diff --git a/src/openai/_utils/_transform.py b/src/openai/_utils/_transform.py
index 304fd12ffe..9f1e66ebb5 100644
--- a/src/openai/_utils/_transform.py
+++ b/src/openai/_utils/_transform.py
@@ -387,7 +387,7 @@ async def _async_transform_recursive(
         return data
 
     if isinstance(data, pydantic.BaseModel):
-        return model_dump(data, exclude_unset=True, mode="json")
+        return model_dump(data, exclude_unset=True, mode="json", exclude=getattr(data, "__api_exclude__", None))
 
     annotated_type = _get_annotated_type(annotation)
     if annotated_type is None:
diff --git a/tests/test_transform.py b/tests/test_transform.py
index 93f7ad8dd8..a6f2e6331b 100644
--- a/tests/test_transform.py
+++ b/tests/test_transform.py
@@ -357,6 +357,21 @@ async def test_pydantic_default_field(use_async: bool) -> None:
     assert cast(Any, await transform(model, Any, use_async)) == {"with_none_default": "bar", "with_str_default": "baz"}
 
 
+class ModelWithApiExcludedField(BaseModel):
+    foo: str
+    client_only: Union[str, None] = None
+
+    __api_exclude__ = {"client_only"}
+
+
+@parametrize
+@pytest.mark.asyncio
+async def test_pydantic_model_api_exclude(use_async: bool) -> None:
+    model = ModelWithApiExcludedField(foo="hello!", client_only="secret")
+    assert cast(Any, await transform(model, Any, use_async)) == {"foo": "hello!"}
+    assert cast(Any, await transform([model], List[ModelWithApiExcludedField], use_async)) == [{"foo": "hello!"}]
+
+
 class TypedDictIterableUnion(TypedDict):
     foo: Annotated[Union[Bar8, Iterable[Baz8]], PropertyInfo(alias="FOO")]