diff --git a/code_generation/meta_data.py b/code_generation/meta_data.py
index 17b426c7a..3564e2276 100644
--- a/code_generation/meta_data.py
+++ b/code_generation/meta_data.py
@@ -5,7 +5,6 @@
 # define dataclass for meta data
 
 from dataclasses import dataclass
-from typing import Optional
 
 from dataclasses_json import DataClassJsonMixin
 
@@ -15,19 +14,19 @@ class Attribute(DataClassJsonMixin):
     data_type: str
     names: str | list[str]
     description: str
-    nan_value: Optional[str] = None
+    nan_value: str | None = None
 
 
 @dataclass
 class AttributeClass(DataClassJsonMixin):
     name: str
     attributes: list[Attribute]
-    full_attributes: Optional[list[Attribute]] = None
-    base: Optional[str] = None
+    full_attributes: list[Attribute] | None = None
+    base: str | None = None
     is_template: bool = False
-    full_name: Optional[str] = None
-    specification_names: Optional[list[str]] = None
-    base_attributes: Optional[dict[str, list[Attribute]]] = None
+    full_name: str | None = None
+    specification_names: list[str] | None = None
+    base_attributes: dict[str, list[Attribute]] | None = None
 
 
 @dataclass
diff --git a/src/power_grid_model/_core/error_handling.py b/src/power_grid_model/_core/error_handling.py
index 98e231361..758156c97 100644
--- a/src/power_grid_model/_core/error_handling.py
+++ b/src/power_grid_model/_core/error_handling.py
@@ -7,7 +7,6 @@
 """
 
 import re
-from typing import Optional
 
 import numpy as np
 
@@ -115,7 +114,7 @@ def _interpret_error(message: str, decode_error: bool = True) -> PowerGridError:
     return PowerGridError(message)
 
 
-def find_error(batch_size: int = 1, decode_error: bool = True) -> Optional[RuntimeError]:
+def find_error(batch_size: int = 1, decode_error: bool = True) -> RuntimeError | None:
     """
     Check if there is an error and return it
 
@@ -171,7 +170,7 @@ def assert_no_error(batch_size: int = 1, decode_error: bool = True):
 
 def handle_errors(
     continue_on_batch_error: bool, batch_size: int = 1, decode_error: bool = True
-) -> Optional[PowerGridBatchError]:
+) -> PowerGridBatchError | None:
     """
     Handle any errors in the way that is specified.
 
@@ -184,10 +183,10 @@ def handle_errors(
         error: Any errors previously encountered, unless it was a batch error and continue_on_batch_error was True.
 
     Returns:
-        Optional[PowerGridBatchError]: None if there were no errors, or the previously encountered
-                                       error if it was a batch error and continue_on_batch_error was True.
+        PowerGridBatchError | None: None if there were no errors, or the previously encountered
+                                    error if it was a batch error and continue_on_batch_error was True.
     """
-    error: Optional[RuntimeError] = find_error(batch_size=batch_size, decode_error=decode_error)
+    error: RuntimeError | None = find_error(batch_size=batch_size, decode_error=decode_error)
     if error is None:
         return None
 
diff --git a/src/power_grid_model/_core/power_grid_core.py b/src/power_grid_model/_core/power_grid_core.py
index 1f1d5f06b..5495e749b 100644
--- a/src/power_grid_model/_core/power_grid_core.py
+++ b/src/power_grid_model/_core/power_grid_core.py
@@ -11,7 +11,7 @@
 from inspect import signature
 from itertools import chain
 from pathlib import Path
-from typing import Callable, Optional
+from typing import Callable
 
 from power_grid_model._core.index_integer import IdC, IdxC
 
@@ -206,7 +206,7 @@ class PowerGridCore:
     """
 
     _handle: HandlePtr
-    _instance: Optional["PowerGridCore"] = None
+    _instance: "PowerGridCore | None" = None
 
