diff --git a/burr/core/action.py b/burr/core/action.py
index eb6fceff..c42cff41 100644
--- a/burr/core/action.py
+++ b/burr/core/action.py
@@ -1511,14 +1511,15 @@ def pydantic(
         writes: List[str],
         state_input_type: Type["BaseModel"],
         state_output_type: Type["BaseModel"],
-        stream_type: Union[Type["BaseModel"], Type[dict]],
+        stream_type: Union[Type["BaseModel"], Type[dict], object],
         tags: Optional[List[str]] = None,
     ) -> Callable:
         """Creates a streaming action that uses pydantic models.
 
         :param reads: The fields this consumes from the state.
         :param writes: The fields this writes to the state.
-        :param stream_type: The pydantic model or dictionary type that is used to represent the partial results.
+        :param stream_type: The pydantic model, dictionary type, or a union of pydantic models
+            (e.g. ``ModelA | ModelB``) used to represent the partial results.
             Use a dict if you want this untyped.
         :param state_input_type: The pydantic model type that is used to represent the input state.
         :param state_output_type: The pydantic model type that is used to represent the output state.
diff --git a/burr/integrations/pydantic.py b/burr/integrations/pydantic.py
index 300cbb6a..75fb86b9 100644
--- a/burr/integrations/pydantic.py
+++ b/burr/integrations/pydantic.py
@@ -269,7 +269,7 @@ async def async_action_function(state: State, **kwargs) -> State:
     return decorator
 
 
-PartialType = Union[Type[pydantic.BaseModel], Type[dict]]
+PartialType = Union[Type[pydantic.BaseModel], Type[dict], object]
 
 PydanticStreamingActionFunctionSync = Callable[
     ..., Generator[Tuple[Union[pydantic.BaseModel, dict], Optional[pydantic.BaseModel]], None, None]
@@ -290,7 +290,7 @@ async def async_action_function(state: State, **kwargs) -> State:
 
 def _validate_and_extract_signature_types_streaming(
     fn: PydanticStreamingActionFunction,
-    stream_type: Optional[Union[Type[pydantic.BaseModel], Type[dict]]],
+    stream_type: Optional[Union[Type[pydantic.BaseModel], Type[dict], object]],
     state_input_type: Optional[Type[pydantic.BaseModel]] = None,
     state_output_type: Optional[Type[pydantic.BaseModel]] = None,
 ) -> Tuple[