diff --git a/pydantic_ai_slim/pydantic_ai/agent.py b/pydantic_ai_slim/pydantic_ai/agent.py
index 15b8684026..096341fdb8 100644
--- a/pydantic_ai_slim/pydantic_ai/agent.py
+++ b/pydantic_ai_slim/pydantic_ai/agent.py
@@ -592,7 +592,7 @@ def run_sync(
     @overload
     def run_stream(
         self,
-        user_prompt: str | Sequence[_messages.UserContent],
+        user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         result_type: None = None,
         message_history: list[_messages.ModelMessage] | None = None,
@@ -607,7 +607,7 @@ def run_stream(
     @overload
     def run_stream(
         self,
-        user_prompt: str | Sequence[_messages.UserContent],
+        user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         result_type: type[RunResultDataT],
         message_history: list[_messages.ModelMessage] | None = None,
@@ -622,7 +622,7 @@ def run_stream(
     @asynccontextmanager
     async def run_stream(  # noqa C901
         self,
-        user_prompt: str | Sequence[_messages.UserContent],
+        user_prompt: str | Sequence[_messages.UserContent] | None = None,
         *,
         result_type: type[RunResultDataT] | None = None,
         message_history: list[_messages.ModelMessage] | None = None,