diff --git a/src/agents/run.py b/src/agents/run.py
index 047d454d35..4f558ed99b 100644
--- a/src/agents/run.py
+++ b/src/agents/run.py
@@ -797,12 +797,12 @@ def _with_reasoning_item_id_policy(result: RunResult) -> RunResult:
                                     max_turns=max_turns,
                                 )
                                 result._current_turn = current_turn
-                                result._model_input_items = list(generated_items)
+                                result._model_input_items = generated_items[:]
                                 # Keep normalized replay aligned with the model-facing
                                 # continuation whenever session history preserved extra items.
-                                result._replay_from_model_input_items = list(
-                                    generated_items
-                                ) != list(session_items)
+                                result._replay_from_model_input_items = (
+                                    generated_items != session_items
+                                )
                                 if run_state is not None:
                                     result._trace_state = run_state._trace_state
                                 if session_persistence_enabled:
@@ -936,10 +936,8 @@ def _with_reasoning_item_id_policy(result: RunResult) -> RunResult:
                             max_turns=max_turns,
                         )
                         result._current_turn = max_turns
-                        result._model_input_items = list(generated_items)
-                        result._replay_from_model_input_items = list(generated_items) != list(
-                            session_items
-                        )
+                        result._model_input_items = generated_items[:]
+                        result._replay_from_model_input_items = generated_items != session_items
                         if run_state is not None:
                             result._trace_state = run_state._trace_state
                         if session_persistence_enabled and include_in_history:
@@ -1207,10 +1205,8 @@ def _with_reasoning_item_id_policy(result: RunResult) -> RunResult:
                                 max_turns=max_turns,
                             )
                             result._current_turn = current_turn
-                            result._model_input_items = list(generated_items)
-                            result._replay_from_model_input_items = list(generated_items) != list(
-                                session_items
-                            )
+                            result._model_input_items = generated_items[:]
+                            result._replay_from_model_input_items = generated_items != session_items
                             if run_state is not None:
                                 result._current_turn_persisted_item_count = (
                                     run_state._current_turn_persisted_item_count
diff --git a/src/agents/run_state.py b/src/agents/run_state.py
index dcda9e073c..e03b6c67ab 100644
--- a/src/agents/run_state.py
+++ b/src/agents/run_state.py
@@ -135,7 +135,7 @@
 _MISSING_CONTEXT_SENTINEL = object()
 
 
-@dataclass
+@dataclass(slots=True)
 class RunState(Generic[TContext, TAgent]):
     """Serializable snapshot of an agent run, including context, usage, and interruptions.