diff --git a/core/core.libraries.yml b/core/core.libraries.yml
index c8f432987b4a2c9ba0a54d653a0521fe13f1da52..48f2abced3d7e95b63d7c61202eae8c463540bbb 100644
--- a/core/core.libraries.yml
+++ b/core/core.libraries.yml
@@ -69,7 +69,7 @@ ckeditor5.editorDecoupled:
     - core/ckeditor5
     - core/ckeditor5.htmlSupport
 
-ckeditor5.internal:
+ckeditor5.essentials:
   remote: https://github.com/ckeditor/ckeditor5
   version: "35.1.0"
   license:
diff --git a/core/modules/ckeditor5/ckeditor5.ckeditor5.yml b/core/modules/ckeditor5/ckeditor5.ckeditor5.yml
index afcdbd7a7ded4b7fb08c01fd5a31d44c340450da..62ef19493dbabc25ac18e19ba6942e39543d48d5 100644
--- a/core/modules/ckeditor5/ckeditor5.ckeditor5.yml
+++ b/core/modules/ckeditor5/ckeditor5.ckeditor5.yml
@@ -9,8 +9,8 @@ ckeditor5_essentials:
       - essentials.Essentials
   drupal:
     label: Essentials
-    library: ckeditor5/drupal.ckeditor5.internal
-    admin_library: ckeditor5/admin.internal
+    library: ckeditor5/internal.drupal.ckeditor5.htmlEngine
+    admin_library: ckeditor5/internal.admin.essentials
     toolbar_items:
       undo:
         label: Undo
@@ -25,8 +25,8 @@ ckeditor5_paragraph:
     plugins: [paragraph.Paragraph]
   drupal:
     label: Paragraph
-    library: core/ckeditor5.internal
-    admin_library: ckeditor5/admin.internal
+    library: core/ckeditor5.essentials
+    admin_library: ckeditor5/internal.admin.essentials
     elements:
       - <p>
 
