diff --git a/app/assets/styles.css b/app/assets/styles.css
index 568ad17c..53758712 100644
--- a/app/assets/styles.css
+++ b/app/assets/styles.css
@@ -27,6 +27,14 @@ html {
   vertical-align: middle;
 }
 
+.deprecated-warning {
+  padding: var(--spacing-2);
+  border-radius: var(--radius-lg);
+  border: 1px solid var(--color-gray-800);
+  margin-bottom: var(--spacing-2);
+  line-break: anywhere;
+}
+
 main a.edit-icon {
   height: 1rem;
   width: 16px;
diff --git a/app/components/class-field-description.gjs b/app/components/class-field-description.gjs
index 436d298f..bc31b607 100644
--- a/app/components/class-field-description.gjs
+++ b/app/components/class-field-description.gjs
@@ -142,6 +142,19 @@ export default class ClassFieldDescription extends Component {
           </div>
         {{/if}}
       </dl>
+
+      {{#if @field.deprecated}}
+        <div class="deprecated-warning">
+          <h4>This {{@type}} is deprecated!</h4>
+          {{#if @field.deprecationMessage}}
+            <MarkdownToHtml
+              @markdown={{@field.deprecationMessage}}
+              @simplifiedAutoLink={{true}}
+            />
+          {{/if}}
+        </div>
+      {{/if}}
+
       <MarkdownToHtml @markdown={{@field.description}} />
     </section>
   </template>
diff --git a/app/models/class.js b/app/models/class.js
index 39208d0a..ddffdccd 100644
--- a/app/models/class.js
+++ b/app/models/class.js
@@ -13,6 +13,9 @@ export default class Class extends Model {
   @attr()
   deprecated;
 
+  @attr()
+  deprecationMessage;
+
   @attr()
   access;
 
diff --git a/app/models/module.js b/app/models/module.js
index 9fdbf22c..d8a14fdd 100644
--- a/app/models/module.js
+++ b/app/models/module.js
@@ -23,6 +23,9 @@ export default class Module extends ClassModel {
   @attr()
   allstaticfunctions;
 
+  @attr()
+  deprecated;
+
   @belongsTo('project-version', { async: false, inverse: null })
   projectVersion;
 }
diff --git a/app/serializers/application.js b/app/serializers/application.js
index 1d128732..ad36ae15 100644
--- a/app/serializers/application.js
+++ b/app/serializers/application.js
@@ -30,4 +30,11 @@ export default class Application extends JSONAPISerializer {
 
     return normalizedDocument;
   }
+
+  keyForAttribute(key) {
+    if (key === 'deprecationMessage') {
+      return key;
+    }
+    return super.keyForAttribute(key);
+  }
 }
diff --git a/app/templates/project-version/classes/class.gjs b/app/templates/project-version/classes/class.gjs
index 41d65f0b..172e525c 100644
--- a/app/templates/project-version/classes/class.gjs
+++ b/app/templates/project-version/classes/class.gjs
@@ -136,6 +136,16 @@ import ApiIndex from 'ember-api-docs/components/api-index';
         </div>
       {{/if}}
     </div>
+    {{#if @model.deprecated}}
+      <hr />
+      <div class="deprecated-warning">
+        <h2>This class is deprecated!</h2>
+        <p class="description"><MarkdownToHtml
+            @markdown={{@model.deprecationMessage}}
+            @simplifiedAutoLink={{true}}
+          /></p>
+      </div>
+    {{/if}}
     {{#if (and (not (eq @controller.static 1)) @controller.hasImportExample)}}
       <ImportExample @item={{@model.name}} @package={{@controller.module}} />
     {{/if}}
diff --git a/app/templates/project-version/modules/module.gjs b/app/templates/project-version/modules/module.gjs
index 4a1870db..ce63a020 100644
--- a/app/templates/project-version/modules/module.gjs
+++ b/app/templates/project-version/modules/module.gjs
@@ -3,7 +3,9 @@ import { LinkTo } from '@ember/routing';
 import { array } from '@ember/helper';
 import MarkdownToHtml from 'ember-cli-showdown/components/markdown-to-html';
 import not from 'ember-truth-helpers/helpers/not';
+import notEq from 'ember-truth-helpers/helpers/not-eq';
 import and from 'ember-truth-helpers/helpers/and';
+import or from 'ember-truth-helpers/helpers/or';
 import gt from 'ember-truth-helpers/helpers/gt';
 import functionHeadingId from 'ember-api-docs/helpers/function-heading-id';
 import betterGet from 'ember-api-docs/helpers/better-get';
@@ -19,6 +21,9 @@ import betterGet from 'ember-api-docs/helpers/better-get';
           {{#if @controller.model.access}}<span
               class="access"
             >{{@controller.model.access}}</span>{{/if}}
+          {{#if @controller.model.deprecated}}<span
+              class="access"
+            >deprecated</span>{{/if}}
         </h1>
       {{/if}}
     </div>
@@ -122,6 +127,27 @@ import betterGet from 'ember-api-docs/helpers/better-get';
       {{/each}}
 
