diff --git a/laborious/activities/opc.py b/laborious/activities/opc.py
index 52b56d9..852f701 100644
--- a/laborious/activities/opc.py
+++ b/laborious/activities/opc.py
@@ -269,7 +269,7 @@ class OPC(BaseActivity):
         return success, response_times
 
     @activity.defn(name='write_opc_data')
-    async def write_opc_data(self, input_data: dict[str, Any]) -> dict[Any, Any]:
+    async def write_opc_data(self, input_data: dict[str, Any]) -> tuple[dict[Any, Any], dict[str, dict[str, float | None]]]:
         """
         Write prediction and confidence data to OPC servers. The two writing
         operations are optional and independent of each other.
@@ -314,10 +314,7 @@ class OPC(BaseActivity):
                 metadata,
             )
 
-        return {
-            'data': self.process_confidence(data, success, metadata),
-            'metrics': metrics,
-        }
+        return self.process_confidence(data, success, metadata), metrics
 
     def process_confidence(
         self, data: DataFrame, success: bool, metadata: dict[str, Any]