@@ -48,8 +48,8 @@ ckeditor5_heading:
           - { model: 'heading6', view: 'h6', title: 'Heading 6', class: 'ck-heading_heading6' }
   drupal:
     label: Headings
-    library: core/ckeditor5.internal
-    admin_library: ckeditor5/admin.heading
+    library: core/ckeditor5.essentials
+    admin_library: ckeditor5/internal.admin.heading
     class: Drupal\ckeditor5\Plugin\CKEditor5Plugin\Heading
     toolbar_items:
       heading:
@@ -68,7 +68,7 @@ ckeditor5_style:
   drupal:
     label: Style
     library: core/ckeditor5.style
-    admin_library: ckeditor5/admin.style
+    admin_library: ckeditor5/internal.admin.style
     class: Drupal\ckeditor5\Plugin\CKEditor5Plugin\Style
     toolbar_items:
       style:
@@ -168,7 +168,7 @@ ckeditor5_specialCharacters:
   drupal:
     label: Special characters
     library: core/ckeditor5.specialCharacters
-    admin_library: ckeditor5/admin.specialCharacters
+    admin_library: ckeditor5/internal.admin.specialCharacters
     toolbar_items:
       specialCharacters:
         label: Special characters
@@ -188,7 +188,7 @@ ckeditor5_sourceEditing:
     # @see \Drupal\ckeditor5\Plugin\CKEditor5PluginManager::getProvidedElements()
     elements: []
     library: core/ckeditor5.sourceEditing
-    admin_library: ckeditor5/admin.sourceEditing
+    admin_library: ckeditor5/internal.admin.sourceEditing
     toolbar_items:
       sourceEditing:
         label: Source
@@ -199,7 +199,7 @@ ckeditor5_bold:
   drupal:
     label: Bold
     library: core/ckeditor5.basic
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     toolbar_items:
       bold:
         label: Bold
@@ -213,8 +213,8 @@ ckeditor5_emphasis:
       - drupalEmphasis.DrupalEmphasis
   drupal:
     label: Emphasis
-    library: ckeditor5/drupal.ckeditor5.emphasis
-    admin_library: ckeditor5/admin.basic
+    library: ckeditor5/internal.drupal.ckeditor5.emphasis
+    admin_library: ckeditor5/internal.admin.basic
     toolbar_items:
       italic:
         label: Italic
@@ -227,7 +227,7 @@ ckeditor5_underline:
   drupal:
     label: Underline
     library: core/ckeditor5.basic
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     toolbar_items:
       underline:
         label: Underline
@@ -240,7 +240,7 @@ ckeditor5_code:
   drupal:
     label: Code
     library: core/ckeditor5.basic
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     toolbar_items:
       code:
         label: Code
@@ -261,8 +261,8 @@ ckeditor5_codeBlock:
             name: pre
   drupal:
     label: Code Block
-    library: ckeditor5/drupal.ckeditor5.codeBlock
-    admin_library: ckeditor5/admin.codeBlock
+    library: ckeditor5/internal.drupal.ckeditor5.codeBlock
+    admin_library: ckeditor5/internal.admin.codeBlock
     toolbar_items:
       codeBlock:
         label: Code Block
@@ -277,7 +277,7 @@ ckeditor5_strikethrough:
   drupal:
     label: Strikethrough
     library: core/ckeditor5.basic
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     toolbar_items:
       strikethrough:
         label: Strikethrough
@@ -290,7 +290,7 @@ ckeditor5_subscript:
   drupal:
     label: Subscript
     library: core/ckeditor5.basic
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     toolbar_items:
       subscript:
         label: Subscript
@@ -303,7 +303,7 @@ ckeditor5_superscript:
   drupal:
     label: Superscript
     library: core/ckeditor5.basic
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     toolbar_items:
       superscript:
         label: Superscript
@@ -317,7 +317,7 @@ ckeditor5_blockquote:
   drupal:
     label: Block quote
     library: core/ckeditor5.blockquote
-    admin_library: ckeditor5/admin.blockquote
+    admin_library: ckeditor5/internal.admin.blockquote
     toolbar_items:
       blockQuote:
         label: Block quote
@@ -331,7 +331,7 @@ ckeditor5_link:
   drupal:
     label: Link
     library: core/ckeditor5.link
-    admin_library: ckeditor5/admin.link
+    admin_library: ckeditor5/internal.admin.link
     toolbar_items:
       link:
         label: Link
@@ -388,7 +388,7 @@ ckeditor5_list:
   drupal:
     label: List
     library: core/ckeditor5.list
-    admin_library: ckeditor5/admin.list
+    admin_library: ckeditor5/internal.admin.list
     class: Drupal\ckeditor5\Plugin\CKEditor5Plugin\ListPlugin
     toolbar_items:
       bulletedList:
@@ -407,7 +407,7 @@ ckeditor5_horizontalLine:
   drupal:
     label: Horizontal line
     library: core/ckeditor5.horizontalLine
-    admin_library: ckeditor5/admin.horizontalLine
+    admin_library: ckeditor5/internal.admin.horizontalLine
