diff --git a/pydantic_ai_slim/pydantic_ai/agent.py b/pydantic_ai_slim/pydantic_ai/agent.py
index 2871fa4e3..37854ae79 100644
--- a/pydantic_ai_slim/pydantic_ai/agent.py
+++ b/pydantic_ai_slim/pydantic_ai/agent.py
@@ -12,7 +12,7 @@
 
 from opentelemetry.trace import NoOpTracer, use_span
 from pydantic.json_schema import GenerateJsonSchema
-from typing_extensions import Literal, Never, TypeGuard, TypeVar, deprecated
+from typing_extensions import Literal, Never, TypeIs, TypeVar, deprecated
 
 from pydantic_graph import End, Graph, GraphRun, GraphRunContext
 from pydantic_graph._utils import get_event_loop
@@ -459,7 +459,7 @@ def iter(
         self,
         user_prompt: str | Sequence[_messages.UserContent] | None,
         *,
-        output_type: type[RunOutputDataT] | ToolOutput[RunOutputDataT] | None = None,
+        output_type: None = None,
         message_history: list[_messages.ModelMessage] | None = None,
         model: models.Model | models.KnownModelName | str | None = None,
         deps: AgentDepsT = None,
@@ -468,7 +468,23 @@ def iter(
         usage: _usage.Usage | None = None,
         infer_name: bool = True,
         **_deprecated_kwargs: Never,
-    ) -> AbstractAsyncContextManager[AgentRun[AgentDepsT, Any]]: ...
+    ) -> AbstractAsyncContextManager[AgentRun[AgentDepsT, OutputDataT]]: ...
+
+    @overload
+    def iter(
+        self,
+        user_prompt: str | Sequence[_messages.UserContent] | None,
+        *,
+        output_type: type[RunOutputDataT] | ToolOutput[RunOutputDataT],
+        message_history: list[_messages.ModelMessage] | None = None,
+        model: models.Model | models.KnownModelName | str | None = None,
+        deps: AgentDepsT = None,
+        model_settings: ModelSettings | None = None,
+        usage_limits: _usage.UsageLimits | None = None,
+        usage: _usage.Usage | None = None,
+        infer_name: bool = True,
+        **_deprecated_kwargs: Never,
+    ) -> AbstractAsyncContextManager[AgentRun[AgentDepsT, RunOutputDataT]]: ...
 
     @overload
     @deprecated('`result_type` is deprecated, use `output_type` instead.')
@@ -1614,7 +1630,7 @@ def _prepare_output_schema(
     @staticmethod
     def is_model_request_node(
         node: _agent_graph.AgentNode[T, S] | End[result.FinalResult[S]],
-    ) -> TypeGuard[_agent_graph.ModelRequestNode[T, S]]:
+    ) -> TypeIs[_agent_graph.ModelRequestNode[T, S]]:
         """Check if the node is a `ModelRequestNode`, narrowing the type if it is.
 
         This method preserves the generic parameters while narrowing the type, unlike a direct call to `isinstance`.
@@ -1624,7 +1640,7 @@ def is_model_request_node(
     @staticmethod
     def is_call_tools_node(
         node: _agent_graph.AgentNode[T, S] | End[result.FinalResult[S]],
-    ) -> TypeGuard[_agent_graph.CallToolsNode[T, S]]:
+    ) -> TypeIs[_agent_graph.CallToolsNode[T, S]]:
         """Check if the node is a `CallToolsNode`, narrowing the type if it is.
 
         This method preserves the generic parameters while narrowing the type, unlike a direct call to `isinstance`.
@@ -1634,7 +1650,7 @@ def is_call_tools_node(
     @staticmethod
     def is_user_prompt_node(
         node: _agent_graph.AgentNode[T, S] | End[result.FinalResult[S]],
-    ) -> TypeGuard[_agent_graph.UserPromptNode[T, S]]:
+    ) -> TypeIs[_agent_graph.UserPromptNode[T, S]]:
         """Check if the node is a `UserPromptNode`, narrowing the type if it is.
 
         This method preserves the generic parameters while narrowing the type, unlike a direct call to `isinstance`.
@@ -1644,7 +1660,7 @@ def is_user_prompt_node(
     @staticmethod
     def is_end_node(
         node: _agent_graph.AgentNode[T, S] | End[result.FinalResult[S]],
-    ) -> TypeGuard[End[result.FinalResult[S]]]:
+    ) -> TypeIs[End[result.FinalResult[S]]]:
         """Check if the node is a `End`, narrowing the type if it is.
 
         This method preserves the generic parameters while narrowing the type, unlike a direct call to `isinstance`.