openai[minor]: add image generation to responses api (#31424)

Does not support partial images during generation at the moment. Before
doing that I'd like to figure out how to specify the aggregation logic
without requiring changes in core.

---------

Co-authored-by: Chester Curme <chester.curme@gmail.com>

libs/partners/openai/langchain_openai/chat_models/base.py

@@ -118,6 +118,15 @@ global_ssl_context = ssl.create_default_context(cafile=certifi.where())
 
 _FUNCTION_CALL_IDS_MAP_KEY = "__openai_function_call_ids__"
 
+WellKnownTools = (
+    "file_search",
+    "web_search_preview",
+    "computer_use_preview",
+    "code_interpreter",
+    "mcp",
+    "image_generation",
+)
+
 
 def _convert_dict_to_message(_dict: Mapping[str, Any]) -> BaseMessage:
     """Convert a dictionary to a LangChain message.
@@ -1487,13 +1496,7 @@ class BaseChatOpenAI(BaseChatModel):
                         "type": "function",
                         "function": {"name": tool_choice},
                     }
-                elif tool_choice in (
+                elif tool_choice in WellKnownTools:
-                    "file_search",
-                    "web_search_preview",
-                    "computer_use_preview",
-                    "code_interpreter",
-                    "mcp",
-                ):
                     tool_choice = {"type": tool_choice}
                 # 'any' is not natively supported by OpenAI API.
                 # We support 'any' since other models use this instead of 'required'.
@@ -3050,6 +3053,13 @@ def _construct_responses_api_payload(
                 new_tools.append({"type": "function", **tool["function"]})
             else:
                 new_tools.append(tool)
+
+            if tool["type"] == "image_generation" and "partial_images" in tool:
+                raise NotImplementedError(
+                    "Partial image generation is not yet supported "
+                    "via the LangChain ChatOpenAI client. Please "
+                    "drop the 'partial_images' key from the image_generation tool."
+                )
         payload["tools"] = new_tools
     if tool_choice := payload.pop("tool_choice", None):
         # chat api: {"type": "function", "function": {"name": "..."}}
@@ -3139,6 +3149,7 @@ def _pop_summary_index_from_reasoning(reasoning: dict) -> dict:
 
 
 def _construct_responses_api_input(messages: Sequence[BaseMessage]) -> list:
+    """Construct the input for the OpenAI Responses API."""
     input_ = []
     for lc_msg in messages:
         msg = _convert_message_to_dict(lc_msg)
@@ -3191,6 +3202,7 @@ def _construct_responses_api_input(messages: Sequence[BaseMessage]) -> list:
             computer_calls = []
             code_interpreter_calls = []
             mcp_calls = []
+            image_generation_calls = []
             tool_outputs = lc_msg.additional_kwargs.get("tool_outputs", [])
             for tool_output in tool_outputs:
                 if tool_output.get("type") == "computer_call":
@@ -3199,10 +3211,22 @@ def _construct_responses_api_input(messages: Sequence[BaseMessage]) -> list:
                     code_interpreter_calls.append(tool_output)
                 elif tool_output.get("type") == "mcp_call":
                     mcp_calls.append(tool_output)
+                elif tool_output.get("type") == "image_generation_call":
+                    image_generation_calls.append(tool_output)
                 else:
                     pass
             input_.extend(code_interpreter_calls)
             input_.extend(mcp_calls)
+
+            # A previous image generation call can be referenced by ID
+
+            input_.extend(
+                [
+                    {"type": "image_generation_call", "id": image_generation_call["id"]}
+                    for image_generation_call in image_generation_calls
+                ]
+            )
+
             msg["content"] = msg.get("content") or []
             if lc_msg.additional_kwargs.get("refusal"):
                 if isinstance(msg["content"], str):
@@ -3489,6 +3513,7 @@ def _convert_responses_chunk_to_generation_chunk(
         "mcp_call",
         "mcp_list_tools",
         "mcp_approval_request",
+        "image_generation_call",
     ):
         additional_kwargs["tool_outputs"] = [
             chunk.item.model_dump(exclude_none=True, mode="json")
@@ -3516,6 +3541,9 @@ def _convert_responses_chunk_to_generation_chunk(
                 {"index": chunk.summary_index, "type": "summary_text", "text": ""}
             ]
         }
+    elif chunk.type == "response.image_generation_call.partial_image":
+        # Partial images are not supported yet.
+        pass
     elif chunk.type == "response.reasoning_summary_text.delta":
         additional_kwargs["reasoning"] = {
             "summary": [

libs/partners/openai/pyproject.toml

@@ -7,7 +7,7 @@ authors = []
 license = { text = "MIT" }
 requires-python = ">=3.9"
 dependencies = [
-    "langchain-core<1.0.0,>=0.3.61",
+    "langchain-core<1.0.0,>=0.3.63",
     "openai<2.0.0,>=1.68.2",
     "tiktoken<1,>=0.7",
 ]

