diff --git a/client/dist/js/LeftAndMain_Subsites.js b/client/dist/js/LeftAndMain_Subsites.js
index 55de350a..4eb0d7a2 100644
--- a/client/dist/js/LeftAndMain_Subsites.js
+++ b/client/dist/js/LeftAndMain_Subsites.js
@@ -1 +1 @@
-!function(){"use strict";var t={669:function(t){t.exports=jQuery}},e={};var i,s=function i(s){var n=e[s];if(void 0!==n)return n.exports;var r=e[s]={exports:{}};return t[s](r,r.exports,i),r.exports}(669);(i=s).entwine("ss",(t=>{t("#SubsitesSelect").entwine({onadd(){this.on("change",(function(){window.location.search=t.query.set("SubsiteID",t(this).val())}))}}),t(".cms-container .cms-menu-list li a").entwine({onclick(e){t(".cms-container").loadFragment("admin/subsite_xhr","SubsiteList"),this._super(e)}}),t(".cms-container .SubsiteAdmin .cms-edit-form fieldset.ss-gridfield").entwine({onreload(e){t(".cms-container").loadFragment("admin/subsite_xhr","SubsiteList"),this._super(e)}}),t(".cms-container .tab.subsite-model").entwine({onadd(e){t(".cms-container").loadFragment("admin/subsite_xhr","SubsiteList"),this._super(e)}}),t("#Form_ItemEditForm_AccessAllSubsites").entwine({onmatch(){this.showHideSubsiteList();const e=this;t("#Form_ItemEditForm_AccessAllSubsites input").change((()=>{e.showHideSubsiteList()}))},showHideSubsiteList(){t("#Form_ItemEditForm_Subsites").parent().parent().css("display",t("#Form_ItemEditForm_AccessAllSubsites_1").is(":checked")?"none":"")}}),t(".cms-edit-form").entwine({getChangeTrackerOptions(){const e=void 0===this.entwineData("ChangeTrackerOptions");let i=this._super();return e&&(i=t.extend({},i),i.ignoreFieldSelector+=", input[name=IsSubsite]",this.setChangeTrackerOptions(i)),i}}),t(".cms-edit-form input[name=action_copytosubsite]").entwine({onclick(){this.closest("form").trigger("submit",[this])}})})),i.entwine("ss.preview",(t=>{t(".cms-preview").entwine({onafterIframeAdjustedForPreview(e,i){const s=t(i).find("meta[name=x-subsite-id]").attr("content");s&&(t(i).find("a").each((function(){const e=t(this).attr("href");void 0===e||e.match(/^http:\/\//)||t(this).attr("href",t.path.addSearchParams(e,{SubsiteID:s}))})),t(i).find("form").each((function(){const e=t(this).attr("action");void 0===e||e.match(/^http:\/\//)||t(this).append(`<input type=hidden name="SubsiteID" value="${s}" >`)})))}})}))}();
\ No newline at end of file
+!function(){"use strict";var t={669:function(t){t.exports=jQuery}},e={};var i,s=function i(s){var n=e[s];if(void 0!==n)return n.exports;var r=e[s]={exports:{}};return t[s](r,r.exports,i),r.exports}(669);(i=s).entwine("ss",(t=>{t("#SubsitesSelect").entwine({onadd(){this.on("change",(function(){window.location.search=t.query.set("SubsiteID",t(this).val())}))}}),t(".cms-container .SubsiteAdmin .cms-edit-form fieldset.ss-gridfield").entwine({onreload(e){t(".cms-container").loadFragment("admin/subsite_xhr","SubsiteList"),this._super(e)}}),t("#Form_ItemEditForm").entwine({onaftersubmitform(e){this.find('[role="tab"].subsite-model').length>0&&t(".cms-container").loadFragment("admin/subsite_xhr","SubsiteList"),this._super(e)}}),t("#Form_ItemEditForm_AccessAllSubsites").entwine({onmatch(){this.showHideSubsiteList();const e=this;t("#Form_ItemEditForm_AccessAllSubsites input").change((()=>{e.showHideSubsiteList()}))},showHideSubsiteList(){t("#Form_ItemEditForm_Subsites").parent().parent().css("display",t("#Form_ItemEditForm_AccessAllSubsites_1").is(":checked")?"none":"")}}),t(".cms-edit-form").entwine({getChangeTrackerOptions(){const e=void 0===this.entwineData("ChangeTrackerOptions");let i=this._super();return e&&(i=t.extend({},i),i.ignoreFieldSelector+=", input[name=IsSubsite]",this.setChangeTrackerOptions(i)),i}}),t(".cms-edit-form input[name=action_copytosubsite]").entwine({onclick(){this.closest("form").trigger("submit",[this])}})})),i.entwine("ss.preview",(t=>{t(".cms-preview").entwine({onafterIframeAdjustedForPreview(e,i){const s=t(i).find("meta[name=x-subsite-id]").attr("content");s&&(t(i).find("a").each((function(){const e=t(this).attr("href");void 0===e||e.match(/^http:\/\//)||t(this).attr("href",t.path.addSearchParams(e,{SubsiteID:s}))})),t(i).find("form").each((function(){const e=t(this).attr("action");void 0===e||e.match(/^http:\/\//)||t(this).append(`<input type=hidden name="SubsiteID" value="${s}" >`)})))}})}))}();
\ No newline at end of file
diff --git a/client/src/js/LeftAndMain_Subsites.js b/client/src/js/LeftAndMain_Subsites.js
index 3c8b6098..a3d44624 100644
--- a/client/src/js/LeftAndMain_Subsites.js
+++ b/client/src/js/LeftAndMain_Subsites.js
@@ -11,16 +11,6 @@
       }
     });
 