     toolbar_items:
       horizontalLine:
         label: Horizontal line
@@ -432,7 +432,7 @@ ckeditor5_alignment:
   drupal:
     label: Alignment
     library: core/ckeditor5.alignment
-    admin_library: ckeditor5/admin.alignment
+    admin_library: ckeditor5/internal.admin.alignment
     class: Drupal\ckeditor5\Plugin\CKEditor5Plugin\Alignment
     toolbar_items:
       alignment:
@@ -446,7 +446,7 @@ ckeditor5_removeFormat:
   drupal:
     label: Remove Format
     library: core/ckeditor5.removeFormat
-    admin_library: ckeditor5/admin.removeFormat
+    admin_library: ckeditor5/internal.admin.removeFormat
     toolbar_items:
       removeFormat:
         label: Remove Format
@@ -474,7 +474,7 @@ ckeditor5_table:
   drupal:
     label: Table
     library: core/ckeditor5.table
-    admin_library: ckeditor5/admin.table
+    admin_library: ckeditor5/internal.admin.table
     toolbar_items:
       insertTable:
         label: table
@@ -503,8 +503,8 @@ ckeditor5_image:
   drupal:
     label: Image
     class: \Drupal\ckeditor5\Plugin\CKEditor5Plugin\Image
-    library: ckeditor5/drupal.ckeditor5.image
-    admin_library: ckeditor5/admin.image
+    library: ckeditor5/internal.drupal.ckeditor5.image
+    admin_library: ckeditor5/internal.admin.image
     elements:
       - <img>
       - <img src alt height width>
@@ -619,7 +619,7 @@ ckeditor5_indent:
     label: Indent
     elements: false
     library: core/ckeditor5.indent
-    admin_library: ckeditor5/admin.indent
+    admin_library: ckeditor5/internal.admin.indent
     toolbar_items:
       indent:
         label: Indent
@@ -631,8 +631,8 @@ ckeditor5_language:
     plugins: [language.TextPartLanguage]
   drupal:
     label: Language
-    library: ckeditor5/ckeditor5.language
-    admin_library: ckeditor5/admin.language
+    library: ckeditor5/internal.ckeditor5.language
+    admin_library: ckeditor5/internal.admin.language
     class: Drupal\ckeditor5\Plugin\CKEditor5Plugin\Language
     toolbar_items:
       textPartLanguage:
@@ -656,7 +656,7 @@ media_media:
             invoke: true
   drupal:
     label: Media
-    library: ckeditor5/drupal.ckeditor5.media
+    library: ckeditor5/internal.drupal.ckeditor5.media
     class: Drupal\ckeditor5\Plugin\CKEditor5Plugin\Media
     elements:
       - <drupal-media>
@@ -722,7 +722,7 @@ media_mediaAlign:
           - '|'
   drupal:
     label: Media align
-    library: ckeditor5/drupal.ckeditor5.mediaAlign
+    library: ckeditor5/internal.drupal.ckeditor5.mediaAlign
     elements:
       - <drupal-media data-align>
     conditions:
@@ -746,7 +746,7 @@ media_library_mediaLibrary:
   drupal:
     label: Media Library
     elements: false
-    admin_library: ckeditor5/admin.drupalmedia
+    admin_library: ckeditor5/internal.admin.drupalmedia
     class: Drupal\ckeditor5\Plugin\CKEditor5Plugin\MediaLibrary
     library: editor/drupal.editor.dialog
     toolbar_items:
diff --git a/core/modules/ckeditor5/ckeditor5.info.yml b/core/modules/ckeditor5/ckeditor5.info.yml
index 6d93d11a3fa0af0edb4dc9e7b2e37bc3da58900b..c092f73f583718e9b6e1739d364ef2a39f987e59 100644
--- a/core/modules/ckeditor5/ckeditor5.info.yml
+++ b/core/modules/ckeditor5/ckeditor5.info.yml
@@ -2,7 +2,6 @@ name: CKEditor 5
 type: module
 description: "WYSIWYG editing for rich text fields using CKEditor 5."
 version: VERSION
-package: Core (Experimental)
-lifecycle: experimental
+package: Core
 dependencies:
   - drupal:editor
diff --git a/core/modules/ckeditor5/ckeditor5.libraries.yml b/core/modules/ckeditor5/ckeditor5.libraries.yml
index 5aea84a45c4531a054d3abe4d62c4b4d2af82939..a42b9434950c78c03e81b8aae87831b168c69bfd 100644
--- a/core/modules/ckeditor5/ckeditor5.libraries.yml
+++ b/core/modules/ckeditor5/ckeditor5.libraries.yml
@@ -1,18 +1,28 @@
-ckeditor5.language:
+# Internal libraries, do not depend on these.
+# CKEditor 5 has a much faster release cadence for major and minor releases
+# than Drupal. CKEditor 5 does not provide continued support for major or
+# minor releases; they almost never issue patch releases. Drupal therefore
+# has to keep its integration up-to-date with upstream. It is hence
+# impossible to provide "stable overrides", since the stability is not
+# controlled by Drupal, but by upstream.
+# Hence all CKEditor 5 asset libraries are considered internal.
+# @see https://ckeditor.com/docs/ckeditor5/latest/support/versioning-policy.html
+
+internal.ckeditor5.language:
   css:
     component:
       css/language.css: {}
   dependencies:
     - core/ckeditor5.language
 
