diff --git a/pyproject.toml b/pyproject.toml
index 7145dff7b..6b294b3c7 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -1,6 +1,6 @@
 [project]
 name = "temporalio"
-version = "1.21.0"
+version = "1.21.1"
 description = "Temporal.io Python SDK"
 authors = [{ name = "Temporal Technologies Inc", email = "sdk@temporal.io" }]
 requires-python = ">=3.10"
diff --git a/temporalio/contrib/openai_agents/_openai_runner.py b/temporalio/contrib/openai_agents/_openai_runner.py
index a8065d207..7e7853fbd 100644
--- a/temporalio/contrib/openai_agents/_openai_runner.py
+++ b/temporalio/contrib/openai_agents/_openai_runner.py
@@ -98,9 +98,8 @@ async def run(
                 **kwargs,
             )
 
-        tool_types = typing.get_args(Tool)
         for t in starting_agent.tools:
-            if not isinstance(t, tool_types):
+            if callable(t):
                 raise ValueError(
                     "Provided tool is not a tool type. If using an activity, make sure to wrap it with openai_agents.workflow.activity_as_tool."
                 )
diff --git a/temporalio/service.py b/temporalio/service.py
index 4f9588897..465003628 100644
--- a/temporalio/service.py
+++ b/temporalio/service.py
@@ -23,7 +23,7 @@
 import temporalio.exceptions
 import temporalio.runtime
 
-__version__ = "1.21.0"
+__version__ = "1.21.1"
 
 ServiceRequest = TypeVar("ServiceRequest", bound=google.protobuf.message.Message)
 ServiceResponse = TypeVar("ServiceResponse", bound=google.protobuf.message.Message)
diff --git a/uv.lock b/uv.lock
index 76ce83f28..3dd385b88 100644
--- a/uv.lock
+++ b/uv.lock
@@ -2919,7 +2919,7 @@ wheels = [
 
 [[package]]
 name = "temporalio"
-version = "1.21.0"
+version = "1.21.1"
 source = { virtual = "." }
 dependencies = [
     { name = "nexus-rpc" },