diff --git a/finetune.py b/finetune.py
index b1b7a12..71b4cdf 100644
--- a/finetune.py
+++ b/finetune.py
@@ -514,6 +514,18 @@ def run(args):
         )
         logging.info("=" * 60)
 
+    # Enable/disable stress based on stress_loss_weight
+    # None = not specified, keep model default; 0 = explicitly disable; >0 = explicitly enable
+    if args.stress_loss_weight is not None:
+        if args.stress_loss_weight > 0:
+            model.enable_stress()
+            logging.info(
+                "Stress training ENABLED (stress_loss_weight=%.4f)", args.stress_loss_weight
+            )
+        elif model.has_stress:
+            model.disable_stress()
+            logging.info("Stress training DISABLED (stress_loss_weight=0.0)")
+
     model_params = sum(p.numel() for p in model.parameters() if p.requires_grad)
     logging.info(f"Model has {model_params:,} trainable parameters.")
 
diff --git a/orb_models/forcefield/models/conservative_regressor.py b/orb_models/forcefield/models/conservative_regressor.py
index 115995f..834e5a6 100644
--- a/orb_models/forcefield/models/conservative_regressor.py
+++ b/orb_models/forcefield/models/conservative_regressor.py
@@ -94,21 +94,11 @@ def __init__(
         self.forces_target = PROPERTIES[self.forces_name]
         self.grad_forces_name = f"{self.grad_prefix}_{self.forces_name}"
 
-        # Stress is optional since only periodic systems have it
+        # Stress names are always derived (from level_of_theory); has_stress toggles computation
+        self.stress_name: str = f"stress-{level_of_theory}" if level_of_theory else "stress"
+        self.stress_target: PropertyDefinition = PROPERTIES[self.stress_name]
+        self.grad_stress_name: str = f"{self.grad_prefix}_{self.stress_name}"
         self.has_stress = has_stress
-        if self.has_stress:
-            self.stress_name: str | None = (
-                f"stress-{level_of_theory}" if level_of_theory else "stress"
-            )
-            self.stress_target: PropertyDefinition | None = PROPERTIES[self.stress_name]
-            self.grad_stress_name: str | None = f"{self.grad_prefix}_{self.stress_name}"
-        else:
-            self.stress_name = None
-            self.stress_target = None
-            self.grad_stress_name = None
-        assert self.has_stress == (self.grad_stress_name is not None), (
-            "grad_stress_name must be set if has_stress is True"
-        )
 
         self.grad_rotation_name = "rotational_grad"
 
@@ -117,6 +107,14 @@ def __init__(
             if heads[name] is not None:
                 self.extra_properties.append(heads[name].target.fullname)
 
+    def enable_stress(self) -> None:
+        """Enable stress computation."""
+        self.has_stress = True
+
+    def disable_stress(self) -> None:
+        """Disable stress computation."""
+        self.has_stress = False
+
     @property
     def properties(self):
         """List of names of predicted properties."""
@@ -126,9 +124,12 @@ def properties(self):
             self.grad_forces_name,
             self.grad_rotation_name,
         ]
-        if self.grad_stress_name is not None:
+        if self.has_stress:
             props.append(self.grad_stress_name)
-        props.extend(self.extra_properties)
+        for name in self.extra_properties:
+            if not self.has_stress and "stress" in name:
+                continue
+            props.append(name)
         return props
 
     def forward(self, batch: AtomGraphs) -> dict[str, torch.Tensor]:
@@ -179,7 +180,7 @@ def predict(self, batch: AtomGraphs, split: bool = False) -> dict[str, torch.Ten
         energy_head = cast(ForcefieldHead, self.heads[self.energy_name])
         out[self.energy_name] = energy_head.denormalize(preds[self.energy_name], batch)
         out[self.grad_forces_name] = preds[self.grad_forces_name]
-        if self.grad_stress_name:
+        if self.has_stress:
             out[self.grad_stress_name] = preds[self.grad_stress_name]
         out[self.grad_rotation_name] = preds[self.grad_rotation_name]
         for name in self.extra_properties:
@@ -242,8 +243,6 @@ def loss(self, batch: AtomGraphs) -> base.ModelOutput:
 