-drupal.ckeditor5.internal:
+internal.drupal.ckeditor5.htmlEngine:
   js:
     js/build/drupalHtmlEngine.js: { minified: true }
   dependencies:
     - core/ckeditor5
-    - core/ckeditor5.internal
+    - core/ckeditor5.essentials
 
-drupal.ckeditor5:
+internal.drupal.ckeditor5:
   js:
     js/ckeditor5.js: {}
   css:
@@ -27,23 +37,23 @@ drupal.ckeditor5:
     - core/ckeditor5.editorDecoupled
     - core/ckeditor5
     - editor/drupal.editor
-    - ckeditor5/drupal.ckeditor5.stylesheets
+    - ckeditor5/internal.drupal.ckeditor5.stylesheets
     - core/drupalSettings
     - core/drupal.message
 
 # Library used for dynamically loading CKEditor 5 stylesheets from the default
 # front end theme.
 # @see ckeditor5_library_info_alter()
-drupal.ckeditor5.stylesheets:
+internal.drupal.ckeditor5.stylesheets:
   version: VERSION
   css: []
 
-drupal.ckeditor5.codeBlock:
+internal.drupal.ckeditor5.codeBlock:
   dependencies:
     - core/ckeditor5.codeBlock
     - core/ckeditor5.htmlSupport
 
-drupal.ckeditor5.image:
+internal.drupal.ckeditor5.image:
   js:
     js/build/drupalImage.js: { minified: true }
   css:
@@ -54,7 +64,7 @@ drupal.ckeditor5.image:
     - core/ckeditor5
     - core/ckeditor5.image
 
-drupal.ckeditor5.emphasis:
+internal.drupal.ckeditor5.emphasis:
   version: VERSION
   js:
     js/build/drupalEmphasis.js: { minified: true }
@@ -62,7 +72,7 @@ drupal.ckeditor5.emphasis:
     - core/ckeditor5
     - core/ckeditor5.basic
 
-drupal.ckeditor5.media:
+internal.drupal.ckeditor5.media:
   js:
     js/build/drupalMedia.js: { minified: true }
   css:
@@ -73,14 +83,14 @@ drupal.ckeditor5.media:
     - core/drupal
     - media/media_embed_ckeditor_theme
 
-drupal.ckeditor5.mediaAlign:
+internal.drupal.ckeditor5.mediaAlign:
   css:
     theme:
       css/media-alignment.css: { }
   dependencies:
-    - ckeditor5/drupal.ckeditor5.media
+    - ckeditor5/internal.drupal.ckeditor5.media
 
-drupal.ckeditor5.filter.admin:
+internal.drupal.ckeditor5.filter.admin:
   js:
     js/ckeditor5.filter.admin.js: {}
   dependencies:
@@ -89,7 +99,7 @@ drupal.ckeditor5.filter.admin:
     - core/drupal.ajax
     - core/drupalSettings
 
-admin:
+internal.admin:
   js:
     js/ckeditor5.admin.js: { }
   css:
@@ -101,79 +111,79 @@ admin:
     - core/jquery
     - core/once
 
-admin.specialCharacters:
+internal.admin.specialCharacters:
   css:
     theme:
       css/special-characters.css: { }
 
-admin.removeFormat:
+internal.admin.removeFormat:
   css:
     theme:
       css/remove-format.css: { }
 
-admin.internal:
+internal.admin.essentials:
   css:
     theme:
-      css/internal.admin.css: { }
+      css/essentials.admin.css: { }
 
