From 765b129ab49badf60f08cab8a19ffcbb0f389ed7 Mon Sep 17 00:00:00 2001
From: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Date: Thu, 29 Oct 2026 12:23:59 -0700
Subject: [PATCH] fix(responses): keep a dict tool call's thought signature on
 the streamed function_call done item

---
 .../streaming_iterator.py                     |  7 +++++-
 .../test_litellm_completion_responses.py      | 23 +++++++++++++++++++
 2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/litellm/responses/litellm_completion_transformation/streaming_iterator.py b/litellm/responses/litellm_completion_transformation/streaming_iterator.py
index 0721968441c..394f221e0d0 100644
--- a/litellm/responses/litellm_completion_transformation/streaming_iterator.py
+++ b/litellm/responses/litellm_completion_transformation/streaming_iterator.py
@@ -93,7 +93,12 @@ def _tool_call_objects(tool_calls: object) -> tuple[object, ...]:
 
 
 def _tool_call_provider_specific_fields(tool_call: object) -> Mapping[str, object]:
-    fields: Final[object] = getattr(tool_call, "provider_specific_fields", None)
+    mapping: Final = as_str_mapping(tool_call)
+    fields: Final[object] = (
+        mapping.get("provider_specific_fields")
+        if mapping is not None
+        else getattr(tool_call, "provider_specific_fields", None)
+    )
     return {"provider_specific_fields": fields} if fields else {}
 
 
diff --git a/tests/unit/responses/litellm_completion_transformation/test_litellm_completion_responses.py b/tests/unit/responses/litellm_completion_transformation/test_litellm_completion_responses.py
index 7a5254b64f4..a6a1335fdc4 100644
--- a/tests/unit/responses/litellm_completion_transformation/test_litellm_completion_responses.py
+++ b/tests/unit/responses/litellm_completion_transformation/test_litellm_completion_responses.py
@@ -4746,6 +4746,29 @@ class TestEnsureOutputItemContentPartAdded:
         assert done.item.name == "spawn_agent"
         assert done.item.namespace == "collaboration"
 
+    def test_streaming_final_only_dict_tool_call_keeps_its_provider_specific_fields(self):
+        from unittest.mock import MagicMock
+
+        iterator = self._make_iterator()
+        iterator.tool_call_provider_fields = True
+        provider_specific_fields = {"thought_signature": "sig-" + "x" * 512}
+        message = MagicMock()
+        message.tool_calls = [
+            {
+                "id": "call_1",
+                "function": {"name": "get_weather", "arguments": '{"city":"Paris"}'},
+                "provider_specific_fields": provider_specific_fields,
+            }
+        ]
+        complete_response = MagicMock()
+        complete_response.choices = [MagicMock(message=message)]
+
+        iterator._queue_final_tool_call_done_events(complete_response)
+
+        done = iterator._pending_tool_events[-1]
+        assert done.type == "response.output_item.done"
+        assert done.item.provider_specific_fields == provider_specific_fields
+
     def test_streaming_top_level_function_collision_stays_unnamespaced(self):
         iterator = self._make_iterator()
         iterator.responses_api_request = {