diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
index 6d654d8509..74a87cd403 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view.ts
@@ -367,13 +367,6 @@ export class GrChangeView extends KeyboardShortcutMixin(
   })
   _hideEditCommitMessage?: boolean;
 
-  @property({
-    type: Boolean,
-    computed:
-      '_computeHideShowAllContainer(_hideEditCommitMessage, _commitCollapsible)',
-  })
-  _hideShowAllContainer = false;
-
   @property({type: String})
   _diffAgainst?: string;
 
@@ -918,13 +911,6 @@ export class GrChangeView extends KeyboardShortcutMixin(
     return changeStatuses(change, options);
   }
 
-  _computeHideShowAllContainer(
-    _hideEditCommitMessage?: boolean,
-    _commitCollapsible?: boolean
-  ) {
-    return !_commitCollapsible && _hideEditCommitMessage;
-  }
-
   _computeHideEditCommitMessage(
     loggedIn: boolean,
     editing: boolean,
@@ -2363,6 +2349,9 @@ export class GrChangeView extends KeyboardShortcutMixin(
   }
 
   _computeCommitMessageCollapsed(collapsed?: boolean, collapsible?: boolean) {
+    if (this._isNewChangeSummaryUiEnabled) {
+      return false;
+    }
     return collapsible && collapsed;
   }
 
@@ -2371,9 +2360,6 @@ export class GrChangeView extends KeyboardShortcutMixin(
   }
 
   _computeCollapseText(collapsed: boolean) {
-    if (this._isNewChangeSummaryUiEnabled) {
-      return collapsed ? 'Show all' : 'Show less';
-    }
     // Symbols are up and down triangles.
     return collapsed ? '\u25bc Show more' : '\u25b2 Show less';
   }
diff --git a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts
index 36e73b2ed1..2be7173a4d 100644
--- a/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts
+++ b/polygerrit-ui/app/elements/change/gr-change-view/gr-change-view_html.ts
@@ -109,25 +109,6 @@ export const htmlTemplate = html`
       /* Account for border and padding and rounding errors. */
       max-width: calc(72ch + 2px + 2 * var(--spacing-m) + 0.4px);
     }
-    .show-all-container {
-      background-color: var(--view-background-color);
-      display: flex;
-      justify-content: flex-end;
-      margin-bottom: 8px;
-      border-top-width: 1px;
-      border-top-style: solid;
-      border-radius: 0 0 4px 4px;
-      border-color: var(--border-color);
-      box-shadow: var(--elevation-level-1);
-    }
-    .show-all-container .show-all-button {
-      margin-right: auto;
-    }
-    .show-all-container iron-icon {
-      color: inherit;
-      --iron-icon-height: 18px;
-      --iron-icon-width: 18px;
-    }
     .commitMessage gr-linked-text {
       word-break: break-word;
     }
@@ -139,9 +120,6 @@ export const htmlTemplate = html`
     .new-change-summary-true #commitMessageEditor {
       --collapsed-max-height: 300px;
     }
-    .new-change-summary-true gr-linked-text {
-      min-height: 160px;
-    }
     .editCommitMessage {
       margin-top: var(--spacing-l);
 
@@ -492,9 +470,11 @@ export const htmlTemplate = html`
               >
                 <gr-editable-content
                   id="commitMessageEditor"
-                  editing="[[_editingCommitMessage]]"
+                  editing="{{_editingCommitMessage}}"
                   content="{{_latestCommitMessage}}"
                   storage-key="[[_computeCommitMessageKey(_change._number, _change.current_revision)]]"
+                  hide-edit-commit-message="[[_hideEditCommitMessage]]"
+                  commit-collapsible="[[_commitCollapsible]]"
                   remove-zero-width-space=""
                   collapsed$="[[_computeCommitMessageCollapsed(_commitCollapsed, _commitCollapsible)]]"
                 >
@@ -505,37 +485,6 @@ export const htmlTemplate = html`
                     remove-zero-width-space=""
                   ></gr-linked-text>
                 </gr-editable-content>
-                <template is="dom-if" if="[[_isNewChangeSummaryUiEnabled]]">
-                  <div
-                    class="show-all-container"
-                    hidden$="[[_hideShowAllContainer]]"
-                  >
-                    <gr-button
-                      link=""
-                      class="show-all-button"
-                      on-click="_toggleCommitCollapsed"
-                      hidden$="[[!_commitCollapsible]]"
-                      ><iron-icon
-                        icon="gr-icons:expand-more"
-                        hidden$="[[!_commitCollapsed]]"
-                      ></iron-icon
-                      ><iron-icon
-                        icon="gr-icons:expand-less"
-                        hidden$="[[_commitCollapsed]]"
-                      ></iron-icon>
-                      [[_computeCollapseText(_commitCollapsed)]]
-                    </gr-button>
-                    <gr-button
-                      link=""
-                      class="edit-commit-message"
-                      title="Edit commit message"
-                      on-click="_handleEditCommitMessage"
-                      hidden$="[[_hideEditCommitMessage]]"
-                      ><iron-icon icon="gr-icons:edit"></iron-icon>
-                      Edit</gr-button
-                    >
-                  </div>
-                </template>
                 <template is="dom-if" if="[[!_isNewChangeSummaryUiEnabled]]">
                   <gr-button
                     link=""
diff --git a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts
index 2537c1a29a..e825d210bc 100644
--- a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts
+++ b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content.ts
@@ -25,6 +25,8 @@ import {PolymerElement} from '@polymer/polymer/polymer-element';
 import {customElement, property} from '@polymer/decorators';
 import {htmlTemplate} from './gr-editable-content_html';
 import {fireAlert, fireEvent} from '../../../utils/event-util';
+import {appContext} from '../../../services/app-context';
+import {KnownExperimentId} from '../../../services/flags/flags';
 
