($key)) {
-      return $merged_data;
+      return $this->current;
     }
     else {
       $parts = explode('.', $key);
       if (count($parts) == 1) {
-        return isset($merged_data[$key]) ? $merged_data[$key] : NULL;
+        return isset($this->current[$key]) ? $this->current[$key] : NULL;
       }
       else {
         $key_exists = NULL;
-        $value = drupal_array_get_nested_value($merged_data, $parts, $key_exists);
+        $value = drupal_array_get_nested_value($this->current, $parts, $key_exists);
         return $key_exists ? $value : NULL;
       }
     }
@@ -135,7 +132,18 @@ class Config {
    */
   public function setData(array $data) {
     $this->data = $data;
-    return $this;
+    return $this->rebuild();
+  }
+
+  /**
+   * Sets some values for this configuration object only for this request.
+   *
+   * @param array $data
+   *   The overrideen values of the configuration data.
+   */
+  public function setOverride(array $data) {
+    $this->override = $data;
+    return $this->rebuild();
   }
 
   /**
@@ -159,7 +167,7 @@ class Config {
     else {
       drupal_array_set_nested_value($this->data, $parts, $value);
     }
-    return $this;
+    return $this->rebuild();
   }
 
   /**
@@ -208,6 +216,7 @@ class Config {
    *   Name of the key whose value should be unset.
    */
   public function clear($key) {
+    $this->build();
     $parts = explode('.', $key);
     if (count($parts) == 1) {
       unset($this->data[$key]);
@@ -215,7 +224,7 @@ class Config {
     else {
       drupal_array_unset_nested_value($this->data, $parts);
     }
-    return $this;
+    return $this->rebuild();
   }
 
   /**
@@ -238,10 +247,11 @@ class Config {
    * Saves the configuration object.
    */
   public function save() {
+    $this->build();
     $this->sortByKey($this->data);
     $this->storageDispatcher->selectStorage('write', $this->name)->write($this->name, $this->data);
     $this->isNew = FALSE;
-    return $this;
+    return $this->rebuild();
   }
 
   /**
@@ -271,6 +281,32 @@ class Config {
     $this->data = array();
     $this->storageDispatcher->selectStorage('write', $this->name)->delete($this->name);
     $this->isNew = TRUE;
+    return $this->rebuild();
+  }
+
+  /**
+   * Build the data for this configuration object.
+   *
+   * Loads the base data if not loaded, and builds the current runtime configuration
+   * computing the overridden values.
+   */
+  public function build() {
+    if (!isset($this->current)) {
+      if (!isset($this->data)) {
+        $this->load();
+      }
+      $this->current = $this->data;
+      if (!empty($this->override)) {
+        $this->current = drupal_array_merge_deep($this->current, $this->override);
+      }
+    }
+    return $this;
+  }
+  /**
+   * Mark the current data to be rebuilt.
+   */
+  public function rebuild() {
+    unset($this->current);
     return $this;
   }
 }
diff --git a/core/lib/Drupal/Core/Config/ConfigFactory.php b/core/lib/Drupal/Core/Config/ConfigFactory.php
index 1fbca62..d6b046c 100644
--- a/core/lib/Drupal/Core/Config/ConfigFactory.php
+++ b/core/lib/Drupal/Core/Config/ConfigFactory.php
@@ -50,6 +50,8 @@ class ConfigFactory {
    *   A configuration object with the given $name.
    */
   public function get($name) {
+    global $conf;
+
     // @todo Caching the instantiated objects per name might cut off a fair
     //   amount of CPU time and memory. Only the data within the configuration
     //   object changes, so the additional cost of instantiating duplicate
@@ -68,7 +70,11 @@ class ConfigFactory {
     // @todo The decrease of CPU time is interesting, since that means that
     //   ContainerBuilder involves plenty of function calls (which are known to
     //   be slow in PHP).
-    $config = new Config($this->storageDispatcher);
-    return $config->setName($name);
+    $config = new Config($name, $this->storageDispatcher);
+    // Add any overridden values in global $conf
+    if (isset($conf[$name])) {
+      $config->setOverride($conf[$name]);
+    }
+    return $config;
   }
 }