diff --git a/src/agents/models/chatcmpl_converter.py b/src/agents/models/chatcmpl_converter.py
index 25d9f083..31dc6f8f 100644
--- a/src/agents/models/chatcmpl_converter.py
+++ b/src/agents/models/chatcmpl_converter.py
@@ -302,7 +302,11 @@ def ensure_assistant_message() -> ChatCompletionAssistantMessageParam:
             return current_assistant_msg
 
         for item in items:
-            # 1) Check easy input message
+                        # 1) Ignore reasoning items, which are not sent to the LLM.
+            if isinstance(item, dict) and item.get("type") == "reasoning":
+                continue
+
+            # 2) Check easy input message
             if easy_msg := cls.maybe_easy_input_message(item):
                 role = easy_msg["role"]
                 content = easy_msg["content"]
diff --git a/tests/test_openai_chatcompletions_converter.py b/tests/test_openai_chatcompletions_converter.py
index bcfca549..2591a01e 100644
--- a/tests/test_openai_chatcompletions_converter.py
+++ b/tests/test_openai_chatcompletions_converter.py
@@ -428,3 +428,17 @@ def test_assistant_messages_in_history():
     assert messages[1]["content"] == "Hello?"
     assert messages[2]["role"] == "user"
     assert messages[2]["content"] == "What was my Name?"
+
+
+def test_items_to_messages_ignores_reasoning_item() -> None:
+    """
+    A `reasoning` item in the input should be ignored, resulting in an empty
+    message list if it's the only item.
+    """
+    reasoning_item: TResponseInputItem = {
+        "type": "reasoning",
+        "reasoning": "Thinking about what to do...",  # type: ignore
+    }
+    messages = Converter.items_to_messages([reasoning_item])
+    assert len(messages) == 0
+