     # singleton of power grid core
     def __new__(cls, *args, **kwargs):
diff --git a/src/power_grid_model/_core/power_grid_dataset.py b/src/power_grid_model/_core/power_grid_dataset.py
index aa23052e8..92285cb8d 100644
--- a/src/power_grid_model/_core/power_grid_dataset.py
+++ b/src/power_grid_model/_core/power_grid_dataset.py
@@ -6,7 +6,7 @@
 Power grid model raw dataset handler
 """
 
-from typing import Any, Mapping, Optional
+from typing import Any, Mapping
 
 from power_grid_model._core.buffer_handling import (
     BufferProperties,
@@ -283,7 +283,7 @@ class CConstDataset:
     _const_dataset: ConstDatasetPtr
     _buffer_views: list[CBuffer]
 
-    def __new__(cls, data: Dataset, dataset_type: Optional[DatasetType] = None):
+    def __new__(cls, data: Dataset, dataset_type: DatasetType | None = None):
         instance = super().__new__(cls)
         instance._const_dataset = ConstDatasetPtr()
 
diff --git a/src/power_grid_model/_core/power_grid_model.py b/src/power_grid_model/_core/power_grid_model.py
index cc60f6864..d4ce2eff1 100644
--- a/src/power_grid_model/_core/power_grid_model.py
+++ b/src/power_grid_model/_core/power_grid_model.py
@@ -7,7 +7,7 @@
 """
 
 from enum import IntEnum
-from typing import Optional, Type
+from typing import Type
 
 import numpy as np
 
@@ -45,11 +45,11 @@ class PowerGridModel:
     """
 
     _model_ptr: ModelPtr
-    _all_component_count: Optional[dict[ComponentType, int]]
-    _batch_error: Optional[PowerGridBatchError]
+    _all_component_count: dict[ComponentType, int] | None
+    _batch_error: PowerGridBatchError | None
 
     @property
-    def batch_error(self) -> Optional[PowerGridBatchError]:
+    def batch_error(self) -> PowerGridBatchError | None:
         """
         Get the batch error object, if present
 
@@ -242,7 +242,7 @@ def _calculate_impl(  # pylint: disable=too-many-positional-arguments
         self,
         calculation_type: CalculationType,
         symmetric: bool,
-        update_data: Optional[Dataset],
+        update_data: Dataset | None,
         output_component_types: ComponentAttributeMapping,
         options: Options,
         continue_on_batch_error: bool,
@@ -310,7 +310,7 @@ def _calculate_power_flow(
         error_tolerance: float = 1e-8,
         max_iterations: int = 20,
         calculation_method: CalculationMethod | str = CalculationMethod.newton_raphson,
-        update_data: Optional[Dataset] = None,
+        update_data: Dataset | None = None,
         threading: int = -1,
         output_component_types: ComponentAttributeMapping = None,
         continue_on_batch_error: bool = False,
@@ -347,7 +347,7 @@ def _calculate_state_estimation(
         error_tolerance: float = 1e-8,
         max_iterations: int = 20,
         calculation_method: CalculationMethod | str = CalculationMethod.iterative_linear,
-        update_data: Optional[Dataset] = None,
+        update_data: Dataset | None = None,
         threading: int = -1,
         output_component_types: ComponentAttributeMapping = None,
         continue_on_batch_error: bool = False,
@@ -379,7 +379,7 @@ def _calculate_short_circuit(
         self,
         *,
         calculation_method: CalculationMethod | str = CalculationMethod.iec60909,
-        update_data: Optional[Dataset] = None,
+        update_data: Dataset | None = None,
         threading: int = -1,
         output_component_types: ComponentAttributeMapping = None,
         continue_on_batch_error: bool = False,
@@ -416,7 +416,7 @@ def calculate_power_flow(
         error_tolerance: float = 1e-8,
         max_iterations: int = 20,
         calculation_method: CalculationMethod | str = CalculationMethod.newton_raphson,
-        update_data: Optional[dict[str, np.ndarray | dict[str, np.ndarray]] | Dataset] = None,
+        update_data: dict[str, np.ndarray | dict[str, np.ndarray]] | Dataset | None = None,
         threading: int = -1,
         output_component_types: ComponentAttributeMapping = None,
         continue_on_batch_error: bool = False,
@@ -514,7 +514,7 @@ def calculate_state_estimation(
         error_tolerance: float = 1e-8,
         max_iterations: int = 20,
         calculation_method: CalculationMethod | str = CalculationMethod.iterative_linear,
-        update_data: Optional[dict[str, np.ndarray | dict[str, np.ndarray]] | Dataset] = None,
+        update_data: dict[str, np.ndarray | dict[str, np.ndarray]] | Dataset | None = None,
         threading: int = -1,
         output_component_types: ComponentAttributeMapping = None,
         continue_on_batch_error: bool = False,
@@ -604,7 +604,7 @@ def calculate_short_circuit(
         self,
         *,
         calculation_method: CalculationMethod | str = CalculationMethod.iec60909,
-        update_data: Optional[dict[str, np.ndarray | dict[str, np.ndarray]] | Dataset] = None,
+        update_data: dict[str, np.ndarray | dict[str, np.ndarray]] | Dataset | None = None,
         threading: int = -1,
         output_component_types: ComponentAttributeMapping = None,
         continue_on_batch_error: bool = False,
diff --git a/src/power_grid_model/_utils.py b/src/power_grid_model/_utils.py
index 6f241fb2a..4dfbfeb54 100644
--- a/src/power_grid_model/_utils.py
+++ b/src/power_grid_model/_utils.py
@@ -11,7 +11,7 @@
 """
 
