feat(responses): add MCP argument streaming and content part events (#3136)

# What does this PR do?

Adds content part streaming events to the OpenAI-compatible Responses API to support more granular streaming of response content. This introduces:

1. New schema types for content parts: `OpenAIResponseContentPart` with variants for text output and refusals

2. New streaming event types:
   - `OpenAIResponseObjectStreamResponseContentPartAdded` for when content parts begin
   - `OpenAIResponseObjectStreamResponseContentPartDone` for when content parts complete

3. Implementation in the reference provider to emit these events during streaming responses. Also emits MCP arguments just like function call ones.


## Test Plan

Updated existing streaming tests to verify content part events are properly emitted

docs/_static/llama-stack-spec.html

@@ -8821,6 +8821,61 @@
                 "title": "OpenAIResponseOutputMessageMCPListTools",
                 "description": "MCP list tools output message containing available tools from an MCP server."
             },
+            "OpenAIResponseContentPart": {
+                "oneOf": [
+                    {
+                        "$ref": "#/components/schemas/OpenAIResponseContentPartOutputText"
+                    },
+                    {
+                        "$ref": "#/components/schemas/OpenAIResponseContentPartRefusal"
+                    }
+                ],
+                "discriminator": {
+                    "propertyName": "type",
+                    "mapping": {
+                        "output_text": "#/components/schemas/OpenAIResponseContentPartOutputText",
+                        "refusal": "#/components/schemas/OpenAIResponseContentPartRefusal"
+                    }
+                }
+            },
+            "OpenAIResponseContentPartOutputText": {
+                "type": "object",
+                "properties": {
+                    "type": {
+                        "type": "string",
+                        "const": "output_text",
+                        "default": "output_text"
+                    },
+                    "text": {
+                        "type": "string"
+                    }
+                },
+                "additionalProperties": false,
+                "required": [
+                    "type",
+                    "text"
+                ],
+                "title": "OpenAIResponseContentPartOutputText"
+            },
+            "OpenAIResponseContentPartRefusal": {
+                "type": "object",
+                "properties": {
+                    "type": {
+                        "type": "string",
+                        "const": "refusal",
+                        "default": "refusal"
+                    },
+                    "refusal": {
+                        "type": "string"
+                    }
+                },
+                "additionalProperties": false,
+                "required": [
+                    "type",
+                    "refusal"
+                ],
+                "title": "OpenAIResponseContentPartRefusal"
+            },
             "OpenAIResponseObjectStream": {
                 "oneOf": [
                     {
@@ -8877,6 +8932,12 @@
                     {
                         "$ref": "#/components/schemas/OpenAIResponseObjectStreamResponseMcpCallCompleted"
                     },
+                    {
+                        "$ref": "#/components/schemas/OpenAIResponseObjectStreamResponseContentPartAdded"
+                    },
+                    {
+                        "$ref": "#/components/schemas/OpenAIResponseObjectStreamResponseContentPartDone"
+                    },
                     {
                         "$ref": "#/components/schemas/OpenAIResponseObjectStreamResponseCompleted"
                     }
@@ -8902,6 +8963,8 @@
                         "response.mcp_call.in_progress": "#/components/schemas/OpenAIResponseObjectStreamResponseMcpCallInProgress",
                         "response.mcp_call.failed": "#/components/schemas/OpenAIResponseObjectStreamResponseMcpCallFailed",
                         "response.mcp_call.completed": "#/components/schemas/OpenAIResponseObjectStreamResponseMcpCallCompleted",
