core/modules/rest/rest.services.yml                |  4 +++
 .../EventSubscriber/ResourceResponseSubscriber.php |  5 +--
 .../src/EventSubscriber/RestRouteSubscriber.php    | 40 ++++++++++++++++++++++
 .../EntityResource/EntityResourceTestBase.php      | 25 ++++++++++++++
 4 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/core/modules/rest/rest.services.yml b/core/modules/rest/rest.services.yml
index 869eb19..ebed915 100644
--- a/core/modules/rest/rest.services.yml
+++ b/core/modules/rest/rest.services.yml
@@ -31,3 +31,7 @@ services:
     arguments: ['@router.builder']
     tags:
       - { name: event_subscriber }
+  rest.route_subscriber:
+    class: Drupal\rest\EventSubscriber\RestRouteSubscriber
+    tags:
+      - { name: event_subscriber }
diff --git a/core/modules/rest/src/EventSubscriber/ResourceResponseSubscriber.php b/core/modules/rest/src/EventSubscriber/ResourceResponseSubscriber.php
index 5cb887b..1223be0 100644
--- a/core/modules/rest/src/EventSubscriber/ResourceResponseSubscriber.php
+++ b/core/modules/rest/src/EventSubscriber/ResourceResponseSubscriber.php
@@ -196,8 +196,9 @@ protected function flattenResponse(ResourceResponseInterface $response) {
    * {@inheritdoc}
    */
   public static function getSubscribedEvents() {
-    // Run shortly before \Drupal\Core\EventSubscriber\FinishResponseSubscriber.
-    $events[KernelEvents::RESPONSE][] = ['onResponse', 5];
+    // Run before \Drupal\dynamic_page_cache\EventSubscriber\DynamicPageCacheSubscriber
+    // (priority 100), so that Dynamic Page Cache can cache flattened responses.
+    $events[KernelEvents::RESPONSE][] = ['onResponse', 128];
     return $events;
   }
 
diff --git a/core/modules/rest/src/EventSubscriber/RestRouteSubscriber.php b/core/modules/rest/src/EventSubscriber/RestRouteSubscriber.php
new file mode 100644
index 0000000..bd81370
--- /dev/null
+++ b/core/modules/rest/src/EventSubscriber/RestRouteSubscriber.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Drupal\rest\EventSubscriber;
+
+use Drupal\Core\Routing\RouteSubscriberBase;
+use Drupal\Core\Routing\RoutingEvents;
+use Symfony\Component\Routing\RouteCollection;
+
+/**
+ * Performs certain alterations to REST routes.
+ */
+class RestRouteSubscriber extends RouteSubscriberBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function alterRoutes(RouteCollection $collection) {
+    foreach ($collection->all() as $name => $route) {
+      // Removes the '_admin_route' route option from each REST route that had
+      // it added by \Drupal\system\EventSubscriber\AdminRouteSubscriber.
+      if (strpos($name, 'rest.') === 0 && $route->hasOption('_admin_route')) {
+        $route->setOption('_admin_route', FALSE);
+      }
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents() {
+    $events = parent::getSubscribedEvents();
+
+    // Use a very low priority to run as late as possible. Especially use a
+    // lower priority than \Drupal\system\EventSubscriber\AdminRouteSubscriber.
+    $events[RoutingEvents::ALTER] = ['onAlterRoutes', -1000];
+
+    return $events;
+  }
+
+}
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
index 53796c8..b01cd83 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/EntityResourceTestBase.php
@@ -4,11 +4,13 @@
 
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Cache\Cache;
+use Drupal\Core\Cache\CacheableResponseInterface;
 use Drupal\Core\Config\Entity\ConfigEntityInterface;
 use Drupal\Core\Entity\FieldableEntityInterface;
 use Drupal\Core\Url;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\rest\ResourceResponseInterface;
 use Drupal\Tests\rest\Functional\ResourceTestBase;
 use GuzzleHttp\RequestOptions;
 use Psr\Http\Message\ResponseInterface;
@@ -386,6 +388,8 @@ public function testGet() {
     // 200 for well-formed HEAD request.
     $response = $this->request('HEAD', $url, $request_options);
     $this->assertResourceResponse(200, '', $response);
+    $this->assertTrue($response->hasHeader('X-Drupal-Dynamic-Cache'));
+    $this->assertSame(['MISS'], $response->getHeader('X-Drupal-Dynamic-Cache'));
     if (!$this->account) {
       $this->assertSame(['MISS'], $response->getHeader('X-Drupal-Cache'));
     }
@@ -395,13 +399,34 @@ public function testGet() {
     $head_headers = $response->getHeaders();
 
     // 200 for well-formed GET request. Page Cache hit because of HEAD request.
+    // Same for Dynamic Page Cache hit.
     $response = $this->request('GET', $url, $request_options);
     $this->assertResourceResponse(200, FALSE, $response);
+    $this->assertTrue($response->hasHeader('X-Drupal-Dynamic-Cache'));
     if (!static::$auth) {
       $this->assertSame(['HIT'], $response->getHeader('X-Drupal-Cache'));
+      $this->assertSame(['MISS'], $response->getHeader('X-Drupal-Dynamic-Cache'));
     }
     else {
       $this->assertFalse($response->hasHeader('X-Drupal-Cache'));
+      $this->assertSame(['HIT'], $response->getHeader('X-Drupal-Dynamic-Cache'));
+      // Assert that Dynamic Page Cache did not store a ResourceResponse object,
+      // which needs serialization after every cache hit. Instead, it should
+      // contain a flattened response. Otherwise performance suffers.
+      // @see \Drupal\rest\EventSubscriber\ResourceResponseSubscriber::flattenResponse()
+      $cache_items = $this->container->get('database')
+        ->query("SELECT cid, data FROM {cache_dynamic_page_cache} WHERE cid LIKE :pattern", [
+          ':pattern' => '%[route]=rest.%',
+        ])
+        ->fetchAllAssoc('cid');
+      foreach ($cache_items as $cid => $cache_item) {
+        $cached_data = unserialize($cache_item->data);
+        if (!isset($cached_data['#cache_redirect'])) {
+          $cached_response = $cached_data['#response'];
+          $this->assertNotInstanceOf(ResourceResponseInterface::class, $cached_response);
+          $this->assertInstanceOf(CacheableResponseInterface::class, $cached_response);
+        }
+      }
     }
     $cache_tags_header_value = $response->getHeader('X-Drupal-Cache-Tags')[0];
     $this->assertEquals($this->getExpectedCacheTags(), empty($cache_tags_header_value) ? [] : explode(' ', $cache_tags_header_value));