diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampAgoFormatter.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampAgoFormatter.php
new file mode 100644
index 0000000..571d616
--- /dev/null
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/TimestampAgoFormatter.php
@@ -0,0 +1,95 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\Field\Plugin\Field\FieldFormatter\TimestampAgoFormatter.
+ */
+
+namespace Drupal\Core\Field\Plugin\Field\FieldFormatter;
+
+use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\Field\FieldDefinitionInterface;
+use Drupal\Core\Field\FieldItemListInterface;
+use Drupal\Core\Field\FormatterBase;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Plugin implementation of the 'timestamp' formatter as time ago.
+ *
+ * @FieldFormatter(
+ *   id = "timestamp_ago",
+ *   label = @Translation("Time ago"),
+ *   field_types = {
+ *     "timestamp",
+ *     "created",
+ *     "updated",
+ *   }
+ * )
+ */
+class TimestampAgoFormatter extends FormatterBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * Constructs a TimestampAgoFormatter object.
+   *
+   * @param string $plugin_id
+   *   The plugin_id for the formatter.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
+   *   The definition of the field to which the formatter is associated.
+   * @param array $settings
+   *   The formatter settings.
+   * @param string $label
+   *   The formatter label display setting.
+   * @param string $view_mode
+   *   The view mode.
+   * @param array $third_party_settings
+   *   Any third party settings settings.
+   * @param \Drupal\Core\Datetime\DateFormatter $date_formatter
+   *    The date formatter service.
+   */
+  public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, DateFormatter $date_formatter) {
+    parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings);
+
+    $this->dateFormatter = $date_formatter;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    // @see \Drupal\Core\Field\FormatterPluginManager::createInstance().
+    return new static(
+      $plugin_id,
+      $plugin_definition,
+      $configuration['field_definition'],
+      $configuration['settings'],
+      $configuration['label'],
+      $configuration['view_mode'],
+      $configuration['third_party_settings'],
+      $container->get('date.formatter')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function viewElements(FieldItemListInterface $items) {
+    $elements = array();
+
+    foreach ($items as $delta => $item) {
+      if ($item->value) {
+        $updated = $this->t('@time ago', array('@time' => $this->dateFormatter->formatInterval(REQUEST_TIME - $item->value)));
+      }
+      else {
+        $updated = t('never');
+      }
+
+      $elements[$delta] = array('#markup' => $updated);
+    }
+
+    return $elements;
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/UriLinkFormatter.php b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/UriLinkFormatter.php
index a6522e9..df12a53 100644
--- a/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/UriLinkFormatter.php
+++ b/core/lib/Drupal/Core/Field/Plugin/Field/FieldFormatter/UriLinkFormatter.php
@@ -35,8 +35,6 @@ public function viewElements(FieldItemListInterface $items) {
         '#type' => 'link',
         '#href' => $item->value,
         '#title' => $item->value,
-        // @todo Make this configurable?
-        '#options' => array('absolute' => TRUE),
       );
     }
 
diff --git a/core/modules/aggregator/aggregator.module b/core/modules/aggregator/aggregator.module
index 024a36b..7cf2e73 100644
--- a/core/modules/aggregator/aggregator.module
+++ b/core/modules/aggregator/aggregator.module
@@ -105,13 +105,6 @@ function aggregator_entity_extra_field_info() {
         'description' => t('Items associated with this feed'),
         'weight' => 0,
       ),
-      // @todo Move to a formatter after https://drupal.org/node/2226493 which
-      //   provides the TimestampFormatter is in.
-      'checked' => array(
-        'label' => t('Last checked'),
-        'description' => t('When this feed was last checked'),
-        'weight' => 1,
-      ),
       'image' => array(
         'label' => t('Image'),
         'description' => t('The feed image'),
@@ -133,13 +126,6 @@ function aggregator_entity_extra_field_info() {
         'description' => t('The aggregator feed entity associated with this item'),
         'weight' => 0,
       ),
-      // @todo Move to a formatter after https://drupal.org/node/2226493 which
-      //   provides the TimestampFormatter is in.
-      'timestamp' => array(
-        'label' => t('Date'),
-        'description' => t('Posted date of the feed as time ago'),
-        'weight' => 1,
-      ),
       // @todo Move to a formatter at https://drupal.org/node/2149845.
       'description' => array(
         'label' => t('Description'),
diff --git a/core/modules/aggregator/aggregator.theme.inc b/core/modules/aggregator/aggregator.theme.inc
index 53ab9fd..f20dbf5 100644
--- a/core/modules/aggregator/aggregator.theme.inc
+++ b/core/modules/aggregator/aggregator.theme.inc
@@ -27,7 +27,6 @@ function template_preprocess_aggregator_item(&$variables) {
 