-admin.basic:
+internal.admin.basic:
   css:
     theme:
       css/basic.admin.css: { }
 
-admin.blockquote:
+internal.admin.blockquote:
   css:
     theme:
       css/blockquote.admin.css: { }
 
-admin.link:
+internal.admin.link:
   css:
     theme:
       css/link.admin.css: { }
 
-admin.list:
+internal.admin.list:
   css:
     theme:
       css/list.admin.css: { }
 
-admin.heading:
+internal.admin.heading:
   css:
     theme:
       css/heading.admin.css: { }
   dependencies:
-    - core/ckeditor5.internal
+    - core/ckeditor5.essentials
 
-admin.horizontalLine:
+internal.admin.horizontalLine:
   css:
     theme:
       css/horizontal-line.admin.css: { }
 
-admin.alignment:
+internal.admin.alignment:
   css:
     theme:
       css/alignment.admin.css: { }
 
-admin.indent:
+internal.admin.indent:
   css:
     theme:
       css/indent.admin.css: { }
 
-admin.language:
+internal.admin.language:
   css:
     theme:
       css/language.admin.css: { }
 
-admin.drupalmedia:
+internal.admin.drupalmedia:
   css:
     theme:
       css/drupalmedia.admin.css: { }
 
-admin.sourceEditing:
+internal.admin.sourceEditing:
   css:
     theme:
       css/source-editing.admin.css: { }
 
-admin.style:
+internal.admin.style:
   js:
     js/ckeditor5.style.admin.js: { }
   css:
@@ -184,17 +194,17 @@ admin.style:
     - core/drupal
     - core/drupal.vertical-tabs
 
-admin.table:
+internal.admin.table:
   css:
     theme:
       css/table.admin.css: { }
 
-admin.codeBlock:
+internal.admin.codeBlock:
   css:
     theme:
       css/code-block.admin.css: { }
 
-admin.image:
+internal.admin.image:
   css:
     theme:
       css/image.admin.css: { }
diff --git a/core/modules/ckeditor5/ckeditor5.module b/core/modules/ckeditor5/ckeditor5.module
index f1472d0e17eebbea6f54cf365d17b28e3146c233..8b169fcfe66529486fa86454e5b7dc34cae7f6fc 100644
--- a/core/modules/ckeditor5/ckeditor5.module
+++ b/core/modules/ckeditor5/ckeditor5.module
@@ -423,7 +423,7 @@ function _ckeditor5_get_langcode_mapping($lang = FALSE) {
  */
 function ckeditor5_library_info_alter(&$libraries, $extension) {
   if ($extension === 'filter') {
-    $libraries['drupal.filter.admin']['dependencies'][] = 'ckeditor5/drupal.ckeditor5.filter.admin';
+    $libraries['drupal.filter.admin']['dependencies'][] = 'ckeditor5/internal.drupal.ckeditor5.filter.admin';
   }
 
   $moduleHandler = \Drupal::moduleHandler();
@@ -432,7 +432,7 @@ function ckeditor5_library_info_alter(&$libraries, $extension) {
     // Add paths to stylesheets specified by a theme's ckeditor5-stylesheets
     // config property.
     $css = _ckeditor5_theme_css();
-    $libraries['drupal.ckeditor5.stylesheets'] = [
+    $libraries['internal.drupal.ckeditor5.stylesheets'] = [
       'css' => [
         'theme' => array_fill_keys(array_values($css), []),
       ],
diff --git a/core/modules/ckeditor5/css/internal.admin.css b/core/modules/ckeditor5/css/essentials.admin.css
similarity index 100%
rename from core/modules/ckeditor5/css/internal.admin.css
rename to core/modules/ckeditor5/css/essentials.admin.css
diff --git a/core/modules/ckeditor5/src/Plugin/CKEditor5PluginManager.php b/core/modules/ckeditor5/src/Plugin/CKEditor5PluginManager.php
index a5f58e55cb336fdf9b26ca6d0031cbe783f932c5..068647a0bc7b59139947247c24aee02b3887e923 100644
--- a/core/modules/ckeditor5/src/Plugin/CKEditor5PluginManager.php
+++ b/core/modules/ckeditor5/src/Plugin/CKEditor5PluginManager.php
@@ -110,7 +110,7 @@ public function getToolbarItems(): array {
   public function getAdminLibraries(): array {
     $list = $this->mergeDefinitionValues('getAdminLibrary', $this->getDefinitions());
     // Include main admin library.
-    array_unshift($list, 'ckeditor5/admin');
+    array_unshift($list, 'ckeditor5/internal.admin');
     return $list;
   }
 