-    /*
-     * Reload subsites dropdown when links are processed
-     */
-    $('.cms-container .cms-menu-list li a').entwine({
-      onclick(e) {
-        $('.cms-container').loadFragment('admin/subsite_xhr', 'SubsiteList');
-        this._super(e);
-      }
-    });
-
     /*
      * Reload subsites dropdown when the admin area reloads (for deleting sites)
      */
@@ -32,11 +22,15 @@
     });
 
     /*
-     * Reload subsites dropdown when subsites are added or names are modified
+     * Reload subsites dropdown when subsites are added or modified
      */
-    $('.cms-container .tab.subsite-model').entwine({
-      onadd(e) {
-        $('.cms-container').loadFragment('admin/subsite_xhr', 'SubsiteList');
+    $('#Form_ItemEditForm').entwine({
+      onaftersubmitform(e) {
+        // Only load the fragment if this form is the subsite form.
+        // We can't add a selector to the form itself so check for the tab we added a specific class to.
+        if (this.find('[role="tab"].subsite-model').length > 0) {
+          $('.cms-container').loadFragment('admin/subsite_xhr', 'SubsiteList');
+        }
         this._super(e);
       }
     });
diff --git a/src/Controller/SubsiteXHRController.php b/src/Controller/SubsiteXHRController.php
index 04840749..57d1e0bf 100644
--- a/src/Controller/SubsiteXHRController.php
+++ b/src/Controller/SubsiteXHRController.php
@@ -2,21 +2,27 @@
 
 namespace SilverStripe\Subsites\Controller;
 
-use SilverStripe\Admin\LeftAndMain;
+use SilverStripe\Admin\AdminController;
+use SilverStripe\Control\HTTPRequest;
+use SilverStripe\Control\HTTPResponse;
 use SilverStripe\Control\PjaxResponseNegotiator;
-use SilverStripe\Dev\Deprecation;
+use SilverStripe\ORM\FieldType\DBHTMLText;
 use SilverStripe\Security\Member;
-use SilverStripe\Security\Permission;
 use SilverStripe\Subsites\Model\Subsite;
 
 /**
- * Section-agnostic PJAX controller.
+ * Section-agnostic PJAX controller that renders the subsites swapper dropdown
  */
-class SubsiteXHRController extends LeftAndMain
+class SubsiteXHRController extends AdminController
 {
     private static $url_segment = 'subsite_xhr';
 
