From 81dc6c1175fabc0acb7cbdd50c8f3db88bfef9b8 Mon Sep 17 00:00:00 2001
From: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Date: Thu, 29 Oct 2026 17:04:26 -0700
Subject: [PATCH] fix(proxy): encode non-dict Mapping Responses chunks as JSON
 objects

---
 litellm/proxy/proxy_server.py                       |  2 +-
 .../proxy/proxy_server/test_streaming_helpers.py    | 13 ++++++++++---
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/litellm/proxy/proxy_server.py b/litellm/proxy/proxy_server.py
index a6648e47de6..aef2bca785c 100644
--- a/litellm/proxy/proxy_server.py
+++ b/litellm/proxy/proxy_server.py
@@ -10204,7 +10204,7 @@ def _format_streaming_sse_chunk(chunk: object) -> str | bytes:
 
 def _format_responses_sse_chunk(chunk: object) -> str | bytes:
     if isinstance(chunk, Mapping):
-        return f"data: {json.dumps(chunk, default=str)}\n\n"
+        return f"data: {json.dumps({**chunk}, default=str)}\n\n"
     return _format_streaming_sse_chunk(chunk=chunk)
 
 
diff --git a/tests/unit/proxy/proxy_server/test_streaming_helpers.py b/tests/unit/proxy/proxy_server/test_streaming_helpers.py
index b3a6e7b1fbf..b75a2494588 100644
--- a/tests/unit/proxy/proxy_server/test_streaming_helpers.py
+++ b/tests/unit/proxy/proxy_server/test_streaming_helpers.py
@@ -18,6 +18,7 @@ from __future__ import annotations
 import asyncio
 import json
 from collections.abc import AsyncIterator, Callable, Mapping
+from types import MappingProxyType
 from typing import Final, Literal
 from unittest.mock import AsyncMock, MagicMock
 
@@ -148,8 +149,14 @@ async def test_responses_stream_dispatches_named_events_without_a_chat_done_sent
 
 
 @pytest.mark.asyncio
-@pytest.mark.parametrize("as_mapping", [False, True])
-async def test_responses_stream_sends_no_failure_event_after_an_upstream_error_event(as_mapping: bool) -> None:
+@pytest.mark.parametrize(
+    "as_chunk",
+    [lambda event: event, lambda event: event.model_dump(), lambda event: MappingProxyType(event.model_dump())],
+    ids=["model", "dict", "mapping_proxy"],
+)
+async def test_responses_stream_sends_no_failure_event_after_an_upstream_error_event(
+    as_chunk: Callable[[ErrorEvent], BaseModel | Mapping[str, object]],
+) -> None:
     response: Final = ResponsesAPIResponse(id="resp_error_then_raise", created_at=1, model="local-model", output=[])
     created: Final = ResponseCreatedEvent.model_validate(
         {"type": "response.created", "sequence_number": 0, "response": response}
@@ -160,7 +167,7 @@ async def test_responses_stream_sends_no_failure_event_after_an_upstream_error_e
 
     async def upstream() -> AsyncIterator[BaseModel | Mapping[str, object]]:
         yield created
-        yield error_event.model_dump() if as_mapping else error_event
+        yield as_chunk(error_event)
         raise litellm.APIError(status_code=500, message="Stream close failed", llm_provider="openai", model="local-model")
 
     frames: Final = tuple(