@@ -121,7 +121,7 @@ public function getEnabledLibraries(EditorInterface $editor): array {
     $list = $this->mergeDefinitionValues('getLibrary', $this->getEnabledDefinitions($editor));
     $list = array_unique($list);
     // Include main library.
-    array_unshift($list, 'ckeditor5/drupal.ckeditor5');
+    array_unshift($list, 'ckeditor5/internal.drupal.ckeditor5');
     sort($list);
     return $list;
   }
diff --git a/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php b/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php
index ace2815ee370b5e80fb113a5bb698b7606fea9a7..aa5d2661668a1ca03d75be766a3cd37e86c5f18f 100644
--- a/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php
+++ b/core/modules/ckeditor5/tests/src/Kernel/CKEditor5PluginManagerTest.php
@@ -332,7 +332,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
 YAML,
       NULL,
     ];
@@ -348,7 +348,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions:
       foo: bar
 YAML,
@@ -364,7 +364,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions:
       toolbarItem: [bold, italic]
 YAML,
@@ -380,7 +380,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions:
       toolbarItem: bold
 YAML,
@@ -396,7 +396,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions:
       toolbarItem: bold
       filter: true
@@ -413,7 +413,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions:
       toolbarItem: bold
       filter: filter_caption
@@ -430,7 +430,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions:
       toolbarItem: bold
       filter: filter_caption
@@ -448,7 +448,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions:
       toolbarItem: bold
       filter: filter_caption
@@ -466,7 +466,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions:
       toolbarItem: bold
       filter: filter_caption
@@ -485,7 +485,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions:
       toolbarItem: bold
       filter: filter_caption
@@ -504,7 +504,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions: []
 YAML,
       NULL,
@@ -519,7 +519,7 @@ public function providerTestInvalidPluginDefinitions(): \Generator {
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
     conditions: false
 YAML,
       NULL,
@@ -537,7 +537,7 @@ class: Drupal\ckeditor5_invalid_plugin\Plugin\CKEditor5Plugin\FooBar
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
 YAML,
       'The CKEditor 5 "ckeditor5_invalid_plugin_foo_bar" provides a plugin class: "Drupal\ckeditor5_invalid_plugin\Plugin\CKEditor5Plugin\FooBar", but it does not exist.',
     ];
@@ -553,7 +553,7 @@ class: Drupal\ckeditor5_invalid_plugin\Plugin\CKEditor5Plugin\FooBar
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
 YAML,
       'CKEditor 5 plugins must implement \Drupal\ckeditor5\Plugin\CKEditor5PluginInterface. "ckeditor5_invalid_plugin_foo_bar" does not.',
       [
@@ -582,7 +582,7 @@ class: Drupal\ckeditor5_invalid_plugin\Plugin\CKEditor5Plugin\FooBar
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
 YAML,
       NULL,
       [
@@ -614,7 +614,7 @@ class: Drupal\ckeditor5_invalid_plugin\Plugin\CKEditor5Plugin\FooBar
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
 YAML,
       NULL,
       [
@@ -653,7 +653,7 @@ class: Drupal\ckeditor5_invalid_plugin\Plugin\CKEditor5Plugin\FooBar
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
 YAML,
       'The "ckeditor5_invalid_plugin_foo_bar" CKEditor 5 plugin definition is configurable, has non-empty default configuration but has no config schema. Config schema is required for validation.',
       [
@@ -692,7 +692,7 @@ class: Drupal\ckeditor5_invalid_plugin\Plugin\CKEditor5Plugin\FooBar
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
 YAML,
       NULL,
       [
@@ -744,7 +744,7 @@ class: Drupal\ckeditor5_invalid_plugin\Plugin\CKEditor5Plugin\FooBar
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
