diff --git a/deepdrivewe/api.py b/deepdrivewe/api.py
index d16efe1..6f04997 100644
--- a/deepdrivewe/api.py
+++ b/deepdrivewe/api.py
@@ -494,7 +494,7 @@ class WeightedEnsemble(BaseModel):
         description='The target states for the weighted ensemble.',
     )
     metadata: IterationMetadata = Field(
-        default=IterationMetadata,
+        default_factory=IterationMetadata,
         description='The metadata for the current iteration.',
     )
     cur_sims: list[SimMetadata] = Field(
@@ -527,7 +527,7 @@ def initialize_basis_states(
 
     @property
     def iteration(self) -> int:
-        """Return the current iteration of the weighted ensemble."""
+        """The current iteration of the weighted ensemble (1-indexed)."""
         return self.metadata.iteration_id
 
     def advance_iteration(