diff --git a/run_agent.py b/run_agent.py
index ae5c3b5deb..5170178b70 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -1323,16 +1323,6 @@ class AIAgent:
                                     call_id = f"call_{uuid.uuid4().hex[:12]}"
                             call_id = call_id.strip()
 
-                            response_item_id = tc.get("response_item_id")
-                            if not isinstance(response_item_id, str) or not response_item_id.strip():
-                                response_item_id = tc.get("responses_item_id")
-                            if not isinstance(response_item_id, str) or not response_item_id.strip():
-                                response_item_id = embedded_response_item_id
-                            response_item_id = self._derive_responses_function_call_id(
-                                call_id,
-                                response_item_id if isinstance(response_item_id, str) else None,
-                            )
-
                             arguments = fn.get("arguments", "{}")
                             if isinstance(arguments, dict):
                                 arguments = json.dumps(arguments, ensure_ascii=False)
@@ -1342,7 +1332,6 @@ class AIAgent:
 
                             items.append({
                                 "type": "function_call",
-                                "id": response_item_id,
                                 "call_id": call_id,
                                 "name": fn_name,
                                 "arguments": arguments,
diff --git a/tests/test_run_agent_codex_responses.py b/tests/test_run_agent_codex_responses.py
index d4fd75ebf7..7121cc5720 100644
--- a/tests/test_run_agent_codex_responses.py
+++ b/tests/test_run_agent_codex_responses.py
@@ -300,7 +300,7 @@ def test_run_conversation_codex_tool_round_trip(monkeypatch):
     assert any(msg.get("role") == "tool" and msg.get("tool_call_id") == "call_1" for msg in result["messages"])
 
 
-def test_chat_messages_to_responses_input_uses_fc_id_for_function_call(monkeypatch):
+def test_chat_messages_to_responses_input_uses_call_id_for_function_call(monkeypatch):
     agent = _build_agent(monkeypatch)
     items = agent._chat_messages_to_responses_input(
         [
@@ -324,7 +324,7 @@ def test_chat_messages_to_responses_input_uses_fc_id_for_function_call(monkeypat
     function_output = next(item for item in items if item.get("type") == "function_call_output")
 
     assert function_call["call_id"] == "call_abc123"
-    assert function_call["id"] == "fc_abc123"
+    assert "id" not in function_call
     assert function_output["call_id"] == "call_abc123"
 
 
@@ -352,11 +352,11 @@ def test_chat_messages_to_responses_input_accepts_call_pipe_fc_ids(monkeypatch):
     function_output = next(item for item in items if item.get("type") == "function_call_output")
 
     assert function_call["call_id"] == "call_pair123"
-    assert function_call["id"] == "fc_pair123"
+    assert "id" not in function_call
     assert function_output["call_id"] == "call_pair123"
 
 
-def test_run_conversation_codex_replay_payload_keeps_call_id_and_fc_id(monkeypatch):
+def test_run_conversation_codex_replay_payload_keeps_call_id(monkeypatch):
     agent = _build_agent(monkeypatch)
     responses = [_codex_tool_call_response(), _codex_message_response("done")]
     requests = []
@@ -389,7 +389,7 @@ def test_run_conversation_codex_replay_payload_keeps_call_id_and_fc_id(monkeypat
     function_call = next(item for item in replay_input if item.get("type") == "function_call")
     function_output = next(item for item in replay_input if item.get("type") == "function_call_output")
     assert function_call["call_id"] == "call_1"
-    assert function_call["id"] == "fc_1"
+    assert "id" not in function_call
     assert function_output["call_id"] == "call_1"