+                        "response.content_part.added": "#/components/schemas/OpenAIResponseObjectStreamResponseContentPartAdded",
+                        "response.content_part.done": "#/components/schemas/OpenAIResponseObjectStreamResponseContentPartDone",
                         "response.completed": "#/components/schemas/OpenAIResponseObjectStreamResponseCompleted"
                     }
                 }
@@ -8928,6 +8991,80 @@
                 "title": "OpenAIResponseObjectStreamResponseCompleted",
                 "description": "Streaming event indicating a response has been completed."
             },
+            "OpenAIResponseObjectStreamResponseContentPartAdded": {
+                "type": "object",
+                "properties": {
+                    "response_id": {
+                        "type": "string",
+                        "description": "Unique identifier of the response containing this content"
+                    },
+                    "item_id": {
+                        "type": "string",
+                        "description": "Unique identifier of the output item containing this content part"
+                    },
+                    "part": {
+                        "$ref": "#/components/schemas/OpenAIResponseContentPart",
+                        "description": "The content part that was added"
+                    },
+                    "sequence_number": {
+                        "type": "integer",
+                        "description": "Sequential number for ordering streaming events"
+                    },
+                    "type": {
+                        "type": "string",
+                        "const": "response.content_part.added",
+                        "default": "response.content_part.added",
+                        "description": "Event type identifier, always \"response.content_part.added\""
+                    }
+                },
+                "additionalProperties": false,
+                "required": [
+                    "response_id",
+                    "item_id",
+                    "part",
+                    "sequence_number",
+                    "type"
+                ],
+                "title": "OpenAIResponseObjectStreamResponseContentPartAdded",
+                "description": "Streaming event for when a new content part is added to a response item."
+            },
+            "OpenAIResponseObjectStreamResponseContentPartDone": {
+                "type": "object",
+                "properties": {
+                    "response_id": {
+                        "type": "string",
+                        "description": "Unique identifier of the response containing this content"
+                    },
+                    "item_id": {
+                        "type": "string",
+                        "description": "Unique identifier of the output item containing this content part"
+                    },
+                    "part": {
+                        "$ref": "#/components/schemas/OpenAIResponseContentPart",
+                        "description": "The completed content part"
+                    },
+                    "sequence_number": {
+                        "type": "integer",
+                        "description": "Sequential number for ordering streaming events"
+                    },
+                    "type": {
+                        "type": "string",
+                        "const": "response.content_part.done",
+                        "default": "response.content_part.done",
+                        "description": "Event type identifier, always \"response.content_part.done\""
+                    }
+                },
+                "additionalProperties": false,
+                "required": [
+                    "response_id",
+                    "item_id",
+                    "part",
+                    "sequence_number",
+                    "type"
+                ],
+                "title": "OpenAIResponseObjectStreamResponseContentPartDone",
+                "description": "Streaming event for when a content part is completed."
+            },
             "OpenAIResponseObjectStreamResponseCreated": {
                 "type": "object",
                 "properties": {

