diff --git a/CHANGELOG.md b/CHANGELOG.md
index 591232bfc..833a3f149 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -71,6 +71,7 @@ If upgrading from v2.x, see the [v3.0.0 release notes](https://github.com/flixOp
 ### 📝 Docs
 
 ### 👷 Development
+- Added type hints for submodel in all Interface classes
 
 ### 🚧 Known Issues
 
diff --git a/flixopt/calculation.py b/flixopt/calculation.py
index 9d2164e1e..57f42e761 100644
--- a/flixopt/calculation.py
+++ b/flixopt/calculation.py
@@ -54,6 +54,8 @@ class for defined way of solving a flow_system optimization
         active_timesteps: Deprecated. Use FlowSystem.sel(time=...) or FlowSystem.isel(time=...) instead.
     """
 
+    model: FlowSystemModel | None
+
     def __init__(
         self,
         name: str,
@@ -88,7 +90,7 @@ def __init__(
         flow_system._used_in_calculation = True
 
         self.flow_system = flow_system
-        self.model: FlowSystemModel | None = None
+        self.model = None
 
         self.durations = {'modeling': 0.0, 'solving': 0.0, 'saving': 0.0}
         self.folder = pathlib.Path.cwd() / 'results' if folder is None else pathlib.Path(folder)
diff --git a/flixopt/components.py b/flixopt/components.py
index 09156e1dc..86610c3d2 100644
--- a/flixopt/components.py
+++ b/flixopt/components.py
@@ -160,6 +160,8 @@ class LinearConverter(Component):
 
     """
 
+    submodel: LinearConverterModel | None
+
     def __init__(
         self,
         label: str,
@@ -376,6 +378,8 @@ class Storage(Component):
         With flow rates in m3/h, the charge state is therefore in m3.
     """
 
+    submodel: StorageModel | None
+
     def __init__(
         self,
         label: str,
@@ -640,6 +644,8 @@ class Transmission(Component):
 
     """
 
+    submodel: TransmissionModel | None
+
     def __init__(
         self,
         label: str,
diff --git a/flixopt/effects.py b/flixopt/effects.py
index 6225734fe..f4a20c4dc 100644
--- a/flixopt/effects.py
+++ b/flixopt/effects.py
@@ -159,6 +159,8 @@ class Effect(Element):
 
     """
 
+    submodel: EffectModel | None
+
     def __init__(
         self,
         label: str,
@@ -453,12 +455,14 @@ class EffectCollection:
     Handling all Effects
     """
 
+    submodel: EffectCollectionModel | None
+
     def __init__(self, *effects: Effect):
         self._effects = {}
         self._standard_effect: Effect | None = None
         self._objective_effect: Effect | None = None
 
-        self.submodel: EffectCollectionModel | None = None
+        self.submodel = None
         self.add_effects(*effects)
 
     def create_model(self, model: FlowSystemModel) -> EffectCollectionModel:
diff --git a/flixopt/elements.py b/flixopt/elements.py
index a0fd306c0..d983d4432 100644
--- a/flixopt/elements.py
+++ b/flixopt/elements.py
@@ -178,6 +178,8 @@ class Bus(Element):
         by the FlowSystem during system setup.
     """
 
+    submodel: BusModel | None
+
     def __init__(
         self,
         label: str,
@@ -362,6 +364,8 @@ class Flow(Element):
 
     """
 
+    submodel: FlowModel | None
+
     def __init__(
         self,
         label: str,
diff --git a/flixopt/flow_system.py b/flixopt/flow_system.py
index ad43c183b..f97fb3603 100644
--- a/flixopt/flow_system.py
+++ b/flixopt/flow_system.py
@@ -75,6 +75,8 @@ class FlowSystem(Interface):
         connected_and_transformed automatically when trying to solve a calculation.
     """
 
+    model: FlowSystemModel | None
+
     def __init__(
         self,
         timesteps: pd.DatetimeIndex,
diff --git a/flixopt/results.py b/flixopt/results.py
index 75f8f300e..018619cb0 100644
--- a/flixopt/results.py
+++ b/flixopt/results.py
@@ -115,6 +115,8 @@ class CalculationResults:
 
     """
 
+    model: linopy.Model | None
+
     @classmethod
     def from_file(cls, folder: str | pathlib.Path, name: str) -> CalculationResults:
         """Load CalculationResults from saved files.
diff --git a/flixopt/structure.py b/flixopt/structure.py
index 07c558eee..8e89feca4 100644
--- a/flixopt/structure.py
+++ b/flixopt/structure.py
@@ -856,6 +856,8 @@ def __deepcopy__(self, memo):
 class Element(Interface):
     """This class is the basic Element of flixopt. Every Element has a label"""
 
+    submodel: ElementModel | None
+
     def __init__(self, label: str, meta_data: dict | None = None):
         """
         Args:
@@ -864,7 +866,7 @@ def __init__(self, label: str, meta_data: dict | None = None):
         """
         self.label = Element._valid_label(label)
         self.meta_data = meta_data if meta_data is not None else {}
-        self.submodel: ElementModel | None = None
+        self.submodel = None
 
     def _plausibility_checks(self) -> None:
         """This function is used to do some basic plausibility checks for each Element during initialization.