   $variables['url'] = check_url($item->getLink());
   $variables['title'] = String::checkPlain($item->label());
-  $variables['attributes']['class'][] = 'feed-item';
 }
 
 /**
@@ -102,8 +101,6 @@ function template_preprocess_aggregator_feed(&$variables) {
       ),
     );
   }
-
-  $variables['attributes']['class'][] = 'feed-source';
 }
 
 /**
diff --git a/core/modules/aggregator/config/install/entity.view_display.aggregator_feed.aggregator_feed.summary.yml b/core/modules/aggregator/config/install/core.entity_view_display..aggregator_feed.aggregator_feed.summary.yml
similarity index 84%
rename from core/modules/aggregator/config/install/entity.view_display.aggregator_feed.aggregator_feed.summary.yml
rename to core/modules/aggregator/config/install/core.entity_view_display..aggregator_feed.aggregator_feed.summary.yml
index 3097653..f9f14b8 100644
--- a/core/modules/aggregator/config/install/entity.view_display.aggregator_feed.aggregator_feed.summary.yml
+++ b/core/modules/aggregator/config/install/core.entity_view_display..aggregator_feed.aggregator_feed.summary.yml
@@ -13,6 +13,6 @@ hidden:
 status: true
 dependencies:
   entity:
-    - entity.view_mode.aggregator_feed.summary
+    - core.entity_view_mode.aggregator_feed.summary
   module:
     - aggregator
diff --git a/core/modules/aggregator/config/install/entity.view_display.aggregator_item.aggregator_item.summary.yml b/core/modules/aggregator/config/install/core.entity_view_display..aggregator_item.aggregator_item.summary.yml
similarity index 84%
rename from core/modules/aggregator/config/install/entity.view_display.aggregator_item.aggregator_item.summary.yml
rename to core/modules/aggregator/config/install/core.entity_view_display..aggregator_item.aggregator_item.summary.yml
index dcbd77c..c29ffeb 100644
--- a/core/modules/aggregator/config/install/entity.view_display.aggregator_item.aggregator_item.summary.yml
+++ b/core/modules/aggregator/config/install/core.entity_view_display..aggregator_item.aggregator_item.summary.yml
@@ -13,6 +13,6 @@ hidden:
 status: true
 dependencies:
   entity:
-    - entity.view_mode.aggregator_item.summary
+    - core.entity_view_mode.aggregator_item.summary
   module:
     - aggregator
diff --git a/core/modules/aggregator/config/install/entity.view_mode.aggregator_feed.summary.yml b/core/modules/aggregator/config/install/core.entity_view_mode.aggregator_feed.summary.yml
similarity index 100%
rename from core/modules/aggregator/config/install/entity.view_mode.aggregator_feed.summary.yml
rename to core/modules/aggregator/config/install/core.entity_view_mode.aggregator_feed.summary.yml
diff --git a/core/modules/aggregator/src/Entity/Feed.php b/core/modules/aggregator/src/Entity/Feed.php
index 6fe48e3..5a33b71 100644
--- a/core/modules/aggregator/src/Entity/Feed.php
+++ b/core/modules/aggregator/src/Entity/Feed.php
@@ -36,8 +36,8 @@
  *     "canonical" = "entity.aggregator_feed.canonical",
  *     "edit-form" = "entity.aggregator_feed.edit_form",
  *     "delete-form" = "entity.aggregator_feed.delete_form",
- *     "admin-form" = "aggregator.admin_overview",
  *   },
+ *   field_ui_base_route = "aggregator.admin_overview",
  *   base_table = "aggregator_feed",
  *   fieldable = TRUE,
  *   render_cache = FALSE,
@@ -185,7 +185,13 @@ public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
     $fields['checked'] = BaseFieldDefinition::create('timestamp')
       ->setLabel(t('Checked'))
       ->setDescription(t('Last time feed was checked for new items, as Unix timestamp.'))
-      ->setDefaultValue(0);
+      ->setDefaultValue(0)
+      ->setDisplayOptions('view', array(
+        'label' => 'inline',
+        'type' => 'timestamp_ago',
+        'weight' => 1,
+      ))
+      ->setDisplayConfigurable('view', TRUE);
 