docs/_static/llama-stack-spec.yaml

@@ -6441,6 +6441,43 @@ components:
       title: OpenAIResponseOutputMessageMCPListTools
       description: >-
         MCP list tools output message containing available tools from an MCP server.
+    OpenAIResponseContentPart:
+      oneOf:
+        - $ref: '#/components/schemas/OpenAIResponseContentPartOutputText'
+        - $ref: '#/components/schemas/OpenAIResponseContentPartRefusal'
+      discriminator:
+        propertyName: type
+        mapping:
+          output_text: '#/components/schemas/OpenAIResponseContentPartOutputText'
+          refusal: '#/components/schemas/OpenAIResponseContentPartRefusal'
+    OpenAIResponseContentPartOutputText:
+      type: object
+      properties:
+        type:
+          type: string
+          const: output_text
+          default: output_text
+        text:
+          type: string
+      additionalProperties: false
+      required:
+        - type
+        - text
+      title: OpenAIResponseContentPartOutputText
+    OpenAIResponseContentPartRefusal:
+      type: object
+      properties:
+        type:
+          type: string
+          const: refusal
+          default: refusal
+        refusal:
+          type: string
+      additionalProperties: false
+      required:
+        - type
+        - refusal
+      title: OpenAIResponseContentPartRefusal
     OpenAIResponseObjectStream:
       oneOf:
         - $ref: '#/components/schemas/OpenAIResponseObjectStreamResponseCreated'
@@ -6461,6 +6498,8 @@ components:
         - $ref: '#/components/schemas/OpenAIResponseObjectStreamResponseMcpCallInProgress'
         - $ref: '#/components/schemas/OpenAIResponseObjectStreamResponseMcpCallFailed'
         - $ref: '#/components/schemas/OpenAIResponseObjectStreamResponseMcpCallCompleted'
+        - $ref: '#/components/schemas/OpenAIResponseObjectStreamResponseContentPartAdded'
+        - $ref: '#/components/schemas/OpenAIResponseObjectStreamResponseContentPartDone'
         - $ref: '#/components/schemas/OpenAIResponseObjectStreamResponseCompleted'
       discriminator:
         propertyName: type
@@ -6483,6 +6522,8 @@ components:
           response.mcp_call.in_progress: '#/components/schemas/OpenAIResponseObjectStreamResponseMcpCallInProgress'
           response.mcp_call.failed: '#/components/schemas/OpenAIResponseObjectStreamResponseMcpCallFailed'
           response.mcp_call.completed: '#/components/schemas/OpenAIResponseObjectStreamResponseMcpCallCompleted'
+          response.content_part.added: '#/components/schemas/OpenAIResponseObjectStreamResponseContentPartAdded'
+          response.content_part.done: '#/components/schemas/OpenAIResponseObjectStreamResponseContentPartDone'
           response.completed: '#/components/schemas/OpenAIResponseObjectStreamResponseCompleted'
     "OpenAIResponseObjectStreamResponseCompleted":
       type: object
@@ -6504,6 +6545,76 @@ components:
         OpenAIResponseObjectStreamResponseCompleted
       description: >-
         Streaming event indicating a response has been completed.
+    "OpenAIResponseObjectStreamResponseContentPartAdded":
+      type: object
+      properties:
+        response_id:
+          type: string
+          description: >-
+            Unique identifier of the response containing this content
+        item_id:
+          type: string
+          description: >-
+            Unique identifier of the output item containing this content part
+        part:
+          $ref: '#/components/schemas/OpenAIResponseContentPart'
+          description: The content part that was added
+        sequence_number:
+          type: integer
+          description: >-
+            Sequential number for ordering streaming events
+        type:
+          type: string
+          const: response.content_part.added
+          default: response.content_part.added
+          description: >-
+            Event type identifier, always "response.content_part.added"
+      additionalProperties: false
+      required:
+        - response_id
+        - item_id
+        - part
+        - sequence_number
+        - type
+      title: >-
+        OpenAIResponseObjectStreamResponseContentPartAdded
+      description: >-
+        Streaming event for when a new content part is added to a response item.
+    "OpenAIResponseObjectStreamResponseContentPartDone":
+      type: object
+      properties:
+        response_id:
+          type: string
+          description: >-
+            Unique identifier of the response containing this content
+        item_id:
+          type: string
+          description: >-
+            Unique identifier of the output item containing this content part
+        part:
+          $ref: '#/components/schemas/OpenAIResponseContentPart'
+          description: The completed content part
+        sequence_number:
+          type: integer
+          description: >-
+            Sequential number for ordering streaming events
+        type:
+          type: string
+          const: response.content_part.done
+          default: response.content_part.done
+          description: >-
+            Event type identifier, always "response.content_part.done"
+      additionalProperties: false
+      required:
+        - response_id
+        - item_id
+        - part
+        - sequence_number
+        - type
+      title: >-
+        OpenAIResponseObjectStreamResponseContentPartDone
+      description: >-
+        Streaming event for when a content part is completed.
     "OpenAIResponseObjectStreamResponseCreated":
       type: object
       properties:

llama_stack/apis/agents/openai_responses.py

@@ -623,6 +623,62 @@ class OpenAIResponseObjectStreamResponseMcpCallCompleted(BaseModel):
     type: Literal["response.mcp_call.completed"] = "response.mcp_call.completed"
 