libs/partners/openai/tests/integration_tests/chat_models/test_responses_api.py

@@ -12,6 +12,7 @@ from langchain_core.messages import (
     BaseMessage,
     BaseMessageChunk,
     HumanMessage,
+    MessageLikeRepresentation,
 )
 from pydantic import BaseModel
 from typing_extensions import TypedDict
@@ -452,3 +453,130 @@ def test_mcp_builtin() -> None:
     _ = llm_with_tools.invoke(
         [approval_message], previous_response_id=response.response_metadata["id"]
     )
+
+
+@pytest.mark.vcr()
+def test_image_generation_streaming() -> None:
+    """Test image generation streaming."""
+    llm = ChatOpenAI(model="gpt-4.1", use_responses_api=True)
+    tool = {
+        "type": "image_generation",
+        # For testing purposes let's keep the quality low, so the test runs faster.
+        "quality": "low",
+        "output_format": "jpeg",
+        "output_compression": 100,
+        "size": "1024x1024",
+    }
+
+    # Example tool output for an image
+    # {
+    #     "background": "opaque",
+    #     "id": "ig_683716a8ddf0819888572b20621c7ae4029ec8c11f8dacf8",
+    #     "output_format": "png",
+    #     "quality": "high",
+    #     "revised_prompt": "A fluffy, fuzzy cat sitting calmly, with soft fur, bright "
+    #     "eyes, and a cute, friendly expression. The background is "
+    #     "simple and light to emphasize the cat's texture and "
+    #     "fluffiness.",
+    #     "size": "1024x1024",
+    #     "status": "completed",
+    #     "type": "image_generation_call",
+    #     "result": # base64 encode image data
+    # }
+
+    expected_keys = {
+        "id",
+        "background",
+        "output_format",
+        "quality",
+        "result",
+        "revised_prompt",
+        "size",
+        "status",
+        "type",
+    }
+
+    full: Optional[BaseMessageChunk] = None
+    for chunk in llm.stream("Draw a random short word in green font.", tools=[tool]):
+        assert isinstance(chunk, AIMessageChunk)
+        full = chunk if full is None else full + chunk
+    complete_ai_message = cast(AIMessageChunk, full)
+    # At the moment, the streaming API does not pick up annotations fully.
+    # So the following check is commented out.
+    # _check_response(complete_ai_message)
+    tool_output = complete_ai_message.additional_kwargs["tool_outputs"][0]
+    assert set(tool_output.keys()).issubset(expected_keys)
+
+
+@pytest.mark.vcr()
+def test_image_generation_multi_turn() -> None:
+    """Test multi-turn editing of image generation by passing in history."""
+    # Test multi-turn
+    llm = ChatOpenAI(model="gpt-4.1", use_responses_api=True)
+    # Test invocation
+    tool = {
+        "type": "image_generation",
+        # For testing purposes let's keep the quality low, so the test runs faster.
+        "quality": "low",
+        "output_format": "jpeg",
+        "output_compression": 100,
+        "size": "1024x1024",
+    }
+    llm_with_tools = llm.bind_tools([tool])
+
+    chat_history: list[MessageLikeRepresentation] = [
+        {"role": "user", "content": "Draw a random short word in green font."}
+    ]
+    ai_message = llm_with_tools.invoke(chat_history)
+    _check_response(ai_message)
+    tool_output = ai_message.additional_kwargs["tool_outputs"][0]
+
+    # Example tool output for an image
+    # {
+    #     "background": "opaque",
+    #     "id": "ig_683716a8ddf0819888572b20621c7ae4029ec8c11f8dacf8",
+    #     "output_format": "png",
+    #     "quality": "high",
+    #     "revised_prompt": "A fluffy, fuzzy cat sitting calmly, with soft fur, bright "
+    #     "eyes, and a cute, friendly expression. The background is "
+    #     "simple and light to emphasize the cat's texture and "
+    #     "fluffiness.",
+    #     "size": "1024x1024",
+    #     "status": "completed",
+    #     "type": "image_generation_call",
+    #     "result": # base64 encode image data
+    # }
+
+    expected_keys = {
+        "id",
+        "background",
+        "output_format",
+        "quality",
+        "result",
+        "revised_prompt",
+        "size",
+        "status",
+        "type",
+    }
+
+    assert set(tool_output.keys()).issubset(expected_keys)
+
+    chat_history.extend(
+        [
+            # AI message with tool output
+            ai_message,
+            # New request
+            {
+                "role": "user",
+                "content": (
+                    "Now, change the font to blue. Keep the word and everything else "
+                    "the same."
+                ),
+            },
+        ]
+    )
+
+    ai_message2 = llm_with_tools.invoke(chat_history)
+    _check_response(ai_message2)
+    tool_output2 = ai_message2.additional_kwargs["tool_outputs"][0]
+    assert set(tool_output2.keys()).issubset(expected_keys)