 YAML,
       'The "ckeditor5_invalid_plugin_foo_bar" CKEditor 5 plugin definition is configurable, but its default configuration does not match its config schema. The following errors were found: [foo] The configuration property foo.bar doesn\'t exist, [baz] missing schema.',
       [
@@ -796,7 +796,7 @@ class: Drupal\ckeditor5_invalid_plugin\Plugin\CKEditor5Plugin\FooBar
     elements:
       - <foo>
       - <bar>
-    admin_library: ckeditor5/admin.basic
+    admin_library: ckeditor5/internal.admin.basic
 YAML,
       NULL,
       [
@@ -1058,12 +1058,12 @@ public function testEnabledPlugins() {
     ];
     $this->assertSame($default_plugins, $definitions, 'No CKEditor 5 plugins found besides the built-in ones.');
     $default_libraries = [
-      'ckeditor5/drupal.ckeditor5',
-      'ckeditor5/drupal.ckeditor5.emphasis',
-      'ckeditor5/drupal.ckeditor5.internal',
+      'ckeditor5/internal.drupal.ckeditor5',
+      'ckeditor5/internal.drupal.ckeditor5.emphasis',
+      'ckeditor5/internal.drupal.ckeditor5.htmlEngine',
       'core/ckeditor5.basic',
+      'core/ckeditor5.essentials',
       'core/ckeditor5.htmlSupport',
-      'core/ckeditor5.internal',
       'core/ckeditor5.pasteFromOffice',
     ];
     $this->assertSame($default_libraries, $this->manager->getEnabledLibraries($editor));
@@ -1109,8 +1109,8 @@ public function testEnabledPlugins() {
     sort($expected_plugins);
     $this->assertSame($expected_plugins, $plugin_ids);
     $expected_libraries = array_merge($default_libraries, [
-      'ckeditor5/drupal.ckeditor5.media',
-      'ckeditor5/drupal.ckeditor5.mediaAlign',
+      'ckeditor5/internal.drupal.ckeditor5.media',
+      'ckeditor5/internal.drupal.ckeditor5.mediaAlign',
       'ckeditor5_test/layercake',
     ]);
     sort($expected_libraries);
@@ -1138,8 +1138,8 @@ public function testEnabledPlugins() {
     sort($expected_plugins);
     $this->assertSame(array_values($expected_plugins), $plugin_ids);
     $expected_libraries = array_merge($default_libraries, [
-      'ckeditor5/drupal.ckeditor5.media',
-      'ckeditor5/drupal.ckeditor5.mediaAlign',
+      'ckeditor5/internal.drupal.ckeditor5.media',
+      'ckeditor5/internal.drupal.ckeditor5.mediaAlign',
       'ckeditor5_test/layercake',
       'core/ckeditor5.table',
     ]);
@@ -1178,12 +1178,12 @@ public function testEnabledPlugins() {
     ];
     $this->assertSame($default_plugins, $definitions, 'No CKEditor 5 plugins found besides the built-in ones.');
     $default_libraries = [
-      'ckeditor5/drupal.ckeditor5',
-      'ckeditor5/drupal.ckeditor5.emphasis',
-      'ckeditor5/drupal.ckeditor5.internal',
+      'ckeditor5/internal.drupal.ckeditor5',
+      'ckeditor5/internal.drupal.ckeditor5.emphasis',
+      'ckeditor5/internal.drupal.ckeditor5.htmlEngine',
       'core/ckeditor5.basic',
+      'core/ckeditor5.essentials',
       'core/ckeditor5.htmlSupport',
-      'core/ckeditor5.internal',
       'core/ckeditor5.pasteFromOffice',
     ];
     $this->assertSame($default_libraries, $this->manager->getEnabledLibraries($editor));
diff --git a/core/tests/Drupal/KernelTests/Core/Theme/Stable9LibraryOverrideTest.php b/core/tests/Drupal/KernelTests/Core/Theme/Stable9LibraryOverrideTest.php
index 855fd0347ff93d3f4926444271d028ebe7de067d..e140b481c4eebc8ee2c87d4bedd1d5d25c8c2076 100644
--- a/core/tests/Drupal/KernelTests/Core/Theme/Stable9LibraryOverrideTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Theme/Stable9LibraryOverrideTest.php
@@ -62,6 +62,10 @@ public function testStable9LibraryOverrides() {
         if (in_array("$extension/$library_name", $this->librariesToSkip)) {
           continue;
         }
+        // Skip internal libraries.
+        if (substr($library_name, 0, 9) === 'internal.') {
+          continue;
+        }
         $library_after = $libraries_after[$extension][$library_name];
 