     {{/if}}
+    {{#if (notEq @controller.model.name "ember-data-overview")}}
+      {{#if
+        (not
+          (or
+            @controller.submodules
+            @controller.classesAndNamespaces
+            (and
+              @controller.functionHeadings
+              (gt @controller.functionHeadings.length 0)
+            )
+          )
+        )
+      }}
+        <p data-test-empty-module-warning>
+          No submodules, classes, namespaces, or functions are visible. Some may
+          be hidden because private and deprecated packages are not shown.
+          Toggle "Show Private / Deprecated packages" in the sidebar to reveal
+          them.
+        </p>
+      {{/if}}
+    {{/if}}
     {{outlet}}
 
   </article>
diff --git a/tests/acceptance/module-test.js b/tests/acceptance/module-test.js
index b2471afc..c605eacf 100644
--- a/tests/acceptance/module-test.js
+++ b/tests/acceptance/module-test.js
@@ -46,6 +46,58 @@ module('Acceptance | Module', function (hooks) {
     assert.equal(findAll('.spec-method-list li').length, numberSubModules);
   });
 
+  test('does not show the empty-module warning when the module has submodules', async function (assert) {
+    await visit('ember/1.0/modules/ember');
+
+    assert
+      .dom('[data-test-empty-module-warning]')
+      .doesNotExist('no warning when module has submodules');
+  });
+
+  test('does not show the empty-module warning when the module has public classes or namespaces', async function (assert) {
+    await visit('ember/1.0/modules/ember-handlebars');
+
+    assert
+      .dom('[data-test-empty-module-warning]')
+      .doesNotExist('no warning when module has public classes');
+  });
+
+  test('does not show the empty-module warning when the module has public functions', async function (assert) {
+    // ember/2.16/modules/jquery has only public static functions ($) and no classes, namespaces, or submodules
+    await visit('ember/2.16/modules/jquery');
+
+    assert
+      .dom('[data-test-empty-module-warning]')
+      .doesNotExist('no warning when module has public functions');
+  });
+
+  test('does not show the empty-module warning on the ember-data-overview page', async function (assert) {
+    // ember-data-overview has no content at all, but is excluded from the warning by name
+    await visit('ember-data/4.7/modules/ember-data-overview');
+
+    assert
+      .dom('[data-test-empty-module-warning]')
+      .doesNotExist(
+        'no warning on ember-data-overview regardless of empty content',
+      );
+  });
+
+  test('shows a note when all content is hidden by the private/deprecated filter', async function (assert) {
+    // ember-htmlbars in 1.13 has only a private class (HandlebarsCompatibleHelper)
+    // and no public classes, namespaces, submodules, or functions
+    await visit('ember/1.13/modules/ember-htmlbars');
+
+    assert
+      .dom('[data-test-empty-module-warning]')
+      .exists('warning shown when no public content is visible');
+
+    await click('[data-test-private-deprecated-toggle]');
+
+    assert
+      .dom('[data-test-empty-module-warning]')
+      .doesNotExist('warning hidden after showing private/deprecated content');
+  });
+
   test('display submodule parent', async function (assert) {
     await visit('ember/1.0/modules/ember-application');