diff --git a/backend/open_webui/main.py b/backend/open_webui/main.py
index 12efc21ab1..40ec12dd9e 100644
--- a/backend/open_webui/main.py
+++ b/backend/open_webui/main.py
@@ -1259,7 +1259,7 @@ async def chat_completion(
                         target_model_id = entry['model_id']
                         assistant_message_id = entry['message_id']
                         if assistant_message_id:
-                            history_messages[assistant_message_id] = {
+                            assistant_message = {
                                 'id': assistant_message_id,
                                 'parentId': user_message_id,
                                 'childrenIds': [],
@@ -1269,6 +1269,11 @@ async def chat_completion(
                                 'model': target_model_id,
                                 'timestamp': int(time.time()),
                             }
+                            # Preserve the side-by-side column index so duplicate
+                            # models don't collapse into one another on reload.
+                            if entry.get('modelIdx') is not None:
+                                assistant_message['modelIdx'] = entry['modelIdx']
+                            history_messages[assistant_message_id] = assistant_message
 
                     await Chats.insert_new_chat(
                         chat_id,
@@ -1481,19 +1486,24 @@ async def chat_completion(
                         target_model_id = entry['model_id']
                         assistant_message_id = entry['message_id']
                         if assistant_message_id:
+                            assistant_message = {
+                                'id': assistant_message_id,
+                                'parentId': user_message_id,
+                                'childrenIds': [],
+                                'role': 'assistant',
+                                'content': '',
+                                'done': False,
+                                'model': target_model_id,
+                                'timestamp': int(time.time()),
+                            }
+                            # Preserve the side-by-side column index so duplicate
+                            # models don't collapse into one another on reload.
+                            if entry.get('modelIdx') is not None:
+                                assistant_message['modelIdx'] = entry['modelIdx']
                             await Chats.upsert_message_to_chat_by_id_and_message_id(
                                 chat_id,
                                 assistant_message_id,
-                                {
-                                    'id': assistant_message_id,
-                                    'parentId': user_message_id,
-                                    'childrenIds': [],
-                                    'role': 'assistant',
-                                    'content': '',
-                                    'done': False,
-                                    'model': target_model_id,
-                                    'timestamp': int(time.time()),
-                                },
+                                assistant_message,
                             )
                             await publish_event(
                                 request,
diff --git a/src/lib/components/chat/Chat.svelte b/src/lib/components/chat/Chat.svelte
index f1bc26ffd9..5d657e92f8 100644
--- a/src/lib/components/chat/Chat.svelte
+++ b/src/lib/components/chat/Chat.svelte
@@ -2777,9 +2777,11 @@
 				: selectedModels;
 
 		// Create response messages for each selected model
-		// Build message_ids list: [{model_id, message_id}, ...]
+		// Build message_ids list: [{model_id, message_id, modelIdx}, ...]
 		// Uses an array instead of a dict to support duplicate model IDs in side-by-side chat.
-		const messageIdsList: Array<{ model_id: string; message_id: string }> = [];
+		// modelIdx identifies each side-by-side column so the backend can persist it; without
+		// it, duplicate models collapse into one another when the chat is reloaded.
+		const messageIdsList: Array<{ model_id: string; message_id: string; modelIdx: number }> = [];
 		for (const [_modelIdx, modelId] of selectedModelIds.entries()) {
 			const model = $models.filter((m) => m.id === modelId).at(0);
 
@@ -2811,7 +2813,11 @@
 				}
 
 				responseMessageIds[`${modelId}-${modelIdx ? modelIdx : _modelIdx}`] = responseMessageId;
-				messageIdsList.push({ model_id: modelId, message_id: responseMessageId });
+				messageIdsList.push({
+					model_id: modelId,
+					message_id: responseMessageId,
+					modelIdx: modelIdx ? modelIdx : _modelIdx
+				});
 			}
 		}
 		history = history;
@@ -2890,7 +2896,11 @@
 					primaryResponseMessageId,
 					_chatId,
 					{
-						messageIdsList: selectedModelIds.length > 1 ? messageIdsList : undefined,
+						// Always forward the message_ids list (not just for multi-model sends) so the
+						// backend persists each response's modelIdx — including single-column
+						// regenerations in a duplicate-model chat, which would otherwise lose their
+						// column identity and collapse on reload.
+						messageIdsList: messageIdsList.length > 0 ? messageIdsList : undefined,
 						regenerationPrompt
 					}
 				);