         // Check that all the CSS assets are overridden.
diff --git a/core/tests/Drupal/KernelTests/Core/Theme/Stable9TemplateOverrideTest.php b/core/tests/Drupal/KernelTests/Core/Theme/Stable9TemplateOverrideTest.php
index 486fe12e646e55a9ee1f2b4363bf63b184a9288d..afc1105cb485e50e5e05fda01a26784ce96ac346 100644
--- a/core/tests/Drupal/KernelTests/Core/Theme/Stable9TemplateOverrideTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Theme/Stable9TemplateOverrideTest.php
@@ -24,6 +24,8 @@ class Stable9TemplateOverrideTest extends KernelTestBase {
    * @var string[]
    */
   protected $templatesToSkip = [
+    // This is an internal template. See the file docblock.
+    'ckeditor5-settings-toolbar',
     // Registered as a template in the views_theme() function in views.module
     // but an actual template does not exist.
     'views-form-views-form',
diff --git a/core/tests/Drupal/KernelTests/Core/Theme/StableLibraryOverrideTest.php b/core/tests/Drupal/KernelTests/Core/Theme/StableLibraryOverrideTest.php
index 30c9c27ce4c6fdd1e306c60a1ebed2d13dab4956..45831f32c35f3bd3b1ba1ad418bab87ab28a5906 100644
--- a/core/tests/Drupal/KernelTests/Core/Theme/StableLibraryOverrideTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Theme/StableLibraryOverrideTest.php
@@ -90,6 +90,10 @@ public function testStableLibraryOverrides() {
         if (in_array("$extension/$library_name", $this->librariesToSkip)) {
           continue;
         }
+        // Skip internal libraries.
+        if (substr($library_name, 0, 9) === 'internal.') {
+          continue;
+        }
         $library_after = $libraries_after[$extension][$library_name];
 
         // Check that all the CSS assets are overridden.
diff --git a/core/tests/Drupal/KernelTests/Core/Theme/StableTemplateOverrideTest.php b/core/tests/Drupal/KernelTests/Core/Theme/StableTemplateOverrideTest.php
index 1dd98306f2cbcd304d6b5988026d62bec6d81473..52587cceafd34a875573d6d0f560130ffb2fcf7d 100644
--- a/core/tests/Drupal/KernelTests/Core/Theme/StableTemplateOverrideTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Theme/StableTemplateOverrideTest.php
@@ -24,6 +24,10 @@ class StableTemplateOverrideTest extends KernelTestBase {
    * @var string[]
    */
   protected $templatesToSkip = [
+    // This is an internal template. See the file docblock.
+    'ckeditor5-settings-toolbar',
+    // Registered as a template in the views_theme() function in views.module
+    // but an actual template does not exist.
     'views-form-views-form',
     'views-view-grid-responsive',
   ];