 from copy import deepcopy
-from typing import Optional, Sequence, cast
+from typing import Sequence, cast
 
 import numpy as np
 
@@ -218,8 +218,6 @@ def _split_numpy_array_in_batches(
 
     Args:
         data: A 1D or 2D Numpy structured array. A 1D array is a single table / batch, a 2D array is a batch per table.
-        component: The name of the component to which the data belongs; only used for errors.
-        attribute [optional]: The name of the attribute to which the data belongs; only used for errors.
 
     Returns:
         A list with a single numpy structured array per batch
@@ -239,7 +237,6 @@ def split_dense_batch_data_in_batches(
 
     Args:
         data: A 1D or 2D Numpy structured array. A 1D array is a single table / batch, a 2D array is a batch per table.
-        component: The name of the component to which the data belongs, only used for errors.
         batch_size: size of batch
 
     Returns:
@@ -326,7 +323,7 @@ def convert_dataset_to_python_dataset(data: Dataset) -> PythonDataset:
 
     # Check if the dataset is a single dataset or batch dataset
     # It is batch dataset if it is 2D array or a indptr/data structure
-    is_batch: Optional[bool] = None
+    is_batch: bool | None = None
     for component, array in data.items():
         is_dense_batch = isinstance(array, np.ndarray) and array.ndim == 2
         is_sparse_batch = isinstance(array, dict) and "indptr" in array and "data" in array
diff --git a/src/power_grid_model/utils.py b/src/power_grid_model/utils.py
index c724e0ca9..400f444aa 100644
--- a/src/power_grid_model/utils.py
+++ b/src/power_grid_model/utils.py
@@ -11,7 +11,7 @@
 import tempfile
 import warnings
 from pathlib import Path
-from typing import Optional, cast as cast_type
+from typing import cast as cast_type
 
 import numpy as np
 
@@ -142,9 +142,9 @@ def json_deserialize_from_file(
 def json_serialize_to_file(
     file_path: Path,
     data: Dataset,
-    dataset_type: Optional[DatasetType] = None,
+    dataset_type: DatasetType | None = None,
     use_compact_list: bool = False,
-    indent: Optional[int] = 2,
+    indent: int | None = 2,
 ):
     """
     Export JSON data in most recent format.
@@ -189,7 +189,7 @@ def msgpack_deserialize_from_file(
 
 
 def msgpack_serialize_to_file(
-    file_path: Path, data: Dataset, dataset_type: Optional[DatasetType] = None, use_compact_list: bool = False
+    file_path: Path, data: Dataset, dataset_type: DatasetType | None = None, use_compact_list: bool = False
 ):
     """
     Export msgpack data in most recent format.
@@ -234,7 +234,7 @@ def import_json_data(json_file: Path, data_type: str, *args, **kwargs) -> Datase
 