         # Conservative stress (optional)
         if self.has_stress and self.grad_stress_name in out:
-            assert self.stress_name is not None
-            assert self.grad_stress_name is not None
             raw_grad_stress_pred = out[self.grad_stress_name]
             grad_stress_pred = self.grad_stress_normalizer(raw_grad_stress_pred, online=False)
             loss_out = stress_loss_function(
@@ -267,7 +266,6 @@ def loss(self, batch: AtomGraphs) -> base.ModelOutput:
             if self.has_stress and self.grad_stress_name in out
             else []
         ):
-            assert grad_name is not None
             direct_name = grad_name.replace(self.grad_prefix + "_", "")
             if direct_name in self.extra_properties:
                 direct_head = cast(ForcefieldHead, self.heads[direct_name])
diff --git a/orb_models/forcefield/models/direct_regressor.py b/orb_models/forcefield/models/direct_regressor.py
index 681c1b5..4d4e727 100644
--- a/orb_models/forcefield/models/direct_regressor.py
+++ b/orb_models/forcefield/models/direct_regressor.py
@@ -57,6 +57,7 @@ def __init__(
         _validate_heads_and_loss_weights(heads, loss_weights)
 
         self.heads = torch.nn.ModuleDict(heads)
+        self._stress_disabled = False
         self.loss_weights = loss_weights
         self.model_requires_grad = model_requires_grad
         self.cutoff_layers = cutoff_layers
@@ -82,20 +83,34 @@ def __init__(
 
     @property
     def has_stress(self) -> bool:
-        """Check if the model has stress prediction."""
-        return "stress" in self.heads
+        """Check if the model has stress prediction and it is enabled."""
+        return "stress" in self.heads and not self._stress_disabled
+
+    def enable_stress(self) -> None:
+        """Enable stress computation."""
+        if "stress" not in self.heads:
+            raise ValueError("Cannot enable stress: no stress head exists.")
+        self._stress_disabled = False
+
+    def disable_stress(self) -> None:
+        """Disable stress computation."""
+        self._stress_disabled = True
 
     def forward(self, batch: AtomGraphs) -> dict[str, torch.Tensor | dict[str, torch.Tensor]]:
         """Forward pass of DirectForcefieldRegressor."""
         out = self.model(batch)
         node_features = out["node_features"]
         for name, head in self.heads.items():
+            if self._stress_disabled and "stress" in name:
+                continue
             res = head(node_features, batch)
             out[name] = res
 
         if self.pair_repulsion:
             out_pair_repulsion = self.pair_repulsion_fn(batch)
             for name, head in self.heads.items():
+                if self._stress_disabled and "stress" in name:
+                    continue
                 raw_repulsion = self._get_raw_repulsion(name, out_pair_repulsion)
                 if raw_repulsion is not None:
                     head = cast(ForcefieldHead, head)
@@ -109,11 +124,15 @@ def predict(self, batch: AtomGraphs, split: bool = False) -> dict[str, torch.Ten
         node_features = out["node_features"]
         output = {}
         for name, head in self.heads.items():
+            if self._stress_disabled and "stress" in name:
+                continue
             output[name] = cast(ForcefieldHead | ConfidenceHead, head).predict(node_features, batch)
 
         if self.pair_repulsion:
             out_pair_repulsion = self.pair_repulsion_fn(batch)
             for name, head in self.heads.items():
+                if self._stress_disabled and "stress" in name:
+                    continue
                 raw_repulsion = self._get_raw_repulsion(name, out_pair_repulsion)
                 if raw_repulsion is not None:
                     output[name] = output[name] + raw_repulsion
@@ -138,6 +157,8 @@ def loss(self, batch: AtomGraphs) -> base.ModelOutput:
         for name, head in self.heads.items():
             if name == "confidence":
                 continue
+            if self._stress_disabled and "stress" in name:
+                continue
             head = cast(ForcefieldHead, head)
             head_out = head.loss(out[name], batch)
             weight = self.loss_weights[name]
@@ -191,6 +212,8 @@ def load_state_dict(
     def properties(self):
         """List of names of predicted properties."""
         heads = list(self.heads.keys())
+        if self._stress_disabled:
+            heads = [head for head in heads if "stress" not in head]
         if "energy" in heads:
             heads.append("free_energy")
         return heads
diff --git a/pyproject.toml b/pyproject.toml
index 94f6d60..1ea19e8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -20,7 +20,7 @@ dependencies = [
     "torch>=2.8.0, <3.0.0",
     "dm-tree==0.1.8", # Pinned because of https://github.com/google-deepmind/tree/issues/128
     "tqdm>=4.67.1",
-    "nvalchemi-toolkit-ops>=0.2.0",
+    "nvalchemi-toolkit-ops>=0.2.0,<0.3.0",
 ]
 