     $fields['queued'] = BaseFieldDefinition::create('timestamp')
       ->setLabel(t('Queued'))
diff --git a/core/modules/aggregator/src/Entity/Item.php b/core/modules/aggregator/src/Entity/Item.php
index 43f6de4..1d7fc5c 100644
--- a/core/modules/aggregator/src/Entity/Item.php
+++ b/core/modules/aggregator/src/Entity/Item.php
@@ -92,8 +92,14 @@ public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
       ->setDescription(t('The body of the feed item.'));
 
     $fields['timestamp'] = BaseFieldDefinition::create('created')
-      ->setLabel(t('Posted timestamp'))
-      ->setDescription(t('Posted date of the feed item, as a Unix timestamp.'));
+      ->setLabel(t('Posted on'))
+      ->setDescription(t('Posted date of the feed item, as a Unix timestamp.'))
+      ->setDisplayOptions('view', array(
+        'label' => 'hidden',
+        'type' => 'timestamp_ago',
+        'weight' => 1,
+      ))
+      ->setDisplayConfigurable('view', TRUE);
 
     // @todo Convert to a real UUID field in https://drupal.org/node/2149851.
     $fields['guid'] = BaseFieldDefinition::create('string_long')
diff --git a/core/modules/aggregator/src/FeedViewBuilder.php b/core/modules/aggregator/src/FeedViewBuilder.php
index 73e6a96..84fa2ad 100644
--- a/core/modules/aggregator/src/FeedViewBuilder.php
+++ b/core/modules/aggregator/src/FeedViewBuilder.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\aggregator;
 
-use Drupal\Core\Datetime\DateFormatter;
 use Drupal\Core\Entity\EntityInterface;
 use Drupal\Core\Entity\EntityManagerInterface;
 use Drupal\Core\Entity\EntityTypeInterface;
@@ -30,13 +29,12 @@ class FeedViewBuilder extends EntityViewBuilder {
    *   The entity manager service.
    * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
    *   The language manager.
-   * @param \Drupal\Core\Datetime\Date $date_formatter
-   *    The date formatter service.
+   * @param \Drupal\Core\Config\Config $config
+   *    The 'aggregator.settings' config.
    */
-  public function __construct(EntityTypeInterface $entity_type, EntityManagerInterface $entity_manager, LanguageManagerInterface $language_manager, Config $config, DateFormatter $date_formatter) {
+  public function __construct(EntityTypeInterface $entity_type, EntityManagerInterface $entity_manager, LanguageManagerInterface $language_manager, Config $config) {
     parent::__construct($entity_type, $entity_manager, $language_manager);
     $this->config = $config;
-    $this->dateFormatter = $date_formatter;
   }
 
   /**
@@ -47,8 +45,7 @@ public static function createInstance(ContainerInterface $container, EntityTypeI
       $entity_type,
       $container->get('entity.manager'),
       $container->get('language_manager'),
-      $container->get('config.factory')->get('aggregator.settings'),
-      $container->get('date.formatter')
+      $container->get('config.factory')->get('aggregator.settings')
     );
   }
 
@@ -80,22 +77,6 @@ public function buildComponents(array &$build, array $entities, array $displays,
         }
       }
 
-      if ($display->getComponent('checked')) {
-        // Render the checked timestamp as time ago.
-        $last_checked = $entity->getLastCheckedTime();
-        if ($last_checked) {
-          $updated = t('@time ago', array('@time' => $this->dateFormatter->formatInterval(REQUEST_TIME - $last_checked)));
-        }
-        else {
-          $updated = t('never');
-        }
-        $build[$id]['checked'] = array(
-          '#markup' => t('<em>Updated:</em> @updated', array('@updated' => $updated)),
-          '#prefix' => '<div class="feed-updated">',
-          '#suffix' => '</div>',
-        );
-      }
-
       if ($display->getComponent('description')) {
         $build[$id]['description'] = array(
           '#markup' => aggregator_filter_xss($entity->getDescription()),
diff --git a/core/modules/aggregator/src/ItemViewBuilder.php b/core/modules/aggregator/src/ItemViewBuilder.php
index 565e52d..0a0b5ce 100644
--- a/core/modules/aggregator/src/ItemViewBuilder.php
+++ b/core/modules/aggregator/src/ItemViewBuilder.php
@@ -8,13 +8,7 @@
 namespace Drupal\aggregator;
 
 use Drupal\Component\Utility\String;
-use Drupal\Core\Datetime\DateFormatter;
-use Drupal\Core\Entity\EntityInterface;
-use Drupal\Core\Entity\EntityManagerInterface;
-use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Entity\EntityViewBuilder;
-use Drupal\Core\Language\LanguageManagerInterface;
-use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
  * Render controller for aggregator feed items.
@@ -22,35 +16,6 @@
 class ItemViewBuilder extends EntityViewBuilder {
 
