diff --git a/dpgen2/superop/prep_run_calypso.py b/dpgen2/superop/prep_run_calypso.py
index d8bc686a..daa48143 100644
--- a/dpgen2/superop/prep_run_calypso.py
+++ b/dpgen2/superop/prep_run_calypso.py
@@ -58,10 +58,12 @@ def __init__(
         prep_caly_model_devi_op: Type[OP],
         run_caly_model_devi_op: Type[OP],
         expl_mode: str = "default",
-        prep_config: dict = normalize_step_dict({}),
-        run_config: dict = normalize_step_dict({}),
+        prep_config: Optional[dict] = None,
+        run_config: Optional[dict] = None,
         upload_python_packages: Optional[List[os.PathLike]] = None,
     ):
+        prep_config = normalize_step_dict({}) if prep_config is None else prep_config
+        run_config = normalize_step_dict({}) if run_config is None else run_config
         self._input_parameters = {
             "block_id": InputParameter(type=str, value=""),
             "expl_task_grp": InputParameter(),
diff --git a/dpgen2/superop/prep_run_diffcsp.py b/dpgen2/superop/prep_run_diffcsp.py
index c7978e10..c4d3bd87 100644
--- a/dpgen2/superop/prep_run_diffcsp.py
+++ b/dpgen2/superop/prep_run_diffcsp.py
@@ -53,10 +53,12 @@ def __init__(
         diffcsp_gen_op: Type[OP],
         prep_relax_op: Type[OP],
         run_relax_op: Type[OP],
-        prep_config: dict = normalize_step_dict({}),
-        run_config: dict = normalize_step_dict({}),
+        prep_config: Optional[dict] = None,
+        run_config: Optional[dict] = None,
         upload_python_packages: Optional[List[os.PathLike]] = None,
     ):
+        prep_config = normalize_step_dict({}) if prep_config is None else prep_config
+        run_config = normalize_step_dict({}) if run_config is None else run_config
         self._input_parameters = {
             "block_id": InputParameter(type=str, value=""),
             "expl_task_grp": InputParameter(),
diff --git a/dpgen2/superop/prep_run_dp_train.py b/dpgen2/superop/prep_run_dp_train.py
index 006ff562..0fd988e4 100644
--- a/dpgen2/superop/prep_run_dp_train.py
+++ b/dpgen2/superop/prep_run_dp_train.py
@@ -60,12 +60,14 @@ def __init__(
         name: str,
         prep_train_op: Type[OP],
         run_train_op: Type[RunDPTrain],
-        prep_config: dict = normalize_step_dict({}),
-        run_config: dict = normalize_step_dict({}),
+        prep_config: Optional[dict] = None,
+        run_config: Optional[dict] = None,
         upload_python_packages: Optional[List[os.PathLike]] = None,
         valid_data: Optional[S3Artifact] = None,
         optional_files: Optional[List[str]] = None,
     ):
+        prep_config = normalize_step_dict({}) if prep_config is None else prep_config
+        run_config = normalize_step_dict({}) if run_config is None else run_config
         self._input_parameters = {
             "block_id": InputParameter(type=str, value=""),
             "numb_models": InputParameter(type=int),
diff --git a/dpgen2/superop/prep_run_fp.py b/dpgen2/superop/prep_run_fp.py
index d8085ea3..6203e755 100644
--- a/dpgen2/superop/prep_run_fp.py
+++ b/dpgen2/superop/prep_run_fp.py
@@ -52,10 +52,12 @@ def __init__(
         name: str,
         prep_op: Type[OP],
         run_op: Type[OP],
-        prep_config: dict = normalize_step_dict({}),
-        run_config: dict = normalize_step_dict({}),
+        prep_config: Optional[dict] = None,
+        run_config: Optional[dict] = None,
         upload_python_packages: Optional[List[os.PathLike]] = None,
     ):
+        prep_config = normalize_step_dict({}) if prep_config is None else prep_config
+        run_config = normalize_step_dict({}) if run_config is None else run_config
         self._input_parameters = {
             "block_id": InputParameter(type=str, value=""),
             "fp_config": InputParameter(),
diff --git a/dpgen2/superop/prep_run_lmp.py b/dpgen2/superop/prep_run_lmp.py
index cc8e02c3..6b4de94a 100644
--- a/dpgen2/superop/prep_run_lmp.py
+++ b/dpgen2/superop/prep_run_lmp.py
@@ -52,10 +52,12 @@ def __init__(
         name: str,
         prep_op: Type[OP],
         run_op: Type[OP],
-        prep_config: dict = normalize_step_dict({}),
-        run_config: dict = normalize_step_dict({}),
+        prep_config: Optional[dict] = None,
+        run_config: Optional[dict] = None,
         upload_python_packages: Optional[List[os.PathLike]] = None,
     ):
+        prep_config = normalize_step_dict({}) if prep_config is None else prep_config
+        run_config = normalize_step_dict({}) if run_config is None else run_config
         self._input_parameters = {
             "block_id": InputParameter(type=str, value=""),
             "explore_config": InputParameter(),