 
+@json_schema_type
+class OpenAIResponseContentPartOutputText(BaseModel):
+    type: Literal["output_text"] = "output_text"
+    text: str
+    # TODO: add annotations, logprobs, etc.
+
+
+@json_schema_type
+class OpenAIResponseContentPartRefusal(BaseModel):
+    type: Literal["refusal"] = "refusal"
+    refusal: str
+
+
+OpenAIResponseContentPart = Annotated[
+    OpenAIResponseContentPartOutputText | OpenAIResponseContentPartRefusal,
+    Field(discriminator="type"),
+]
+register_schema(OpenAIResponseContentPart, name="OpenAIResponseContentPart")
+
+
+@json_schema_type
+class OpenAIResponseObjectStreamResponseContentPartAdded(BaseModel):
+    """Streaming event for when a new content part is added to a response item.
+
+    :param response_id: Unique identifier of the response containing this content
+    :param item_id: Unique identifier of the output item containing this content part
+    :param part: The content part that was added
+    :param sequence_number: Sequential number for ordering streaming events
+    :param type: Event type identifier, always "response.content_part.added"
+    """
+
+    response_id: str
+    item_id: str
+    part: OpenAIResponseContentPart
+    sequence_number: int
+    type: Literal["response.content_part.added"] = "response.content_part.added"
+
+
+@json_schema_type
+class OpenAIResponseObjectStreamResponseContentPartDone(BaseModel):
+    """Streaming event for when a content part is completed.
+
+    :param response_id: Unique identifier of the response containing this content
+    :param item_id: Unique identifier of the output item containing this content part
+    :param part: The completed content part
+    :param sequence_number: Sequential number for ordering streaming events
+    :param type: Event type identifier, always "response.content_part.done"
+    """
+
+    response_id: str
+    item_id: str
+    part: OpenAIResponseContentPart
+    sequence_number: int
+    type: Literal["response.content_part.done"] = "response.content_part.done"
+
+
 OpenAIResponseObjectStream = Annotated[
     OpenAIResponseObjectStreamResponseCreated
     | OpenAIResponseObjectStreamResponseOutputItemAdded
@@ -642,6 +698,8 @@ OpenAIResponseObjectStream = Annotated[
     | OpenAIResponseObjectStreamResponseMcpCallInProgress
     | OpenAIResponseObjectStreamResponseMcpCallFailed
     | OpenAIResponseObjectStreamResponseMcpCallCompleted
+    | OpenAIResponseObjectStreamResponseContentPartAdded
+    | OpenAIResponseObjectStreamResponseContentPartDone
     | OpenAIResponseObjectStreamResponseCompleted,
     Field(discriminator="type"),
 ]

llama_stack/providers/inline/agents/meta_reference/openai_responses.py

@@ -20,6 +20,7 @@ from llama_stack.apis.agents.openai_responses import (
     ListOpenAIResponseInputItem,
     ListOpenAIResponseObject,
     OpenAIDeleteResponseObject,
+    OpenAIResponseContentPartOutputText,
     OpenAIResponseInput,
     OpenAIResponseInputFunctionToolCallOutput,
     OpenAIResponseInputMessageContent,
@@ -32,9 +33,13 @@ from llama_stack.apis.agents.openai_responses import (
     OpenAIResponseObject,
     OpenAIResponseObjectStream,
     OpenAIResponseObjectStreamResponseCompleted,
+    OpenAIResponseObjectStreamResponseContentPartAdded,
+    OpenAIResponseObjectStreamResponseContentPartDone,
     OpenAIResponseObjectStreamResponseCreated,
     OpenAIResponseObjectStreamResponseFunctionCallArgumentsDelta,
     OpenAIResponseObjectStreamResponseFunctionCallArgumentsDone,
+    OpenAIResponseObjectStreamResponseMcpCallArgumentsDelta,
+    OpenAIResponseObjectStreamResponseMcpCallArgumentsDone,
     OpenAIResponseObjectStreamResponseMcpCallCompleted,
     OpenAIResponseObjectStreamResponseMcpCallFailed,
     OpenAIResponseObjectStreamResponseMcpCallInProgress,
@@ -475,6 +480,8 @@ class OpenAIResponsesImpl:
             message_item_id = f"msg_{uuid.uuid4()}"
             # Track tool call items for streaming events
             tool_call_item_ids: dict[int, str] = {}
+            # Track content parts for streaming events
+            content_part_emitted = False
 
             async for chunk in completion_result:
                 chat_response_id = chunk.id
@@ -483,6 +490,18 @@ class OpenAIResponsesImpl:
                 for chunk_choice in chunk.choices:
                     # Emit incremental text content as delta events
                     if chunk_choice.delta.content:
+                        # Emit content_part.added event for first text chunk
+                        if not content_part_emitted:
+                            content_part_emitted = True
+                            sequence_number += 1
+                            yield OpenAIResponseObjectStreamResponseContentPartAdded(
+                                response_id=response_id,
+                                item_id=message_item_id,
+                                part=OpenAIResponseContentPartOutputText(
+                                    text="",  # Will be filled incrementally via text deltas
+                                ),
+                                sequence_number=sequence_number,
+                            )
                         sequence_number += 1
                         yield OpenAIResponseObjectStreamResponseOutputTextDelta(
                             content_index=0,
@@ -529,16 +548,33 @@ class OpenAIResponsesImpl:
                                     sequence_number=sequence_number,
                                 )
 
