From aa6fd8971d79e71f750ac63b671bb6f99c46b4ef Mon Sep 17 00:00:00 2001
From: Vedant-2-6 <vedantpatelvp04@gmail.com>
Date: Mon, 31 Aug 2026 18:43:24 +0530
Subject: [PATCH] fix: add reasoning_items to unsupported_delta_fields in
 streaming serializer

The fast-serialization path dropped delta.reasoning_items by classifying
chunks with empty content and reasoning_items as simple text. Adding the field
to unsupported_delta_fields causes such chunks to fall through to model_dump_json,
preserving the encrypted reasoning state for multi-turn tool loops.

Fixes #38907
---
 litellm/proxy/proxy_server.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/litellm/proxy/proxy_server.py b/litellm/proxy/proxy_server.py
index 887716a383a..657e11ad31b 100644
--- a/litellm/proxy/proxy_server.py
+++ b/litellm/proxy/proxy_server.py
@@ -8268,6 +8268,7 @@ def _fast_serialize_simple_model_response_stream(
         "thinking_blocks",
         "provider_specific_fields",
         "refusal",
+        "reasoning_items",
     )
     if any(getattr(delta, field, None) is not None for field in unsupported_delta_fields):
         return None