 
 def export_json_data(
-    json_file: Path, data: Dataset, indent: Optional[int] = 2, compact: bool = False, use_deprecated_format: bool = True
+    json_file: Path, data: Dataset, indent: int | None = 2, compact: bool = False, use_deprecated_format: bool = True
 ):
     """
     [deprecated] Export json data in a deprecated serialization format.
@@ -268,7 +268,7 @@ def export_json_data(
 
 
 def _compatibility_deprecated_export_json_data(
-    json_file: Path, data: Dataset, indent: Optional[int] = 2, compact: bool = False
+    json_file: Path, data: Dataset, indent: int | None = 2, compact: bool = False
 ):
     serialized_data = json_serialize(data=data, use_compact_list=compact, indent=-1 if indent is None else indent)
     old_format_serialized_data = json.dumps(json.loads(serialized_data)["data"])
diff --git a/src/power_grid_model/validation/assertions.py b/src/power_grid_model/validation/assertions.py
index 862e45cfe..23ce75a08 100644
--- a/src/power_grid_model/validation/assertions.py
+++ b/src/power_grid_model/validation/assertions.py
@@ -6,8 +6,6 @@
 Helper functions to assert valid data. They basically call validate_input_data or validate_batch_data and raise a
 ValidationException if the validation results in one or more errors.
 """
-from typing import Optional
-
 from power_grid_model.data_types import BatchDataset, SingleDataset
 from power_grid_model.enum import CalculationType
 from power_grid_model.validation.errors import ValidationError
@@ -31,7 +29,7 @@ def __str__(self):
 
 
 def assert_valid_input_data(
-    input_data: SingleDataset, calculation_type: Optional[CalculationType] = None, symmetric: bool = True
+    input_data: SingleDataset, calculation_type: CalculationType | None = None, symmetric: bool = True
 ):
     """
     Validates the entire input dataset:
@@ -60,7 +58,7 @@ def assert_valid_input_data(
 def assert_valid_batch_data(
     input_data: SingleDataset,
     update_data: BatchDataset,
-    calculation_type: Optional[CalculationType] = None,
+    calculation_type: CalculationType | None = None,
     symmetric: bool = True,
 ):
     """
diff --git a/src/power_grid_model/validation/errors.py b/src/power_grid_model/validation/errors.py
index 57c8488aa..840f1794e 100644
--- a/src/power_grid_model/validation/errors.py
+++ b/src/power_grid_model/validation/errors.py
@@ -8,7 +8,7 @@
 import re
 from abc import ABC
 from enum import Enum
-from typing import Any, Iterable, Optional, Type
+from typing import Any, Iterable, Type
 
 from power_grid_model import ComponentType
 
@@ -32,18 +32,18 @@ class ValidationError(ABC):
 
     """
 
-    component: Optional[ComponentType | list[ComponentType]] = None
+    component: ComponentType | list[ComponentType] | None = None
     """
     The component, or components, to which the error applies.
     """
 
-    field: Optional[str | list[str] | list[tuple[ComponentType, str]]] = None
+    field: str | list[str] | list[tuple[ComponentType, str]] | None = None
     """
     The field, or fields, to which the error applies. A field can also be a tuple (component, field) when multiple
     components are being addressed.
     """
 
-    ids: Optional[list[int] | list[tuple[ComponentType, int]]] = None
+    ids: list[int] | list[tuple[ComponentType, int]] | None = None
     """
     The object identifiers to which the error applies. A field object identifier can also be a tuple (component, id)
     when multiple components are being addressed.
@@ -79,7 +79,7 @@ def _unpack(field: str | tuple[ComponentType, str]) -> str:
             return self._delimiter.join(_unpack(field) for field in self.field)
         return _unpack(self.field) if self.field else str(self.field)
 