-                            # Stream function call arguments as they arrive
+                            # Stream tool call arguments as they arrive (differentiate between MCP and function calls)
                             if tool_call.function and tool_call.function.arguments:
                                 tool_call_item_id = tool_call_item_ids[tool_call.index]
                                 sequence_number += 1
-                                yield OpenAIResponseObjectStreamResponseFunctionCallArgumentsDelta(
+
-                                    delta=tool_call.function.arguments,
+                                # Check if this is an MCP tool call
-                                    item_id=tool_call_item_id,
+                                is_mcp_tool = (
-                                    output_index=len(output_messages),
+                                    ctx.mcp_tool_to_server
-                                    sequence_number=sequence_number,
+                                    and tool_call.function.name
+                                    and tool_call.function.name in ctx.mcp_tool_to_server
                                 )
+                                if is_mcp_tool:
+                                    # Emit MCP-specific argument delta event
+                                    yield OpenAIResponseObjectStreamResponseMcpCallArgumentsDelta(
+                                        delta=tool_call.function.arguments,
+                                        item_id=tool_call_item_id,
+                                        output_index=len(output_messages),
+                                        sequence_number=sequence_number,
+                                    )
+                                else:
+                                    # Emit function call argument delta event
+                                    yield OpenAIResponseObjectStreamResponseFunctionCallArgumentsDelta(
+                                        delta=tool_call.function.arguments,
+                                        item_id=tool_call_item_id,
+                                        output_index=len(output_messages),
+                                        sequence_number=sequence_number,
+                                    )
 
                                 # Accumulate arguments for final response (only for subsequent chunks)
                                 if not is_new_tool_call:
@@ -546,27 +582,55 @@ class OpenAIResponsesImpl:
                                         response_tool_call.function.arguments or ""
                                     ) + tool_call.function.arguments
 
-            # Emit function_call_arguments.done events for completed tool calls
+            # Emit arguments.done events for completed tool calls (differentiate between MCP and function calls)
             for tool_call_index in sorted(chat_response_tool_calls.keys()):
                 tool_call_item_id = tool_call_item_ids[tool_call_index]
                 final_arguments = chat_response_tool_calls[tool_call_index].function.arguments or ""
+                tool_call_name = chat_response_tool_calls[tool_call_index].function.name
+
+                # Check if this is an MCP tool call
+                is_mcp_tool = ctx.mcp_tool_to_server and tool_call_name and tool_call_name in ctx.mcp_tool_to_server
                 sequence_number += 1
-                yield OpenAIResponseObjectStreamResponseFunctionCallArgumentsDone(
+                if is_mcp_tool:
-                    arguments=final_arguments,
+                    # Emit MCP-specific argument done event
-                    item_id=tool_call_item_id,
+                    yield OpenAIResponseObjectStreamResponseMcpCallArgumentsDone(
-                    output_index=len(output_messages),
+                        arguments=final_arguments,
-                    sequence_number=sequence_number,
+                        item_id=tool_call_item_id,
-                )
+                        output_index=len(output_messages),
+                        sequence_number=sequence_number,
+                    )
+                else:
+                    # Emit function call argument done event
+                    yield OpenAIResponseObjectStreamResponseFunctionCallArgumentsDone(
+                        arguments=final_arguments,
+                        item_id=tool_call_item_id,
+                        output_index=len(output_messages),
+                        sequence_number=sequence_number,
+                    )
 
             # Convert collected chunks to complete response
             if chat_response_tool_calls:
                 tool_calls = [chat_response_tool_calls[i] for i in sorted(chat_response_tool_calls.keys())]
-
-                # when there are tool calls, we need to clear the content
-                chat_response_content = []
             else:
                 tool_calls = None
 
+            # Emit content_part.done event if text content was streamed (before content gets cleared)
+            if content_part_emitted:
+                final_text = "".join(chat_response_content)
+                sequence_number += 1
+                yield OpenAIResponseObjectStreamResponseContentPartDone(
+                    response_id=response_id,
+                    item_id=message_item_id,
+                    part=OpenAIResponseContentPartOutputText(
+                        text=final_text,
+                    ),
+                    sequence_number=sequence_number,
+                )
+
+            # Clear content when there are tool calls (OpenAI spec behavior)
+            if chat_response_tool_calls:
+                chat_response_content = []
+
             assistant_message = OpenAIAssistantMessageParam(
                 content="".join(chat_response_content),
                 tool_calls=tool_calls,

tests/integration/non_ci/responses/test_responses.py

@@ -590,9 +590,17 @@ def test_response_streaming_multi_turn_tool_execution(compat_client, text_model_
         # Verify tool call streaming events are present
         chunk_types = [chunk.type for chunk in chunks]
 
