core/modules/comment/src/Tests/CommentTranslationUITest.php   |  1 +
 .../src/Tests/ContentTranslationUITestBase.php                |  2 +-
 .../src/Tests/MenuLinkContentTranslationUITest.php            |  2 +-
 core/modules/node/src/Tests/NodeBlockFunctionalTest.php       | 11 ++++++-----
 core/modules/node/src/Tests/NodeTranslationUITest.php         |  1 +
 .../smart_cache/src/EventSubscriber/SmartCacheSubscriber.php  | 11 +++++++++--
 .../tests/smart_cache_test/src/SmartCacheTestController.php   |  2 +-
 core/modules/system/src/Tests/Routing/RouterTest.php          |  4 +++-
 core/modules/system/src/Tests/System/TokenReplaceWebTest.php  |  5 +++--
 core/modules/toolbar/src/Tests/ToolbarCacheContextsTest.php   |  2 ++
 core/modules/tracker/src/Tests/TrackerTest.php                |  7 ++++---
 11 files changed, 32 insertions(+), 16 deletions(-)

diff --git a/core/modules/comment/src/Tests/CommentTranslationUITest.php b/core/modules/comment/src/Tests/CommentTranslationUITest.php
index dc1bf9e..c18c550 100644
--- a/core/modules/comment/src/Tests/CommentTranslationUITest.php
+++ b/core/modules/comment/src/Tests/CommentTranslationUITest.php
@@ -40,6 +40,7 @@ class CommentTranslationUITest extends ContentTranslationUITestBase {
     'theme',
     'user.permissions',
     'timezone',
+    'url.query_args:_wrapper_format',
     'url.query_args.pagers:0',
     'user.roles'
   ];
diff --git a/core/modules/content_translation/src/Tests/ContentTranslationUITestBase.php b/core/modules/content_translation/src/Tests/ContentTranslationUITestBase.php
index 5faa85c..02cc0d3 100644
--- a/core/modules/content_translation/src/Tests/ContentTranslationUITestBase.php
+++ b/core/modules/content_translation/src/Tests/ContentTranslationUITestBase.php
@@ -44,7 +44,7 @@
    *
    * @var string[]
    */
-  protected $defaultCacheContexts = ['languages:language_interface', 'theme', 'user.permissions'];
+  protected $defaultCacheContexts = ['languages:language_interface', 'theme', 'url.query_args:_wrapper_format', 'user.permissions'];
 
   /**
    * Tests the basic translation UI.
diff --git a/core/modules/menu_link_content/src/Tests/MenuLinkContentTranslationUITest.php b/core/modules/menu_link_content/src/Tests/MenuLinkContentTranslationUITest.php
index 615da6b..f72cb29 100644
--- a/core/modules/menu_link_content/src/Tests/MenuLinkContentTranslationUITest.php
+++ b/core/modules/menu_link_content/src/Tests/MenuLinkContentTranslationUITest.php
@@ -20,7 +20,7 @@ class MenuLinkContentTranslationUITest extends ContentTranslationUITestBase {
   /**
    * {inheritdoc}
    */
-  protected $defaultCacheContexts = ['languages:language_interface', 'theme', 'user.permissions', 'user.roles:authenticated'];
+  protected $defaultCacheContexts = ['languages:language_interface', 'theme', 'url.query_args:_wrapper_format', 'user.permissions', 'user.roles:authenticated'];
 
   /**
    * Modules to enable.
diff --git a/core/modules/node/src/Tests/NodeBlockFunctionalTest.php b/core/modules/node/src/Tests/NodeBlockFunctionalTest.php
index 13a835a..1cdb986 100644
--- a/core/modules/node/src/Tests/NodeBlockFunctionalTest.php
+++ b/core/modules/node/src/Tests/NodeBlockFunctionalTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\node\Tests;
 
 use Drupal\block\Entity\Block;
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\system\Tests\Cache\AssertPageCacheContextsAndTagsTrait;
 use Drupal\user\RoleInterface;
 