-    private static $ignore_menuitem = true;
+    private static string $required_permission_codes = 'CMS_ACCESS';
+
+    public function index(HTTPRequest $request): HTTPResponse
+    {
+        return $this->getResponseNegotiator()->respond($request);
+    }
 
     /**
      * Relax the access permissions, so anyone who has access to any CMS subsite can access this controller.
@@ -37,35 +43,21 @@ public function canView($member = null)
     }
 
     /**
-     * Allow access if user allowed into the CMS at all.
-     * @deprecated 3.4.0 Will be removed without equivalent functionality to replace it.
+     * Get a Pjax response negotiator for the subsite list
      */
-    public function canAccess()
-    {
-        Deprecation::noticeWithNoReplacment('3.4.0');
-        // Allow if any cms access is available
-        return Permission::check([
-            'CMS_ACCESS', // Supported by 3.1.14 and up
-            'CMS_ACCESS_LeftAndMain'
-        ]);
-    }
-
     public function getResponseNegotiator(): PjaxResponseNegotiator
     {
-        $negotiator = parent::getResponseNegotiator();
-
-        // Register a new callback
-        $negotiator->setCallback('SubsiteList', function () {
-            return $this->SubsiteList();
-        });
-
-        return $negotiator;
+        return new PjaxResponseNegotiator([
+            'SubsiteList' => function () {
+                return $this->SubsiteList();
+            },
+        ]);
     }
 
     /**
      * Provide the list of available subsites as a cms-section-agnostic PJAX handler.
      */
-    public function SubsiteList()
+    public function SubsiteList(): DBHTMLText
     {
         return $this->renderWith(['type' => 'Includes', SubsiteXHRController::class . '_subsitelist']);
     }
diff --git a/src/Extensions/LeftAndMainSubsites.php b/src/Extensions/LeftAndMainSubsites.php
index 94a1b8a7..ae2e4fa7 100644
--- a/src/Extensions/LeftAndMainSubsites.php
+++ b/src/Extensions/LeftAndMainSubsites.php
@@ -13,7 +13,6 @@
 use SilverStripe\Core\Config\Config;
 use SilverStripe\Core\Convert;
 use SilverStripe\Core\Extension;
-use SilverStripe\Dev\Deprecation;
 use SilverStripe\Forms\HiddenField;
 use SilverStripe\Model\List\ArrayList;
 use SilverStripe\ORM\DataObject;
@@ -69,8 +68,6 @@ public static function SubsiteSwitchList(): SS_List
             return false;
         }
 
-        Requirements::javascript('silverstripe/subsites:client/dist/js/LeftAndMain_Subsites.js');
-
         $output = ArrayList::create();
 
         foreach ($list as $subsite) {
@@ -180,18 +177,6 @@ public function Subsites()
         return Subsite::all_accessible_sites();
     }
 
-    /**
-     * Generates a list of subsites with the data needed to
-     * produce a dropdown site switcher
-     * @return ArrayList<Subsite>
-     * @deprecated 3.4.0 Will be removed without equivalent functionality to replace it.
-     */
-    public function ListSubsites()
-    {
-        Deprecation::notice('3.4.0', 'Use SubsiteSwitchList() instead.');
-        return static::SubsiteSwitchList();
-    }
-
     public function alternateMenuDisplayCheck($controllerName)
     {
         if (!class_exists($controllerName ?? '')) {
diff --git a/templates/SilverStripe/Admin/LeftAndMain_Menu.ss b/templates/SilverStripe/Admin/LeftAndMain_Menu.ss
index 095ce918..0f7d6918 100644
--- a/templates/SilverStripe/Admin/LeftAndMain_Menu.ss
+++ b/templates/SilverStripe/Admin/LeftAndMain_Menu.ss
@@ -6,6 +6,7 @@
         <% include SilverStripe\\Admin\\LeftAndMain_MenuStatus %>
 
         <% if $SubsiteSwitchList.Count > 1 %>
+            <% require javascript('silverstripe/subsites:client/dist/js/LeftAndMain_Subsites.js') %>
             <% include SilverStripe\\Subsites\\Controller\\SubsiteXHRController_subsitelist %>
         <% end_if %>
     </div>