perf: optimize RunState memory with slots and faster list operations

Author: KirobotDev

src/agents/run.py

@@ -559,7 +559,7 @@ async def run(
                 raw_original_input = run_state._original_input
                 original_input = normalize_resumed_input(raw_original_input)
                 generated_items = run_state._generated_items
-                session_items = list(run_state._session_items)
+                session_items = run_state._session_items[:]
                 model_responses = run_state._model_responses
                 # Cast to the correct type since we know this is TContext
                 context_wrapper = cast(RunContextWrapper[TContext], run_state._context)
@@ -591,7 +591,7 @@ def _with_reasoning_item_id_policy(result: RunResult) -> RunResult:
 
             pending_server_items: list[RunItem] | None = None
             input_guardrail_results: list[InputGuardrailResult] = (
-                list(run_state._input_guardrail_results) if run_state is not None else []
+                run_state._input_guardrail_results[:] if run_state is not None else []
             )
             tool_input_guardrail_results: list[ToolInputGuardrailResult] = (
                 list(getattr(run_state, "_tool_input_guardrail_results", []))
@@ -624,7 +624,7 @@ def _with_reasoning_item_id_policy(result: RunResult) -> RunResult:
 
             if session_persistence_enabled and session_input_items_for_persistence:
                 # Capture the exact input saved so it can be rewound on conversation lock retries.
-                last_saved_input_snapshot_for_rewind = list(session_input_items_for_persistence)
+                last_saved_input_snapshot_for_rewind = session_input_items_for_persistence[:]
                 await save_result_to_session(
                     session,
                     session_input_items_for_persistence,
@@ -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:
@@ -1101,13 +1099,13 @@ def _with_reasoning_item_id_policy(result: RunResult) -> RunResult:
                     turn_session_items = session_items_for_turn(turn_result)
                     session_items.extend(turn_session_items)
                     if server_conversation_tracker is not None:
-                        pending_server_items = list(turn_result.new_step_items)
+                        pending_server_items = turn_result.new_step_items[:]
                         server_conversation_tracker.track_server_items(turn_result.model_response)
 
                     tool_input_guardrail_results.extend(turn_result.tool_input_guardrail_results)
                     tool_output_guardrail_results.extend(turn_result.tool_output_guardrail_results)
 
-                    items_to_save_turn = list(turn_session_items)
+                    items_to_save_turn = turn_session_items[:]
                     if not isinstance(turn_result.next_step, NextStepInterruption):
                         # When resuming a turn we have already persisted the tool_call items;
                         if (
@@ -1207,9 +1205,9 @@ 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 = (

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.