@@ -125,7 +126,7 @@ public function testRecentNodeBlock() {
     $this->assertText($node3->label(), 'Node found in block.');
     $this->assertText($node4->label(), 'Node found in block.');
 
-    $this->assertCacheContexts(['languages:language_content', 'languages:language_interface', 'theme', 'user']);
+    $this->assertCacheContexts(['languages:language_content', 'languages:language_interface', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'user']);
 
     // Enable the "Powered by Drupal" block only on article nodes.
     $edit = [
@@ -150,16 +151,16 @@ public function testRecentNodeBlock() {
     $this->drupalGet('');
     $label = $block->label();
     $this->assertNoText($label, 'Block was not displayed on the front page.');
-    $this->assertCacheContexts(['languages:language_content', 'languages:language_interface', 'theme', 'user', 'route']);
+    $this->assertCacheContexts(['languages:language_content', 'languages:language_interface', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'user', 'route']);
     $this->drupalGet('node/add/article');
     $this->assertText($label, 'Block was displayed on the node/add/article page.');
-    $this->assertCacheContexts(['languages:language_content', 'languages:language_interface', 'theme', 'user', 'route']);
+    $this->assertCacheContexts(['languages:language_content', 'languages:language_interface', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'user', 'route']);
     $this->drupalGet('node/' . $node1->id());
     $this->assertText($label, 'Block was displayed on the node/N when node is of type article.');
-    $this->assertCacheContexts(['languages:language_content', 'languages:language_interface', 'theme', 'user', 'route', 'timezone']);
+    $this->assertCacheContexts(['languages:language_content', 'languages:language_interface', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'user', 'route', 'timezone']);
     $this->drupalGet('node/' . $node5->id());
     $this->assertNoText($label, 'Block was not displayed on nodes of type page.');
-    $this->assertCacheContexts(['languages:language_content', 'languages:language_interface', 'theme', 'user', 'route', 'timezone']);
+    $this->assertCacheContexts(['languages:language_content', 'languages:language_interface', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'user', 'route', 'timezone']);
 
     $this->drupalLogin($this->adminUser);
     $this->drupalGet('admin/structure/block');
diff --git a/core/modules/node/src/Tests/NodeTranslationUITest.php b/core/modules/node/src/Tests/NodeTranslationUITest.php
index c392750..e909618 100644
--- a/core/modules/node/src/Tests/NodeTranslationUITest.php
+++ b/core/modules/node/src/Tests/NodeTranslationUITest.php
@@ -27,6 +27,7 @@ class NodeTranslationUITest extends ContentTranslationUITestBase {
   protected $defaultCacheContexts = [
     'languages:language_interface',
     'theme',
+    'url.query_args:_wrapper_format',
     'user.permissions',
     'route.menu_active_trails:account',
     'route.menu_active_trails:footer',
diff --git a/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php b/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php
index cc39e90..4edc76f 100644
--- a/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php
+++ b/core/modules/smart_cache/src/EventSubscriber/SmartCacheSubscriber.php
@@ -78,6 +78,13 @@ class SmartCacheSubscriber implements EventSubscriberInterface {
       'keys' => ['response'],
       'contexts' => [
         'route',
+        // Some routes' controllers rely on the request format (they don't have
+        // a separate route for each request format). Additionally, a controller
+        // may be returning a domain object that a KernelEvents::VIEW subscriber
+        // must turn into an actual response, but perhaps a format is being
+        // requested that the subscriber does not support.
+        // @see \Drupal\Core\EventSubscriber\AcceptNegotiation406::onViewDetect406()
+        'request_format',
       ],
       'bin' => 'smart_cache',
     ],
@@ -176,8 +183,8 @@ public function onResponse(FilterResponseEvent $event) {
       return;
     }
 
