From d75a7aaf5453e79b6224d49819c27ea5a6f86d15 Mon Sep 17 00:00:00 2001
From: Classic298 <27028174+Classic298@users.noreply.github.com>
Date: Fri, 4 Sep 2026 23:17:02 +0200
Subject: [PATCH] fix: surface upstream errors on arena models instead of
 crashing (#29662)

Sending a message to an arena model failed with "'JSONResponse' object has no attribute 'body_iterator'" whenever the backing provider answered with an HTTP error, so the real error never reached the user. Non-streaming requests on an arena model, such as title and tag generation, broke the same way with "'JSONResponse' object is not a mapping".

The arena wrapper assumed the sub-model call always returns a stream for a streaming request and a dict for everything else, but the OpenAI-compatible router returns a plain response object as soon as the provider answers 4xx or 5xx. Both arms now hand that response straight back, which is exactly what the non-arena path already does, so the existing error handling turns it into the usual error message in the chat.

Verified against a matrix of streaming and non-streaming requests with the sub-model returning a stream, a dict, a JSONResponse and a PlainTextResponse: both crashes are gone and the two success paths are unchanged, including the selected_model_id prelude on the stream.

Fixes #29658
---
 backend/open_webui/utils/chat.py | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/backend/open_webui/utils/chat.py b/backend/open_webui/utils/chat.py
index a769d5f1df..0b64a52165 100644
--- a/backend/open_webui/utils/chat.py
+++ b/backend/open_webui/utils/chat.py
@@ -269,24 +269,25 @@ async def generate_chat_completion(
                     bypass_filter=True,
                     bypass_system_prompt=bypass_system_prompt,
                 )
+                # Upstream errors come back as a response object.
+                if not isinstance(response, StreamingResponse):
+                    return response
                 return StreamingResponse(
                     stream_wrapper(response.body_iterator),
                     media_type='text/event-stream',
                     background=response.background,
                 )
             else:
-                return {
-                    **(
-                        await generate_chat_completion(
-                            request,
-                            form_data,
-                            user,
-                            bypass_filter=True,
-                            bypass_system_prompt=bypass_system_prompt,
-                        )
-                    ),
-                    'selected_model_id': selected_model_id,
-                }
+                response = await generate_chat_completion(
+                    request,
+                    form_data,
+                    user,
+                    bypass_filter=True,
+                    bypass_system_prompt=bypass_system_prompt,
+                )
+                if not isinstance(response, dict):
+                    return response
+                return {**response, 'selected_model_id': selected_model_id}
 
         if model.get('pipe'):
             # Below does not require bypass_filter because this is the only route the uses this function and it is already bypassing the filter