-    def get_context(self, id_lookup: Optional[list[str] | dict[int, str]] = None) -> dict[str, Any]:
+    def get_context(self, id_lookup: list[str] | dict[int, str] | None = None) -> dict[str, Any]:
         """
         Returns a dictionary that supplies (human readable) information about this error. Each member variable is
         included in the dictionary. If a function {field_name}_str() exists, the value is overwritten by that function.
@@ -129,9 +129,9 @@ class SingleFieldValidationError(ValidationError):
     _message = "Field {field} is not valid for {n} {objects}."
     component: ComponentType
     field: str
-    ids: Optional[list[int]]
+    ids: list[int] | None
 
-    def __init__(self, component: ComponentType, field: str, ids: Optional[Iterable[int]]):
+    def __init__(self, component: ComponentType, field: str, ids: Iterable[int] | None):
         """
         Args:
             component: Component name
@@ -325,9 +325,9 @@ def __init__(  # pylint: disable=too-many-arguments
         self,
         component: ComponentType,
         field: str,
-        ids: Optional[list[int]] = None,
-        ref_components: Optional[ComponentType | list[ComponentType]] = None,
-        filters: Optional[dict[str, Any]] = None,
+        ids: list[int] | None = None,
+        ref_components: ComponentType | list[ComponentType] | None = None,
+        filters: dict[str, Any] | None = None,
     ):
         # pylint: disable=too-many-positional-arguments
         super().__init__(component=component, field=field, ids=ids)
diff --git a/src/power_grid_model/validation/rules.py b/src/power_grid_model/validation/rules.py
index b506fe1ad..6f603b4a2 100644
--- a/src/power_grid_model/validation/rules.py
+++ b/src/power_grid_model/validation/rules.py
@@ -35,7 +35,7 @@
 
 """
 from enum import Enum
-from typing import Any, Callable, Optional, Type, TypeVar
+from typing import Any, Callable, Type, TypeVar
 
 import numpy as np
 
@@ -103,7 +103,7 @@ def all_greater_than_or_equal_to_zero(
     data: SingleDataset,
     component: ComponentType,
     field: str,
-    default_value: Optional[np.ndarray | int | float] = None,
+    default_value: np.ndarray | int | float | None = None,
 ) -> list[NotGreaterOrEqualError]:
     """
     Check that for all records of a particular type of component, the values in the 'field' column are greater than,
@@ -113,7 +113,7 @@ def all_greater_than_or_equal_to_zero(
         data (SingleDataset): The input/update data set for all components
         component (ComponentType) The component of interest
         field (str): The field of interest
-        default_value (Optional[np.ndarray | int | float], optional): Some values are not required, but will
+        default_value (np.ndarray | int | float | None, optional): Some values are not required, but will
             receive a default value in the C++ core. To do a proper input validation, these default values should be
             included in the validation. It can be a fixed value for the entire column (int/float) or be different for
             each element (np.ndarray).
@@ -156,7 +156,7 @@ def all_greater_or_equal(
     component: ComponentType,
     field: str,
     ref_value: int | float | str,
-    default_value: Optional[np.ndarray | int | float] = None,
+    default_value: np.ndarray | int | float | None = None,
 ) -> list[NotGreaterOrEqualError]:
     """
     Check that for all records of a particular type of component, the values in the 'field' column are greater than,
@@ -249,7 +249,7 @@ def all_between(  # pylint: disable=too-many-positional-arguments
     field: str,
     ref_value_1: int | float | str,
     ref_value_2: int | float | str,
-    default_value: Optional[np.ndarray | int | float] = None,
+    default_value: np.ndarray | int | float | None = None,
 ) -> list[NotBetweenError]:
     """
     Check that for all records of a particular type of component, the values in the 'field' column are (exclusively)
@@ -290,8 +290,8 @@ def all_between_or_at(  # pylint: disable=too-many-positional-arguments
     field: str,
     ref_value_1: int | float | str,
     ref_value_2: int | float | str,
-    default_value_1: Optional[np.ndarray | int | float] = None,
-    default_value_2: Optional[np.ndarray | int | float] = None,
+    default_value_1: np.ndarray | int | float | None = None,
+    default_value_2: np.ndarray | int | float | None = None,
 ) -> list[NotBetweenOrAtError]:
     """
     Check that for all records of a particular type of component, the values in the 'field' column are inclusively
@@ -341,8 +341,8 @@ def none_match_comparison(  # pylint: disable=too-many-arguments
     compare_fn: Callable,
     ref_value: ComparisonError.RefType,
     error: Type[CompError] = ComparisonError,  # type: ignore
-    default_value_1: Optional[np.ndarray | int | float] = None,
-    default_value_2: Optional[np.ndarray | int | float] = None,
+    default_value_1: np.ndarray | int | float | None = None,
+    default_value_2: np.ndarray | int | float | None = None,
 ) -> list[CompError]:
     # pylint: disable=too-many-positional-arguments
     """
@@ -719,7 +719,7 @@ def ids_valid_in_update_data_set(
     return []
 
