diff --git a/libs/partners/openai/langchain_openai/chat_models/base.py b/libs/partners/openai/langchain_openai/chat_models/base.py
index d2ff16912dd..e23f9ac5d28 100644
--- a/libs/partners/openai/langchain_openai/chat_models/base.py
+++ b/libs/partners/openai/langchain_openai/chat_models/base.py
@@ -3764,7 +3764,7 @@ def _construct_responses_api_payload(
                     if payload.get("stream") and "partial_images" not in tool:
                         # OpenAI requires this parameter be set; we ignore it during
                         # streaming.
-                        tool["partial_images"] = 1
+                        tool = {**tool, "partial_images": 1}
                     else:
                         pass
 
diff --git a/libs/partners/openai/tests/unit_tests/chat_models/test_responses_stream.py b/libs/partners/openai/tests/unit_tests/chat_models/test_responses_stream.py
index 75d31cf5e54..d710e1b4c46 100644
--- a/libs/partners/openai/tests/unit_tests/chat_models/test_responses_stream.py
+++ b/libs/partners/openai/tests/unit_tests/chat_models/test_responses_stream.py
@@ -756,3 +756,38 @@ def test_responses_stream(output_version: str, expected_content: list[dict]) ->
         dumped = _strip_none(item.model_dump())
         _ = dumped.pop("status", None)
         assert dumped == payload["input"][idx]
+
+
+def test_responses_stream_with_image_generation_multiple_calls() -> None:
+    """Test that streaming with image_generation tool works across multiple calls.
+
+    Regression test: image_generation tool should not be mutated between calls,
+    which would cause NotImplementedError on subsequent invocations.
+    """
+    tools: list[dict[str, Any]] = [
+        {"type": "image_generation"},
+        {"type": "function", "name": "my_tool", "parameters": {}},
+    ]
+    llm = ChatOpenAI(
+        model="gpt-4o",
+        use_responses_api=True,
+        streaming=True,
+    )
+    llm_with_tools = llm.bind_tools(tools)
+
+    mock_client = MagicMock()
+
+    def mock_create(*args: Any, **kwargs: Any) -> MockSyncContextManager:
+        return MockSyncContextManager(responses_stream)
+
+    mock_client.responses.create = mock_create
+
+    # First call should work
+    with patch.object(llm, "root_client", mock_client):
+        chunks = list(llm_with_tools.stream("test"))
+        assert len(chunks) > 0
+
+    # Second call should also work (would fail before fix due to tool mutation)
+    with patch.object(llm, "root_client", mock_client):
+        chunks = list(llm_with_tools.stream("test again"))
+        assert len(chunks) > 0