fix(realtime): coalesce response.create across parallel tool calls

src/agents/realtime/model_events.py

@@ -28,6 +28,9 @@ class RealtimeModelToolCallEvent:
     id: str | None = None
     previous_item_id: str | None = None
 
+    response_id: str | None = None
+    """The ID of the model response that produced this tool call."""
+
     type: Literal["function_call"] = "function_call"
 
 
@@ -143,6 +146,9 @@ class RealtimeModelTurnStartedEvent:
 class RealtimeModelTurnEndedEvent:
     """Triggered when the model finishes generating a response for a turn."""
 
+    response_id: str | None = None
+    """The ID of the model response that just finished, if available."""
+
     type: Literal["turn_ended"] = "turn_ended"
 
 

src/agents/realtime/openai_realtime.py

@@ -926,7 +926,9 @@ async def _handle_audio_delta(self, parsed: ResponseAudioDeltaEvent) -> None:
             )
         )
 
-    async def _handle_output_item(self, item: ConversationItem) -> None:
+    async def _handle_output_item(
+        self, item: ConversationItem, response_id: str | None = None
+    ) -> None:
         """Handle response output item events (function calls and messages)."""
         if item.type == "function_call" and item.status == "completed":
             tool_call = RealtimeToolCallItem(
@@ -948,6 +950,7 @@ async def _handle_output_item(self, item: ConversationItem) -> None:
                     name=item.name or "",
                     arguments=item.arguments or "",
                     id=item.id or "",
+                    response_id=response_id,
                 )
             )
         elif item.type == "message":
@@ -1149,7 +1152,9 @@ async def _handle_ws_event(self, event: dict[str, Any]):
             await self._emit_event(RealtimeModelTurnStartedEvent())
         elif parsed.type == "response.done":
             await self._mark_response_done()
-            await self._emit_event(RealtimeModelTurnEndedEvent())
+            await self._emit_event(
+                RealtimeModelTurnEndedEvent(response_id=getattr(parsed.response, "id", None))
+            )
         elif parsed.type == "session.created":
             await self._send_tracing_config(self._tracing_config)
             self._update_created_session(parsed.session)
@@ -1209,7 +1214,9 @@ async def _handle_ws_event(self, event: dict[str, Any]):
             parsed.type == "response.output_item.added"
             or parsed.type == "response.output_item.done"
         ):
-            await self._handle_output_item(parsed.item)
+            await self._handle_output_item(
+                parsed.item, response_id=getattr(parsed, "response_id", None)
+            )
         elif parsed.type == "input_audio_buffer.timeout_triggered":
             await self._emit_event(
                 RealtimeModelInputAudioTimeoutTriggeredEvent(

src/agents/realtime/session.py

@@ -66,6 +66,7 @@
 from .model_inputs import (
     RealtimeModelSendAudio,
     RealtimeModelSendInterrupt,
+    RealtimeModelSendRawMessage,
     RealtimeModelSendSessionUpdate,
     RealtimeModelSendToolOutput,
     RealtimeModelSendUserInput,
@@ -176,6 +177,14 @@ def __init__(
         self._tool_call_tasks: set[asyncio.Task[Any]] = set()
         self._async_tool_calls: bool = bool(self._run_config.get("async_tool_calls", True))
 
+        # Coalesce response.create across parallel tool calls emitted in the same model response.
+        # Each entry tracks call_ids still pending and whether the model has signalled the end
+        # of the turn (response.done). Only the last completing tool call for a finished turn
+        # requests a new response so the OpenAI Realtime API never sees overlapping
+        # response.create events that would error with conversation_already_has_active_response.
+        self._tool_calls_by_response: dict[str, set[str]] = {}
+        self._turn_ended_responses: set[str] = set()
+
     @property
     def model(self) -> RealtimeModel:
         """Access the underlying model for adding listeners or other direct interaction."""
@@ -278,6 +287,7 @@ async def on_event(self, event: RealtimeModelEvent) -> None:
             await self._put_event(RealtimeError(info=self._event_info, error=event.error))
         elif event.type == "function_call":
             agent_snapshot = self._current_agent
+            self._register_pending_tool_call(event)
             if self._async_tool_calls:
                 self._enqueue_tool_call_task(event, agent_snapshot)
             else:
@@ -429,6 +439,8 @@ async def on_event(self, event: RealtimeModelEvent) -> None:
             self._item_transcripts.clear()
             self._item_guardrail_run_counts.clear()
 
+            await self._mark_turn_ended(event.response_id)
+
             await self._put_event(
                 RealtimeAgentEndEvent(
                     agent=self._current_agent,
@@ -556,11 +568,12 @@ async def _send_tool_rejection(
             tool=tool,
             call_id=event.call_id,
         )
+        start_response = self._consume_pending_tool_call(event)
         await self._model.send_event(
             RealtimeModelSendToolOutput(
                 tool_call=event,
                 output=rejection_message,
-                start_response=True,
+                start_response=start_response,
             )
         )
 