-        # Should have function call arguments delta events for tool calls
+        # Should have function call or MCP arguments delta/done events for tool calls
-        delta_events = [chunk for chunk in chunks if chunk.type == "response.function_call_arguments.delta"]
+        delta_events = [
-        done_events = [chunk for chunk in chunks if chunk.type == "response.function_call_arguments.done"]
+            chunk
+            for chunk in chunks
+            if chunk.type in ["response.function_call_arguments.delta", "response.mcp_call.arguments.delta"]
+        ]
+        done_events = [
+            chunk
+            for chunk in chunks
+            if chunk.type in ["response.function_call_arguments.done", "response.mcp_call.arguments.done"]
+        ]
 
         # Should have output item events for tool calls
         item_added_events = [chunk for chunk in chunks if chunk.type == "response.output_item.added"]
@@ -606,8 +614,12 @@ def test_response_streaming_multi_turn_tool_execution(compat_client, text_model_
         assert len(chunks) > 10, f"Expected rich streaming with many events, got only {len(chunks)} chunks"
 
         # Since this test involves MCP tool calls, we should see streaming events
-        assert len(delta_events) > 0, f"Expected function_call_arguments.delta events, got chunk types: {chunk_types}"
+        assert len(delta_events) > 0, (
-        assert len(done_events) > 0, f"Expected function_call_arguments.done events, got chunk types: {chunk_types}"
+            f"Expected function_call_arguments.delta or mcp_call.arguments.delta events, got chunk types: {chunk_types}"
+        )
+        assert len(done_events) > 0, (
+            f"Expected function_call_arguments.done or mcp_call.arguments.done events, got chunk types: {chunk_types}"
+        )
 
         # Should have output item events for function calls
         assert len(item_added_events) > 0, f"Expected response.output_item.added events, got chunk types: {chunk_types}"
@@ -670,22 +682,32 @@ def test_response_streaming_multi_turn_tool_execution(compat_client, text_model_
             assert isinstance(done_event.output_index, int), "Output index should be integer"
             assert done_event.output_index >= 0, "Output index should be non-negative"
 
-        # Group function call argument events by item_id (these should have proper tracking)
+        # Group function call and MCP argument events by item_id (these should have proper tracking)
-        function_call_events_by_item_id = {}
+        argument_events_by_item_id = {}
         for chunk in chunks:
             if hasattr(chunk, "item_id") and chunk.type in [
                 "response.function_call_arguments.delta",
                 "response.function_call_arguments.done",
+                "response.mcp_call.arguments.delta",
+                "response.mcp_call.arguments.done",
             ]:
                 item_id = chunk.item_id
-                if item_id not in function_call_events_by_item_id:
+                if item_id not in argument_events_by_item_id:
-                    function_call_events_by_item_id[item_id] = []
+                    argument_events_by_item_id[item_id] = []
-                function_call_events_by_item_id[item_id].append(chunk)
+                argument_events_by_item_id[item_id].append(chunk)
 
-        for item_id, related_events in function_call_events_by_item_id.items():
+        for item_id, related_events in argument_events_by_item_id.items():
-            # Should have at least one delta and one done event for a complete function call
+            # Should have at least one delta and one done event for a complete tool call
-            delta_events = [e for e in related_events if e.type == "response.function_call_arguments.delta"]
+            delta_events = [
-            done_events = [e for e in related_events if e.type == "response.function_call_arguments.done"]
+                e
+                for e in related_events
+                if e.type in ["response.function_call_arguments.delta", "response.mcp_call.arguments.delta"]
+            ]
+            done_events = [
+                e
+                for e in related_events
+                if e.type in ["response.function_call_arguments.done", "response.mcp_call.arguments.done"]
+            ]
 
             assert len(delta_events) > 0, f"Item {item_id} should have at least one delta event"
             assert len(done_events) == 1, f"Item {item_id} should have exactly one done event"
@@ -694,6 +716,33 @@ def test_response_streaming_multi_turn_tool_execution(compat_client, text_model_
             for event in related_events:
                 assert event.item_id == item_id, f"Event should have consistent item_id {item_id}, got {event.item_id}"
 
