diff --git a/python/snewpy/_model_downloader.py b/python/snewpy/_model_downloader.py
index bb7096f3..c2de85a0 100644
--- a/python/snewpy/_model_downloader.py
+++ b/python/snewpy/_model_downloader.py
@@ -15,7 +15,6 @@
 from importlib.resources import open_text
 from pathlib import Path
 from tqdm.auto import tqdm
-from typing import Optional
 
 from snewpy import model_path
 from snewpy import __version__ as snewpy_version
@@ -79,7 +78,7 @@ class FileHandle:
 
     path: Path
     remote: str = None
-    md5: Optional[str] = None
+    md5: str | None = None
 
     def check(self) -> None:
         """Check if the given file exists locally and has a correct md5 sum.
diff --git a/python/snewpy/flux.py b/python/snewpy/flux.py
index 00baec6a..3cdfa918 100644
--- a/python/snewpy/flux.py
+++ b/python/snewpy/flux.py
@@ -51,7 +51,6 @@
 .. autoclass:: Axes
 
 """
-from typing import Union, Optional
 #from snewpy.neutrino import Flavor
 from snewpy.flavor import FlavorScheme, FlavorMatrix
 from astropy import units as u
@@ -73,8 +72,8 @@ class Axes(IntEnum):
     energy=2, #Energy dimension
     
     @classmethod
-    def get(cls, value:Union['Axes',int,str])->'Axes':
-        "convert string,int or Axes value to Axes"
+    def get(cls, value: 'Axes' | int | str)->'Axes':
+        "convert string, int or Axes value to Axes"
         if isinstance(value,str):
             return cls[value]
         else:
@@ -85,14 +84,14 @@ class _ContainerBase:
     :noindex:
     """
     unit = None
-    def __init__(self, 
+    def __init__(self,
                  data: u.Quantity,
                  flavor: list[FlavorScheme],
-                 time: u.Quantity[u.s], 
+                 time: u.Quantity[u.s],
                  energy: u.Quantity[u.MeV],
                  *,
-                 integrable_axes: Optional[set[Axes]] = None,
-                 flavor_scheme:Optional[FlavorScheme] = None
+                 integrable_axes: set[Axes] | None = None,
+                 flavor_scheme: FlavorScheme | None = None
     ):
         """A container class storing the physical quantity (flux, fluence, rate...), which depends on flavor, time and energy.
 
@@ -204,7 +203,7 @@ def __repr__(self) -> str:
         ]
         return f"{self.__class__.__name__} {self.array.shape} [{self.array.unit}]: <{' x '.join(s)}>"
     
-    def sum(self, axis: Union[Axes,str])->'Container':
+    def sum(self, axis: Axes | str)->'Container':
         """Sum along given axis, producing a Container with the summary quantity.
         
         Parameters
@@ -249,7 +248,7 @@ def sum(self, axis: Union[Axes,str])->'Container':
         axes[axis] = axes[axis].take([0,-1])
         return Container(array,*axes, integrable_axes = self._integrable_axes.difference({axis}))
 
-    def integrate(self, axis:Union[Axes,str], limits:np.ndarray=None)->'Container':
+    def integrate(self, axis: Axes | str, limits:np.ndarray=None)->'Container':
         """Integrate along given axis, producing a Container with the integral quantity.
         
         Parameters
@@ -317,7 +316,7 @@ def integrate(self, axis:Union[Axes,str], limits:np.ndarray=None)->'Container':
         #choose the proper class
         return Container(array, *axes, integrable_axes=self._integrable_axes.difference({axis}))
 
-    def integrate_or_sum(self, axis:Union[Axes,str])->'Container':
+    def integrate_or_sum(self, axis: Axes | str)->'Container':
         if self.can_integrate(axis):
             return self.integrate(axis)
         else:
diff --git a/python/snewpy/neutrino.py b/python/snewpy/neutrino.py
index e5a83bb1..6456fc75 100644
--- a/python/snewpy/neutrino.py
+++ b/python/snewpy/neutrino.py
@@ -4,7 +4,6 @@
 from enum import IntEnum
 from astropy import units as u
 from dataclasses import dataclass
-from typing import Optional
 import numpy as np
 from collections.abc import Mapping
 from .flavor import ThreeFlavor as Flavor
@@ -41,10 +40,10 @@ class MixingParameters3Flavor(Mapping):
     deltaCP: u.Quantity[u.deg]
     #square mass difference
     dm21_2: u.Quantity[u.eV**2]
-    dm32_2: Optional[u.Quantity] = None
-    dm31_2: Optional[u.Quantity] = None
+    dm32_2: u.Quantity | None = None
+    dm31_2: u.Quantity | None = None
     #mass ordering
-    mass_order: Optional[MassHierarchy] = None
+    mass_order: MassHierarchy | None = None
     # Note: in IH, the mass splittings are: m3..............m1..m2.
 
     def __iter__(self):
@@ -124,8 +123,8 @@ class MixingParameters4Flavor(MixingParameters3Flavor):
     theta34: u.Quantity[u.deg] = 0<<u.deg
     #sterile neutrino mass squared differences
     dm41_2: u.Quantity[u.eV**2] = 0<<u.eV**2
-    dm42_2: Optional[u.Quantity] = None
-    dm43_2: Optional[u.Quantity] = None
+    dm42_2: u.Quantity | None = None
+    dm43_2: u.Quantity | None = None
     
     def __post_init__(self):
         super().__post_init__()