-    // Embed the response object in a render array so that SmartCache is able to
-    // cache it, handling cache redirection for us.
+    // Embed the response object in a render array so that RenderCache is able
+    // to cache it, handling cache redirection for us.
     $response_as_render_array = $this->responseToRenderArray($response);
     $this->renderCache->set($response_as_render_array, $this->smartCacheRedirectRenderArray);
 
diff --git a/core/modules/smart_cache/tests/smart_cache_test/src/SmartCacheTestController.php b/core/modules/smart_cache/tests/smart_cache_test/src/SmartCacheTestController.php
index 9bca72d..61cc45b 100644
--- a/core/modules/smart_cache/tests/smart_cache_test/src/SmartCacheTestController.php
+++ b/core/modules/smart_cache/tests/smart_cache_test/src/SmartCacheTestController.php
@@ -28,7 +28,7 @@ public function response() {
   }
 
   /**
-   * A route returning a Response object.
+   * A route returning a CacheableResponse object.
    *
    * @return \Drupal\Core\Cache\CacheableResponseInterface
    *   A CacheableResponseInterface object.
diff --git a/core/modules/system/src/Tests/Routing/RouterTest.php b/core/modules/system/src/Tests/Routing/RouterTest.php
index 207049f..86d823e 100644
--- a/core/modules/system/src/Tests/Routing/RouterTest.php
+++ b/core/modules/system/src/Tests/Routing/RouterTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\system\Tests\Routing;
 
 use Drupal\Core\Cache\Cache;
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\simpletest\WebTestBase;
 use Symfony\Component\HttpFoundation\Request;
@@ -32,6 +33,7 @@ class RouterTest extends WebTestBase {
    */
   public function testFinishResponseSubscriber() {
     $renderer_required_cache_contexts = ['languages:' . LanguageInterface::TYPE_INTERFACE, 'theme', 'user.permissions'];
+    $expected_cache_contexts = Cache::mergeContexts($renderer_required_cache_contexts, ['url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT]);
 
     // Confirm that the router can get to a controller.
     $this->drupalGet('router_test/test1');
@@ -47,7 +49,7 @@ public function testFinishResponseSubscriber() {
     $this->assertRaw('test2', 'The correct string was returned because the route was successful.');
     // Check expected headers from FinishResponseSubscriber.
     $headers = $this->drupalGetHeaders();
-    $this->assertEqual($headers['x-drupal-cache-contexts'], implode(' ', $renderer_required_cache_contexts));
+    $this->assertEqual($headers['x-drupal-cache-contexts'], implode(' ', $expected_cache_contexts));
     $this->assertEqual($headers['x-drupal-cache-tags'], 'config:user.role.anonymous rendered');
     // Confirm that the page wrapping is being added, so we're not getting a
     // raw body returned.
diff --git a/core/modules/system/src/Tests/System/TokenReplaceWebTest.php b/core/modules/system/src/Tests/System/TokenReplaceWebTest.php
index 7e9d60f..ba94e51 100644
--- a/core/modules/system/src/Tests/System/TokenReplaceWebTest.php
+++ b/core/modules/system/src/Tests/System/TokenReplaceWebTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\system\Tests\System;
 
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\simpletest\WebTestBase;
 use Drupal\system\Tests\Cache\AssertPageCacheContextsAndTagsTrait;
 
@@ -35,12 +36,12 @@ public function testTokens() {
     $this->drupalGet('token-test/' . $node->id());
     $this->assertText("Tokens: {$node->id()} {$account->id()}");
     $this->assertCacheTags(['node:1', 'rendered', 'user:2']);
-    $this->assertCacheContexts(['languages:language_interface', 'theme', 'user']);
+    $this->assertCacheContexts(['languages:language_interface', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'user']);
 
     $this->drupalGet('token-test-without-bubleable-metadata/' . $node->id());
     $this->assertText("Tokens: {$node->id()} {$account->id()}");
     $this->assertCacheTags(['node:1', 'rendered', 'user:2']);
-    $this->assertCacheContexts(['languages:language_interface', 'theme', 'user']);
+    $this->assertCacheContexts(['languages:language_interface', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'user']);
   }
 
