diff --git a/riskqueue/modeling/artifacts.py b/riskqueue/modeling/artifacts.py
index 9173709..f1ec085 100644
--- a/riskqueue/modeling/artifacts.py
+++ b/riskqueue/modeling/artifacts.py
@@ -1,7 +1,7 @@
 from __future__ import annotations
 
 import json
-from dataclasses import asdict, dataclass
+from dataclasses import asdict, dataclass, field
 from datetime import UTC, datetime
 from pathlib import Path
 
@@ -17,7 +17,7 @@ class ModelMetadata:
     roc_auc: float
     brier: float
     decision_threshold: float
-    created_at: str = datetime.now(UTC).isoformat()
+    created_at: str = field(default_factory=lambda: datetime.now(UTC).isoformat())
 
 
 def save_artifact(model, metadata: ModelMetadata, directory: str | Path) -> None:
diff --git a/tests/test_artifacts.py b/tests/test_artifacts.py
new file mode 100644
index 0000000..047c0bf
--- /dev/null
+++ b/tests/test_artifacts.py
@@ -0,0 +1,16 @@
+from datetime import UTC, datetime
+from unittest.mock import patch
+
+from riskqueue.modeling.artifacts import ModelMetadata
+
+
+def test_model_metadata_records_each_creation_time():
+    first_time = datetime(2026, 1, 1, tzinfo=UTC)
+    second_time = datetime(2026, 1, 2, tzinfo=UTC)
+    with patch("riskqueue.modeling.artifacts.datetime") as clock:
+        clock.now.side_effect = [first_time, second_time]
+        first = ModelMetadata("v1", "logistic", 10, 0.1, 0.7, 0.2, 0.3)
+        second = ModelMetadata("v2", "logistic", 20, 0.2, 0.8, 0.1, 0.4)
+
+    assert first.created_at == first_time.isoformat()
+    assert second.created_at == second_time.isoformat()