diff --git a/packages/google-chat/protos/google/apps/card/v1/card.proto b/packages/google-chat/protos/google/apps/card/v1/card.proto
index f70c68c2910..c6f659256c9 100644
--- a/packages/google-chat/protos/google/apps/card/v1/card.proto
+++ b/packages/google-chat/protos/google/apps/card/v1/card.proto
@@ -1,4 +1,4 @@
-// Copyright 2025 Google LLC
+// Copyright 2026 Google LLC
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -1197,6 +1197,26 @@ message SelectionInput {
     SWITCH = 2;
 
     // A dropdown menu. Users can select one item from the menu.
+    //
+    // For Google Chat apps, you can populate items using a dynamic data source
+    // and autosuggest items as users type in the menu. For example, users can
+    // start typing the name of a Google Chat space and the widget autosuggests
+    // the space. To dynamically populate items for a dropdown menu, use one of
+    // the following types of data sources:
+    //
+    //  * Google Workspace data: Items are populated using data from Google
+    //    Workspace, such as Google Workspace users or Google Chat spaces.
+    //  * External data: Items are populated from an external data
+    //    source outside of Google Workspace.
+    //
+    // For examples of how to implement dropdown menus for Chat apps, see
+    // [Add a dropdown
+    // menu](https://developers.google.com/workspace/chat/design-interactive-card-dialog#dropdown-menu)
+    // and [Dynamically populate drop-down
+    // menus](https://developers.google.com/workspace/chat/design-interactive-card-dialog#dynamic-dropdown-menu).
+    //
+    // [Google Workspace add-ons and Chat
+    // apps](https://developers.google.com/workspace/extend):
     DROPDOWN = 3;
 
     // A menu with a text box. Users can type and select one or more items.