 const RESTORED_MESSAGE = 'Content restored from a previous edit.';
 const STORAGE_DEBOUNCE_INTERVAL_MS = 400;
@@ -67,7 +69,7 @@ export class GrEditableContent extends GestureEventListeners(
   @property({type: Boolean, reflectToAttribute: true})
   disabled = false;
 
-  @property({type: Boolean, observer: '_editingChanged'})
+  @property({type: Boolean, observer: '_editingChanged', notify: true})
   editing = false;
 
   @property({type: Boolean})
@@ -77,6 +79,29 @@ export class GrEditableContent extends GestureEventListeners(
   @property({type: String})
   storageKey?: string;
 
+  /** If false, then the "Show more" button was used to expand. */
+  @property({type: Boolean})
+  _commitCollapsed = true;
+
+  @property({type: Boolean})
+  commitCollapsible = true;
+
+  @property({
+    type: Boolean,
+    computed:
+      '_computeHideShowAllContainer(hideEditCommitMessage, _hideShowAllButton, editing)',
+  })
+  _hideShowAllContainer = false;
+
+  @property({
+    type: Boolean,
+    computed: '_computeHideShowAllButton(commitCollapsible, editing)',
+  })
+  _hideShowAllButton = false;
+
+  @property({type: Boolean})
+  hideEditCommitMessage?: boolean;
+
   @property({
     type: Boolean,
     computed: '_computeSaveDisabled(disabled, content, _newContent)',
@@ -86,8 +111,21 @@ export class GrEditableContent extends GestureEventListeners(
   @property({type: String, observer: '_newContentChanged'})
   _newContent?: string;
 
+  @property({type: Boolean})
+  _isNewChangeSummaryUiEnabled = false;
+
   private readonly storage = new GrStorage();
 
+  private readonly flagsService = appContext.flagsService;
+
+  /** @override */
+  ready() {
+    super.ready();
+    this._isNewChangeSummaryUiEnabled = this.flagsService.isEnabled(
+      KnownExperimentId.NEW_CHANGE_SUMMARY_UI
+    );
+  }
+
   _contentChanged() {
     /* A changed content means that either a different change has been loaded
      * or new content was saved. Either way, let's reset the component.
@@ -186,4 +224,37 @@ export class GrEditableContent extends GestureEventListeners(
     this.editing = false;
     fireEvent(this, 'editable-content-cancel');
   }
+
+  _computeCollapseText(collapsed: boolean) {
+    return collapsed ? 'Show all' : 'Show less';
+  }
+
+  _toggleCommitCollapsed() {
+    this._commitCollapsed = !this._commitCollapsed;
+    if (this._commitCollapsed) {
+      window.scrollTo(0, 0);
+    }
+  }
+
+  _computeHideShowAllContainer(
+    hideEditCommitMessage?: boolean,
+    _hideShowAllButton?: boolean,
+    editing?: boolean
+  ) {
+    if (editing) return false;
+    return _hideShowAllButton && hideEditCommitMessage;
+  }
+
+  _computeHideShowAllButton(commitCollapsible?: boolean, editing?: boolean) {
+    return !commitCollapsible || editing;
+  }
+
+  _computeCommitMessageCollapsed(collapsed?: boolean, collapsible?: boolean) {
+    return collapsible && collapsed;
+  }
+
+  _handleEditCommitMessage() {
+    this.editing = true;
+    this.focusTextarea();
+  }
 }
diff --git a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_html.ts b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_html.ts
index fa18761499..660539481a 100644
--- a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_html.ts
+++ b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_html.ts
@@ -31,13 +31,19 @@ export const htmlTemplate = html`
       box-shadow: var(--elevation-level-1);
       padding: var(--spacing-m);
     }
-    :host([collapsed]) .viewer {
+    :host([collapsed]) .viewer,
+    .viewer[collapsed] {
       max-height: var(--collapsed-max-height, 300px);
       overflow: hidden;
     }
+    .editor.new-change-summary-true iron-autogrow-textarea,
+    .viewer.new-change-summary-true {
+      min-height: 160px;
+    }
     .editor iron-autogrow-textarea {
       background-color: var(--view-background-color);
       width: 100%;
+      display: block;
 