 
-def all_finite(data: SingleDataset, exceptions: Optional[dict[ComponentType, list[str]]] = None) -> list[InfinityError]:
+def all_finite(data: SingleDataset, exceptions: dict[ComponentType, list[str]] | None = None) -> list[InfinityError]:
     """
     Check that for all records in all component, the values in all columns are finite value, i.e. float values other
     than inf, or -inf. Nan values are ignored, as in all other comparison functions. You can use non_missing() to
diff --git a/src/power_grid_model/validation/utils.py b/src/power_grid_model/validation/utils.py
index 2d2df85b8..247031e79 100644
--- a/src/power_grid_model/validation/utils.py
+++ b/src/power_grid_model/validation/utils.py
@@ -6,7 +6,7 @@
 Utilities used for validation. Only errors_to_string() is intended for end users.
 """
 import re
-from typing import Any, Optional, cast
+from typing import Any, cast
 
 import numpy as np
 
@@ -157,7 +157,7 @@ def errors_to_string(
     errors: list[ValidationError] | dict[int, list[ValidationError]] | None,
     name: str = "the data",
     details: bool = False,
-    id_lookup: Optional[list[str] | dict[int, str]] = None,
+    id_lookup: list[str] | dict[int, str] | None = None,
 ) -> str:
     """
     Convert a set of errors (list or dict) to a human readable string representation.
@@ -198,7 +198,7 @@ def _nan_type(component: ComponentTypeLike, field: str, data_type: DatasetType =
     return power_grid_meta_data[data_type][component].nans[field]
 
 
-def _get_indexer(source: np.ndarray, target: np.ndarray, default_value: Optional[int] = None) -> np.ndarray:
+def _get_indexer(source: np.ndarray, target: np.ndarray, default_value: int | None = None) -> np.ndarray:
     """
     Given array of values from a source and a target dataset.
     Find the position of each value in the target dataset in the context of the source dataset.
@@ -214,7 +214,7 @@ def _get_indexer(source: np.ndarray, target: np.ndarray, default_value: Optional
     Args:
         source: array of values in the source dataset
         target: array of values in the target dataset
-        default_value: Optional. the default index to provide for target values not in source
+        default_value (optional): the default index to provide for target values not in source
 
     Returns:
         np.ndarray: array of positions of the values from target dataset in the source dataset
diff --git a/src/power_grid_model/validation/validation.py b/src/power_grid_model/validation/validation.py
index 10dba4a2e..5e9fca790 100644
--- a/src/power_grid_model/validation/validation.py
+++ b/src/power_grid_model/validation/validation.py
@@ -14,7 +14,7 @@
 import copy
 from collections.abc import Sized as ABCSized
 from itertools import chain
-from typing import Optional, cast
+from typing import cast
 
 import numpy as np
 
@@ -69,8 +69,8 @@
 
 
 def validate_input_data(
-    input_data: SingleDataset, calculation_type: Optional[CalculationType] = None, symmetric: bool = True
-) -> Optional[list[ValidationError]]:
+    input_data: SingleDataset, calculation_type: CalculationType | None = None, symmetric: bool = True
+) -> list[ValidationError] | None:
     """
     Validates the entire input dataset:
 