+        # Verify content part events if they exist (for text streaming)
+        content_part_added_events = [chunk for chunk in chunks if chunk.type == "response.content_part.added"]
+        content_part_done_events = [chunk for chunk in chunks if chunk.type == "response.content_part.done"]
+
+        # Content part events should be paired (if any exist)
+        if len(content_part_added_events) > 0:
+            assert len(content_part_done_events) > 0, (
+                "Should have content_part.done events if content_part.added events exist"
+            )
+
+            # Verify content part event structure
+            for added_event in content_part_added_events:
+                assert hasattr(added_event, "response_id"), "Content part added event should have response_id"
+                assert hasattr(added_event, "item_id"), "Content part added event should have item_id"
+                assert hasattr(added_event, "part"), "Content part added event should have part"
+
+                # TODO: enable this after the client types are updated
+                # assert added_event.part.type == "output_text", "Content part should be an output_text"
+
+            for done_event in content_part_done_events:
+                assert hasattr(done_event, "response_id"), "Content part done event should have response_id"
+                assert hasattr(done_event, "item_id"), "Content part done event should have item_id"
+                assert hasattr(done_event, "part"), "Content part done event should have part"
+
+                # TODO: enable this after the client types are updated
+                # assert len(done_event.part.text) > 0, "Content part should have text when done"
+
         # Basic pairing check: each output_item.added should be followed by some activity
         # (but we can't enforce strict 1:1 pairing due to the complexity of multi-turn scenarios)
         assert len(item_added_events) > 0, "Should have at least one output_item.added event"

tests/unit/providers/agents/meta_reference/test_openai_responses.py

@@ -136,9 +136,12 @@ async def test_create_openai_response_with_string_input(openai_responses_impl, m
         input=input_text,
         model=model,
         temperature=0.1,
+        stream=True,  # Enable streaming to test content part events
     )
 
-    # Verify
+    # For streaming response, collect all chunks
+    chunks = [chunk async for chunk in result]
+
     mock_inference_api.openai_chat_completion.assert_called_once_with(
         model=model,
         messages=[OpenAIUserMessageParam(role="user", content="What is the capital of Ireland?", name=None)],
@@ -147,11 +150,32 @@ async def test_create_openai_response_with_string_input(openai_responses_impl, m
         stream=True,
         temperature=0.1,
     )
+
+    # Should have content part events for text streaming
+    # Expected: response.created, content_part.added, output_text.delta, content_part.done, response.completed
+    assert len(chunks) >= 4
+    assert chunks[0].type == "response.created"
+
+    # Check for content part events
+    content_part_added_events = [c for c in chunks if c.type == "response.content_part.added"]
+    content_part_done_events = [c for c in chunks if c.type == "response.content_part.done"]
+    text_delta_events = [c for c in chunks if c.type == "response.output_text.delta"]
+
+    assert len(content_part_added_events) >= 1, "Should have content_part.added event for text"
+    assert len(content_part_done_events) >= 1, "Should have content_part.done event for text"
+    assert len(text_delta_events) >= 1, "Should have text delta events"
+
+    # Verify final event is completion
+    assert chunks[-1].type == "response.completed"
+
+    # When streaming, the final response is in the last chunk
+    final_response = chunks[-1].response
+    assert final_response.model == model
+    assert len(final_response.output) == 1
+    assert isinstance(final_response.output[0], OpenAIResponseMessage)
+
     openai_responses_impl.responses_store.store_response_object.assert_called_once()
-    assert result.model == model
+    assert final_response.output[0].content[0].text == "Dublin"
-    assert len(result.output) == 1
-    assert isinstance(result.output[0], OpenAIResponseMessage)
-    assert result.output[0].content[0].text == "Dublin"
 
 
 async def test_create_openai_response_with_string_input_with_tools(openai_responses_impl, mock_inference_api):
@@ -272,6 +296,8 @@ async def test_create_openai_response_with_tool_call_type_none(openai_responses_
 
     # Check that we got the content from our mocked tool execution result
     chunks = [chunk async for chunk in result]
+
+    # Verify event types
     # Should have: response.created, output_item.added, function_call_arguments.delta,
     # function_call_arguments.done, output_item.done, response.completed
     assert len(chunks) == 6