@@ -700,11 +713,12 @@ async def _handle_tool_call(
                 arguments=event.arguments,
             )
 
+            start_response = self._consume_pending_tool_call(event)
             await self._model.send_event(
                 RealtimeModelSendToolOutput(
                     tool_call=event,
                     output=_serialize_tool_output(result),
-                    start_response=True,
+                    start_response=start_response,
                 )
             )
 
@@ -763,6 +777,7 @@ async def _handle_tool_call(
 
             # Then send tool output to complete the handoff (this triggers a new response)
             transfer_message = handoff.get_transfer_message(result)
+            self._consume_pending_tool_call(event)
             await self._model.send_event(
                 RealtimeModelSendToolOutput(
                     tool_call=event,
@@ -772,6 +787,7 @@ async def _handle_tool_call(
             )
         else:
             error_message = f"Tool {event.name} not found"
+            self._consume_pending_tool_call(event)
             await self._model.send_event(
                 RealtimeModelSendToolOutput(
                     tool_call=event,
@@ -1065,6 +1081,71 @@ def _enqueue_tool_call_task(
         self._tool_call_tasks.add(task)
         task.add_done_callback(self._on_tool_call_task_done)
 
+    def _register_pending_tool_call(self, event: RealtimeModelToolCallEvent) -> None:
+        """Record a tool call so we can coalesce response.create per model response."""
+        response_id = event.response_id
+        if not response_id:
+            return
+        pending = self._tool_calls_by_response.setdefault(response_id, set())
+        pending.add(event.call_id)
+
+    def _consume_pending_tool_call(self, event: RealtimeModelToolCallEvent) -> bool:
+        """Mark a tool call as complete and return whether it should trigger response.create.
+
+        Returns True if this is the last pending tool call for a turn that has already ended,
+        meaning the caller should request a new response. Otherwise returns False so the
+        Realtime API never receives a response.create while another response is still active
+        or while other tool outputs for the same turn are still in flight.
+        """
+        response_id = event.response_id
+        if not response_id:
+            # Without a response id we can't coalesce, so fall back to the historical behavior
+            # of always requesting a response after every tool output.
+            return True
+
+        pending = self._tool_calls_by_response.get(response_id)
+        if pending is None:
+            # The function_call event arrived without going through on_event, or the bookkeeping
+            # has already been cleared. Be conservative and request a response.
+            return True
+
+        pending.discard(event.call_id)
+        if pending:
+            # Other tool outputs for the same turn are still in flight.
+            return False
+
+        if response_id not in self._turn_ended_responses:
+            # The model hasn't finished emitting this turn yet, so more tool calls may still
+            # arrive. Wait for turn_ended to drive response.create.
+            return False
+
+        self._tool_calls_by_response.pop(response_id, None)
+        self._turn_ended_responses.discard(response_id)
+        return True
+
+    async def _mark_turn_ended(self, response_id: str | None) -> None:
+        """Record that the model finished a turn and trigger response.create if needed."""
+        if not response_id:
+            return
+        pending = self._tool_calls_by_response.get(response_id)
+        if pending is None:
+            # No tool calls were tracked for this response, nothing to coalesce.
+            return
+        if pending:
+            # Tool outputs are still in flight; the last one to finish will request the response.
+            self._turn_ended_responses.add(response_id)
+            return
+
+        # All tool outputs have already been sent with start_response=False, so we have to
+        # request a response ourselves now that the turn is complete.
+        self._tool_calls_by_response.pop(response_id, None)
+        self._turn_ended_responses.discard(response_id)
+        await self._model.send_event(
+            RealtimeModelSendRawMessage(
+                message={"type": "response.create"},
+            )
+        )
+
     def _on_tool_call_task_done(self, task: asyncio.Task[Any]) -> None:
         self._tool_call_tasks.discard(task)
 
@@ -1117,6 +1198,8 @@ async def _cleanup(self) -> None:
 
         # Clear pending approval tracking
         self._pending_tool_calls.clear()
+        self._tool_calls_by_response.clear()
+        self._turn_ended_responses.clear()
 
         # Mark as closed
         self._closed = True

tests/realtime/test_openai_realtime.py

@@ -1692,6 +1692,9 @@ async def test_handle_tool_call_event_success(self, model):
         assert tool_call_emitted.name == "get_weather"
         assert tool_call_emitted.arguments == '{"location": "San Francisco"}'
         assert tool_call_emitted.call_id == "call_123"
+        # response_id must be propagated so RealtimeSession can coalesce parallel tool
+        # calls per model response and avoid overlapping response.create events.
+        assert tool_call_emitted.response_id == "resp_789"
 
     @pytest.mark.asyncio
     async def test_audio_timing_calculation_accuracy(self, model):