   /**
-   * Constructs a new ItemViewBuilder.
-   *
-   * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
-   *   The entity type definition.
-   * @param \Drupal\Core\Entity\EntityManagerInterface $entity_manager
-   *   The entity manager service.
-   * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
-   *   The language manager.
-   * @param \Drupal\Core\Datetime\Date $date_formatter
-   *    The date formatter service.
-   */
-  public function __construct(EntityTypeInterface $entity_type, EntityManagerInterface $entity_manager, LanguageManagerInterface $language_manager, DateFormatter $date_formatter) {
-    parent::__construct($entity_type, $entity_manager, $language_manager);
-    $this->dateFormatter = $date_formatter;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public static function createInstance(ContainerInterface $container, EntityTypeInterface $entity_type) {
-    return new static(
-      $entity_type,
-      $container->get('entity.manager'),
-      $container->get('language_manager'),
-      $container->get('date.formatter')
-    );
-  }
-
-  /**
    * {@inheritdoc}
    */
   public function buildComponents(array &$build, array $entities, array $displays, $view_mode, $langcode = NULL) {
@@ -79,37 +44,6 @@ public function buildComponents(array &$build, array $entities, array $displays,
         );
       }
 
-      if ($display->getComponent('timestamp')) {
-        if ($view_mode == 'summary') {
-          // Always render the timestamp as time ago on summary.
-          $build[$id]['timestamp'] = array(
-            '#theme' => 'time',
-            '#attributes' => array(
-              'datetime' => $this->dateFormatter->format($entity->getPostedTime(), 'html_datetime', '', 'UTC'),
-              'class' => array('feed-item-age'),
-            ),
-            '#text' => t('%age old', array('%age' => $this->dateFormatter->formatInterval(REQUEST_TIME - $entity->getPostedTime()))),
-            '#html' => TRUE,
-          );
-        }
-        else {
-          // On full mode only display as time ago only if the post is in the
-          // same month.
-          $posted_time = $entity->getPostedTime();
-          if (date('Ymd', $posted_time) == date('Ymd')) {
-            $date = t('%ago ago', array('%ago' => $this->dateFormatter->formatInterval(REQUEST_TIME - $posted_time)));
-          }
-          else {
-            $date = $this->dateFormatter->format($posted_time, 'medium');
-          }
-          $build[$id]['timestamp'] = array(
-            '#markup' => $date,
-            '#prefix' => '<span class="feed-item-date">',
-            '#suffix' => '</span>',
-          );
-        }
-      }
-
       if ($display->getComponent('description')) {
         $build[$id]['description'] = array(
           '#markup' => aggregator_filter_xss($entity->getDescription()),
diff --git a/core/modules/aggregator/templates/aggregator-feed.html.twig b/core/modules/aggregator/templates/aggregator-feed.html.twig
index 4f8d400..8cd7c11 100644
--- a/core/modules/aggregator/templates/aggregator-feed.html.twig
+++ b/core/modules/aggregator/templates/aggregator-feed.html.twig
@@ -19,7 +19,7 @@
  * @ingroup themeable
  */
 #}
-<div{{ attributes }}>
+<div{{ attributes.addClass('aggregator-feed') }}>
 
   {{ title_prefix }}
   {% if not full %}
diff --git a/core/modules/aggregator/templates/aggregator-item.html.twig b/core/modules/aggregator/templates/aggregator-item.html.twig
index 5ad6b4d..8f31937 100644
--- a/core/modules/aggregator/templates/aggregator-item.html.twig
+++ b/core/modules/aggregator/templates/aggregator-item.html.twig
@@ -16,7 +16,7 @@
  * @ingroup themeable
  */
 #}
-<div{{ attributes }}>
+<div{{ attributes.addClass('aggregator-item') }}>
   {{ title_prefix }}
   <h3 class="feed-item-title">
     <a href="{{ url }}">{{ title }}</a>