diff --git a/eval_protocol/mcp/execution/base_policy.py b/eval_protocol/mcp/execution/base_policy.py
index bdced48a..9d44d02c 100644
--- a/eval_protocol/mcp/execution/base_policy.py
+++ b/eval_protocol/mcp/execution/base_policy.py
@@ -199,6 +199,13 @@ async def _generate_live_tool_calls(
         if message.get("tool_calls"):
             assistant_message_for_history["tool_calls"] = message["tool_calls"]
 
+        # Preserve specific fields from provider_specific_fields if present
+        if message.get("provider_specific_fields"):
+            if message["provider_specific_fields"].get("reasoning_details"):
+                assistant_message_for_history["reasoning_details"] = message["provider_specific_fields"][
+                    "reasoning_details"
+                ]
+
         # Add to actual conversation history
         conversation_history.append(assistant_message_for_history)
 
diff --git a/eval_protocol/mcp/execution/policy.py b/eval_protocol/mcp/execution/policy.py
index 777c4f7e..0b4aac4e 100644
--- a/eval_protocol/mcp/execution/policy.py
+++ b/eval_protocol/mcp/execution/policy.py
@@ -146,7 +146,7 @@ def _clean_messages_for_api(self, messages: List[Dict]) -> List[Dict]:
             Clean messages with only OpenAI API compatible fields
         """
         # Standard OpenAI message fields
-        allowed_fields = {"role", "content", "tool_calls", "tool_call_id", "name"}
+        allowed_fields = {"role", "content", "tool_calls", "tool_call_id", "name", "reasoning_details"}
 
         clean_messages = []
         for msg in messages:
@@ -217,12 +217,15 @@ async def _make_llm_call(self, messages: List[Dict[str, Any]], tools: List[Dict[
                 logger.debug(f"🔄 API call for model: {self.model_id}")
 
             # LiteLLM already returns OpenAI-compatible format
+            message_obj = getattr(response.choices[0], "message", object())
+
             return {
                 "choices": [
                     {
                         "message": {
-                            "role": getattr(getattr(response.choices[0], "message", object()), "role", "assistant"),
-                            "content": getattr(getattr(response.choices[0], "message", object()), "content", None),
+                            "role": getattr(message_obj, "role", "assistant"),
+                            "content": getattr(message_obj, "content", None),
+                            "provider_specific_fields": getattr(message_obj, "provider_specific_fields", None),
                             "tool_calls": (
                                 [
                                     {
@@ -233,12 +236,9 @@ async def _make_llm_call(self, messages: List[Dict[str, Any]], tools: List[Dict[
                                             "arguments": getattr(getattr(tc, "function", None), "arguments", "{}"),
                                         },
                                     }
-                                    for tc in (
-                                        getattr(getattr(response.choices[0], "message", object()), "tool_calls", [])
-                                        or []
-                                    )
+                                    for tc in (getattr(message_obj, "tool_calls", []) or [])
                                 ]
-                                if getattr(getattr(response.choices[0], "message", object()), "tool_calls", None)
+                                if getattr(message_obj, "tool_calls", None)
                                 else []
                             ),
                         },
diff --git a/tests/test_litellm_policy_provider_fields.py b/tests/test_litellm_policy_provider_fields.py
new file mode 100644
index 00000000..6812ef9b
--- /dev/null
+++ b/tests/test_litellm_policy_provider_fields.py
@@ -0,0 +1,95 @@
+import types
+
+import pytest
+
+import eval_protocol.mcp.execution.policy as policy_mod
+from eval_protocol.mcp.execution.policy import LiteLLMPolicy
+
+
+@pytest.mark.asyncio
+async def test_litellm_policy_surfaces_provider_specific_reasoning_details(monkeypatch):
+    """
+    Ensure that provider_specific_fields from the LiteLLM message object are
+    preserved on the returned message dict from LiteLLMPolicy._make_llm_call.
+    """
+
+    # Define a fake ModelResponse base class and patch the module's ModelResponse
+    class FakeModelResponseBase: ...
+
+    policy_mod.ModelResponse = FakeModelResponseBase
+
+    async def fake_acompletion(*args, **kwargs):
+        # This mimics the LiteLLM Message object shape we rely on in policy._make_llm_call
+        message_obj = types.SimpleNamespace(
+            role="assistant",
+            content="",
+            tool_calls=[
+                types.SimpleNamespace(
+                    id="tool_get_reservation_details_123",
+                    type="function",
+                    function=types.SimpleNamespace(
+                        name="get_reservation_details",
+                        arguments='{"reservation_id":"EHGLP3"}',
+                    ),
+                )
+            ],
+            provider_specific_fields={
+                "reasoning_details": [{"id": "tool_get_reservation_details_123", "type": "reasoning.encrypted"}],
+                "custom_field": "keep_me",
+            },
+        )
+
+        class FakeModelResponse(FakeModelResponseBase):
+            def __init__(self) -> None:
+                self.choices = [
+                    types.SimpleNamespace(
+                        finish_reason="tool_calls",
+                        index=0,
+                        message=message_obj,
+                    )
+                ]
+                self.usage = types.SimpleNamespace(
+                    prompt_tokens=10,
+                    completion_tokens=5,
+                    total_tokens=15,
+                )
+
+        return FakeModelResponse()
+
+    # Patch acompletion so we don't hit the network
+    monkeypatch.setattr(policy_mod, "acompletion", fake_acompletion)
+
+    # Use a concrete policy instance; base_url/model_id values don't matter for this unit test
+    policy = LiteLLMPolicy(model_id="openrouter/google/gemini-3-pro-preview", use_caching=False)
+
+    messages = [
+        {
+            "role": "assistant",
+            "content": "",
+            "tool_calls": [
+                {
+                    "id": "tool_get_reservation_details_123",
+                    "type": "function",
+                    "function": {"name": "get_reservation_details", "arguments": '{"reservation_id":"EHGLP3"}'},
+                }
+            ],
+        }
+    ]
+
+    # No tools are needed for this test – we only care about the returned message shape
+    result = await policy._make_llm_call(messages, tools=[])
+
+    assert "choices" in result
+    assert len(result["choices"]) == 1
+    msg = result["choices"][0]["message"]
+
+    # Core fields should be present
+    assert msg["role"] == "assistant"
+    assert isinstance(msg.get("tool_calls"), list)
+
+    # provider_specific_fields should be preserved on the message
+    ps = msg.get("provider_specific_fields")
+    assert isinstance(ps, dict)
+    assert ps["reasoning_details"] == [{"id": "tool_get_reservation_details_123", "type": "reasoning.encrypted"}]
+    # Non-core provider_specific_fields should also be preserved
+    assert ps.get("custom_field") == "keep_me"