       /* You have to also repeat everything from shared-styles here, because
            you can only *replace* --iron-autogrow-textarea vars as a whole. */
@@ -52,23 +58,103 @@ export const htmlTemplate = html`
       display: flex;
       justify-content: space-between;
     }
+    .show-all-container {
+      background-color: var(--view-background-color);
+      display: flex;
+      justify-content: flex-end;
+      margin-bottom: 8px;
+      border-top-width: 1px;
+      border-top-style: solid;
+      border-radius: 0 0 4px 4px;
+      border-color: var(--border-color);
+      box-shadow: var(--elevation-level-1);
+    }
+    .show-all-container .show-all-button {
+      margin-right: auto;
+    }
+    .show-all-container iron-icon {
+      color: inherit;
+      --iron-icon-height: 18px;
+      --iron-icon-width: 18px;
+    }
+    .cancel-button {
+      margin-right: var(--spacing-l);
+    }
+    .save-button {
+      margin-right: var(--spacing-xs);
+    }
   </style>
-  <div class="viewer" hidden$="[[editing]]">
+  <div
+    class$="viewer new-change-summary-[[_isNewChangeSummaryUiEnabled]]"
+    hidden$="[[editing]]"
+    collapsed$="[[_computeCommitMessageCollapsed(_commitCollapsed, commitCollapsible)]]"
+  >
     <slot></slot>
   </div>
-  <div class="editor" hidden$="[[!editing]]">
-    <iron-autogrow-textarea
-      autocomplete="on"
-      bind-value="{{_newContent}}"
-      disabled="[[disabled]]"
-    ></iron-autogrow-textarea>
-    <div class="editButtons">
-      <gr-button primary="" on-click="_handleSave" disabled="[[_saveDisabled]]"
-        >Save</gr-button
-      >
-      <gr-button on-click="_handleCancel" disabled="[[disabled]]"
-        >Cancel</gr-button
-      >
+  <div
+    class$="editor new-change-summary-[[_isNewChangeSummaryUiEnabled]]"
+    hidden$="[[!editing]]"
+  >
+    <div>
+      <iron-autogrow-textarea
+        autocomplete="on"
+        bind-value="{{_newContent}}"
+        disabled="[[disabled]]"
+      ></iron-autogrow-textarea>
+      <div class="editButtons" hidden$="[[_isNewChangeSummaryUiEnabled]]">
+        <gr-button
+          primary=""
+          on-click="_handleSave"
+          disabled="[[_saveDisabled]]"
+          >Save</gr-button
+        >
+        <gr-button on-click="_handleCancel" disabled="[[disabled]]"
+          >Cancel</gr-button
+        >
+      </div>
     </div>
   </div>
+  <template is="dom-if" if="[[_isNewChangeSummaryUiEnabled]]">
+    <div class="show-all-container" hidden$="[[_hideShowAllContainer]]">
+      <gr-button
+        link=""
+        class="show-all-button"
+        on-click="_toggleCommitCollapsed"
+        hidden$="[[_hideShowAllButton]]"
+        ><iron-icon
+          icon="gr-icons:expand-more"
+          hidden$="[[!_commitCollapsed]]"
+        ></iron-icon
+        ><iron-icon
+          icon="gr-icons:expand-less"
+          hidden$="[[_commitCollapsed]]"
+        ></iron-icon>
+        [[_computeCollapseText(_commitCollapsed)]]
+      </gr-button>
+      <gr-button
+        link=""
+        class="edit-commit-message"
+        title="Edit commit message"
+        on-click="_handleEditCommitMessage"
+        hidden$="[[hideEditCommitMessage]]"
+        ><iron-icon icon="gr-icons:edit"></iron-icon> Edit</gr-button
+      >
+      <div class="editButtons" hidden$="[[!editing]]">
+        <gr-button
+          link=""
+          class="cancel-button"
+          on-click="_handleCancel"
+          disabled="[[disabled]]"
+          >Cancel</gr-button
+        >
+        <gr-button
+          class="save-button"
+          primary=""
+          on-click="_handleSave"
+          disabled="[[_saveDisabled]]"
+          >Save</gr-button
+        >
+      </div>
+    </div>
+  </template>
 `;
diff --git a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_test.js b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_test.js
index a0481ae542..b99b11952e 100644
--- a/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_test.js
+++ b/polygerrit-ui/app/elements/shared/gr-editable-content/gr-editable-content_test.js
@@ -105,7 +105,7 @@ suite('gr-editable-content tests', () => {
 
       assert.equal(element._newContent, 'stored content');
       assert.isTrue(dispatchSpy.called);
-      assert.equal(dispatchSpy.lastCall.args[0].type, 'show-alert');
+      assert.equal(dispatchSpy.firstCall.args[0].type, 'show-alert');
     });
 
     test('editing toggled to true, has no stored data', () => {
@@ -114,7 +114,7 @@ suite('gr-editable-content tests', () => {
       element.editing = true;
 
       assert.equal(element._newContent, 'current content');
-      assert.isFalse(dispatchSpy.called);
+      assert.equal(dispatchSpy.firstCall.args[0].type, 'editing-changed');
     });
 
     test('edits are cached', () => {