 }
diff --git a/core/modules/toolbar/src/Tests/ToolbarCacheContextsTest.php b/core/modules/toolbar/src/Tests/ToolbarCacheContextsTest.php
index 277d312..759f646 100644
--- a/core/modules/toolbar/src/Tests/ToolbarCacheContextsTest.php
+++ b/core/modules/toolbar/src/Tests/ToolbarCacheContextsTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\toolbar\Tests;
 
 use Drupal\Core\Cache\Cache;
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\simpletest\WebTestBase;
 use Drupal\system\Tests\Cache\AssertPageCacheContextsAndTagsTrait;
 
@@ -109,6 +110,7 @@ protected function assertToolbarCacheContexts(array $cache_contexts, $message =
     $default_cache_contexts = [
       'languages:language_interface',
       'theme',
+      'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT,
     ];
     $cache_contexts = Cache::mergeContexts($default_cache_contexts, $cache_contexts);
 
diff --git a/core/modules/tracker/src/Tests/TrackerTest.php b/core/modules/tracker/src/Tests/TrackerTest.php
index aaf7bad..7742cfe 100644
--- a/core/modules/tracker/src/Tests/TrackerTest.php
+++ b/core/modules/tracker/src/Tests/TrackerTest.php
@@ -10,6 +10,7 @@
 use Drupal\comment\CommentInterface;
 use Drupal\comment\Tests\CommentTestTrait;
 use Drupal\Core\Cache\Cache;
+use Drupal\Core\EventSubscriber\MainContentViewSubscriber;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\field\Entity\FieldStorageConfig;
 use Drupal\node\Entity\Node;
@@ -83,7 +84,7 @@ function testTrackerAll() {
     $this->assertLink(t('My recent content'), 0, 'User tab shows up on the global tracker page.');
 
     // Assert cache contexts, specifically the pager and node access contexts.
-    $this->assertCacheContexts(['languages:language_interface', 'theme', 'url.query_args.pagers:0', 'user.node_grants:view', 'user.permissions', 'user.roles:authenticated']);
+    $this->assertCacheContexts(['languages:language_interface', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'url.query_args.pagers:0', 'user.node_grants:view', 'user.permissions', 'user.roles:authenticated']);
     // Assert cache tags for the visible node, node lists and comment lists.
     $expected_tags = Cache::mergeTags($published->getCacheTags(), $published->getOwner()->getCacheTags());
     $expected_tags = Cache::mergeTags($expected_tags, ['node_list', 'comment_list', 'rendered']);
@@ -149,7 +150,7 @@ function testTrackerUser() {
     $this->assertText($other_published_my_comment->label(), "Nodes that the user has commented on appear in the user's tracker listing.");
 
     // Assert cache contexts.
-    $this->assertCacheContexts(['languages:language_interface', 'theme', 'url.query_args.pagers:0', 'user', 'user.node_grants:view']);
+    $this->assertCacheContexts(['languages:language_interface', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'url.query_args.pagers:0', 'user', 'user.node_grants:view']);
     // Assert cache tags for the visible nodes (including owners) and node list
     // cache tag.
     $expected_tags = Cache::mergeTags($my_published->getCacheTags(), $my_published->getOwner()->getCacheTags());
@@ -158,7 +159,7 @@ function testTrackerUser() {
     $expected_tags = Cache::mergeTags($expected_tags, ['node_list', 'comment_list', 'rendered']);
 
     $this->assertCacheTags($expected_tags);
-    $this->assertCacheContexts(['languages:language_interface', 'theme', 'url.query_args.pagers:0', 'user', 'user.node_grants:view']);
+    $this->assertCacheContexts(['languages:language_interface', 'theme', 'url.query_args:' . MainContentViewSubscriber::WRAPPER_FORMAT, 'url.query_args.pagers:0', 'user', 'user.node_grants:view']);
 
     $this->assertLink($my_published->label());
     $this->assertNoLink($unpublished->label());