@@ -108,9 +108,9 @@ def validate_input_data(
 def validate_batch_data(
     input_data: SingleDataset,
     update_data: BatchDataset,
-    calculation_type: Optional[CalculationType] = None,
+    calculation_type: CalculationType | None = None,
     symmetric: bool = True,
-) -> Optional[dict[int, list[ValidationError]]]:
+) -> dict[int, list[ValidationError]] | None:
     """
     The input dataset is validated:
 
@@ -285,7 +285,7 @@ def _process_power_sigma_in_list(_sensor_mask, _power_sigma, _p_sigma, _q_sigma)
 
 
 def validate_required_values(
-    data: SingleDataset, calculation_type: Optional[CalculationType] = None, symmetric: bool = True
+    data: SingleDataset, calculation_type: CalculationType | None = None, symmetric: bool = True
 ) -> list[MissingValueError]:
     """
     Checks if all required data is available.
@@ -451,7 +451,7 @@ def process_nested_items(component, items, data, results):
     return list(chain(*results))
 
 
-def validate_values(data: SingleDataset, calculation_type: Optional[CalculationType] = None) -> list[ValidationError]:
+def validate_values(data: SingleDataset, calculation_type: CalculationType | None = None) -> list[ValidationError]:
     """
     For each component supplied in the data, call the appropriate validation function
 
diff --git a/tests/unit/test_serialization.py b/tests/unit/test_serialization.py
index e7015bcba..c805c3881 100644
--- a/tests/unit/test_serialization.py
+++ b/tests/unit/test_serialization.py
@@ -3,7 +3,7 @@
 # SPDX-License-Identifier: MPL-2.0
 
 import json
-from typing import Any, Mapping, Optional
+from typing import Any, Mapping
 
 import msgpack
 import numpy as np
@@ -16,7 +16,7 @@
 from power_grid_model.utils import json_deserialize, json_serialize, msgpack_deserialize, msgpack_serialize
 
 
-def to_json(data, raw_buffer: bool = False, indent: Optional[int] = None):
+def to_json(data, raw_buffer: bool = False, indent: int | None = None):
     indent = None if indent is None or indent < 0 else indent
     separators = (",", ":") if indent is None else None
     result = json.dumps(data, indent=indent, separators=separators)
diff --git a/tests/unit/utils.py b/tests/unit/utils.py
index 5f1d19004..6de4a7429 100644
--- a/tests/unit/utils.py
+++ b/tests/unit/utils.py
@@ -6,7 +6,7 @@
 import os
 import re
 from pathlib import Path
-from typing import Any, Optional
+from typing import Any
 
 import numpy as np
 import pytest
@@ -93,7 +93,7 @@ def get_output_type(calculation_type: str, sym: bool) -> str:
     return "asym_output"
 
 
-def get_test_case_paths(calculation_type: str, test_cases: Optional[list[str]] = None) -> dict[str, Path]:
+def get_test_case_paths(calculation_type: str, test_cases: list[str] | None = None) -> dict[str, Path]:
     """get a list of all cases, directories in validation datasets"""
     calculation_type_dir = DATA_PATH / calculation_type
     test_case_paths = {
@@ -173,7 +173,7 @@ def _add_cases(case_dir: Path, calculation_type: str, **kwargs):
             )
 
 
-def pytest_cases(get_batch_cases: bool = False, data_dir: Optional[str] = None, test_cases: Optional[list[str]] = None):
+def pytest_cases(get_batch_cases: bool = False, data_dir: str | None = None, test_cases: list[str] | None = None):
     if data_dir is not None:
         relevant_calculations = [data_dir]
     else:
@@ -191,7 +191,7 @@ def pytest_cases(get_batch_cases: bool = False, data_dir: Optional[str] = None,
             )
 
 
-def bool_params(true_id: str, false_id: Optional[str] = None, **kwargs):
+def bool_params(true_id: str, false_id: str | None = None, **kwargs):
     if false_id is None:
         false_id = f"not-{true_id}"
     yield pytest.param(False, **kwargs, id=false_id)