diff --git a/app/assets/javascripts/discourse/app/lib/plugin-api.gjs b/app/assets/javascripts/discourse/app/lib/plugin-api.gjs
index 371908c9868..f7e04481e09 100644
--- a/app/assets/javascripts/discourse/app/lib/plugin-api.gjs
+++ b/app/assets/javascripts/discourse/app/lib/plugin-api.gjs
@@ -3211,7 +3211,7 @@ class PluginApi {
         {
           since: "v3.3.0.beta1-dev",
           id: "discourse.header-widget-overrides",
-          url: "https://meta.discourse.org/t/296544",
+          url: "https://meta.discourse.org/t/316549",
         }
       );
     }
diff --git a/app/assets/javascripts/discourse/app/services/header.js b/app/assets/javascripts/discourse/app/services/header.js
index e894b5c8af5..dafe0cf9e88 100644
--- a/app/assets/javascripts/discourse/app/services/header.js
+++ b/app/assets/javascripts/discourse/app/services/header.js
@@ -76,13 +76,20 @@ export default class Header extends Service {
     if (this.siteSettings.glimmer_header_mode === "disabled") {
       return false;
     } else if (this.siteSettings.glimmer_header_mode === "enabled") {
+      if (this.anyWidgetHeaderOverrides) {
+        // eslint-disable-next-line no-console
+        console.error(
+          "Using modern 'glimmer' header, even though there are themes and/or plugins using deprecated APIs. Deprecated header customizations will be broken. (glimmer_header_mode: enabled) https://meta.discourse.org/t/316549"
+        );
+      }
+
       return true;
     } else {
       // Auto
       if (this.anyWidgetHeaderOverrides) {
         // eslint-disable-next-line no-console
         console.warn(
-          "Using legacy 'widget' header because themes and/or plugins are using deprecated APIs. https://meta.discourse.org/t/296544"
+          "Using legacy 'widget' header because themes and/or plugins are using deprecated APIs. (glimmer_header_mode: auto) https://meta.discourse.org/t/316549"
         );
         return false;
       } else {
diff --git a/config/locales/server.en.yml b/config/locales/server.en.yml
index aff2d7474ed..883ef0379c4 100644
--- a/config/locales/server.en.yml
+++ b/config/locales/server.en.yml
@@ -2674,7 +2674,7 @@ en:
     experimental_topics_filter: "EXPERIMENTAL: Enables the experimental topics filter route at /filter"
     enable_experimental_lightbox: "EXPERIMENTAL: Replace the default image lightbox with the revamped design."
     enable_experimental_bookmark_redesign_groups: "EXPERIMENTAL: Show a quick access menu for bookmarks on posts and a new redesigned modal"
-    glimmer_header_mode: "Control whether the new 'glimmer' header implementation is used. Defaults to 'auto', which will enable automatically once all your themes and plugins are ready. https://meta.discourse.org/t/296544"
+    glimmer_header_mode: "Control whether the new 'glimmer' header implementation is used. 'auto' will enable automatically once all your themes and plugins are ready. https://meta.discourse.org/t/316549"
     experimental_glimmer_topic_list_groups: "EXPERIMENTAL: Enable the new 'glimmer' topic list implementation. This implementation is under active development, and is not intended for production use. Do not develop themes/plugins against it until the implementation is finalized and announced."
     experimental_form_templates: "EXPERIMENTAL: Enable the form templates feature. <b>After enabled,</b> manage the templates at <a href='%{base_path}/admin/customize/form-templates'>Customize / Templates</a>."
     admin_sidebar_enabled_groups: "Enable sidebar navigation for the admin UI for the specified groups, which replaces the top-level admin navigation buttons."
diff --git a/config/site_settings.yml b/config/site_settings.yml
index 216ed3c0796..aa4807127b6 100644
--- a/config/site_settings.yml
+++ b/config/site_settings.yml
@@ -2410,7 +2410,7 @@ developer:
       - disabled
       - auto
       - enabled
-    default: auto
+    default: enabled
   admin_sidebar_enabled_groups:
     type: group_list
     list_type: compact