 [project.optional-dependencies]
diff --git a/tests/forcefield/test_calculator.py b/tests/forcefield/test_calculator.py
index b1f0035..e69baa3 100644
--- a/tests/forcefield/test_calculator.py
+++ b/tests/forcefield/test_calculator.py
@@ -52,3 +52,57 @@ def test_calc_non_conservative_defaults(direct_regressor):
         "forces",
         "stress",
     }
+
+
+class TestStressToggle:
+    """Test that enable_stress/disable_stress controls stress in calculator results."""
+
+    def test_conservative_stress_disabled(self, conservative_regressor, mptraj_10_systems_db):
+        conservative_regressor.disable_stress()
+        calc = ORBCalculator(
+            model=conservative_regressor,
+            atoms_adapter=ForcefieldAtomsAdapter(6.0, 20),
+        )
+        assert "stress" not in calc.implemented_properties
+        atoms = mptraj_10_systems_db.get_atoms(1)
+        calc.calculate(atoms)
+        assert "stress" not in calc.results
+        assert "forces" in calc.results
+
+    def test_conservative_stress_enabled(self, conservative_regressor, mptraj_10_systems_db):
+        conservative_regressor.disable_stress()
+        conservative_regressor.enable_stress()
+        calc = ORBCalculator(
+            model=conservative_regressor,
+            atoms_adapter=ForcefieldAtomsAdapter(6.0, 20),
+        )
+        assert "stress" in calc.implemented_properties
+        atoms = mptraj_10_systems_db.get_atoms(1)
+        calc.calculate(atoms)
+        assert "stress" in calc.results
+        assert "forces" in calc.results
+
+    def test_direct_stress_disabled(self, direct_regressor, mptraj_10_systems_db):
+        direct_regressor.disable_stress()
+        calc = ORBCalculator(
+            model=direct_regressor,
+            atoms_adapter=ForcefieldAtomsAdapter(6.0, 20),
+        )
+        assert "stress" not in calc.implemented_properties
+        atoms = mptraj_10_systems_db.get_atoms(1)
+        calc.calculate(atoms)
+        assert "stress" not in calc.results
+        assert "forces" in calc.results
+
+    def test_direct_stress_enabled(self, direct_regressor, mptraj_10_systems_db):
+        direct_regressor.disable_stress()
+        direct_regressor.enable_stress()
+        calc = ORBCalculator(
+            model=direct_regressor,
+            atoms_adapter=ForcefieldAtomsAdapter(6.0, 20),
+        )
+        assert "stress" in calc.implemented_properties
+        atoms = mptraj_10_systems_db.get_atoms(1)
+        calc.calculate(atoms)
+        assert "stress" in calc.results
+        assert "forces" in calc.results
diff --git a/tests/forcefield/test_orb_torchsim.py b/tests/forcefield/test_orb_torchsim.py
index 3486230..ac37c7d 100644
--- a/tests/forcefield/test_orb_torchsim.py
+++ b/tests/forcefield/test_orb_torchsim.py
@@ -70,3 +70,49 @@ def test_orb_torchsim_interface(edge_method, conservative_regressor, mptraj_10_s
             atol=1e-5,
             equal_nan=True,
         )
+
+
+class TestOrbTorchSimStressToggle:
+    """Test that enable_stress/disable_stress controls stress in OrbTorchSimModel results."""
+
+    def test_conservative_stress_disabled(self, conservative_regressor, mptraj_10_systems_db):
+        conservative_regressor.disable_stress()
+        atoms_list = [mptraj_10_systems_db.get_atoms(1)]
+        adapter = ForcefieldAtomsAdapter(6.0, 120)
+        sim_state = ts.io.atoms_to_state(atoms_list, "cpu", torch.get_default_dtype())
+        sim_model = OrbTorchSimModel(conservative_regressor, adapter)
+        results = sim_model(sim_state)
+        assert "stress" not in results
+        assert "forces" in results
+
+    def test_conservative_stress_enabled(self, conservative_regressor, mptraj_10_systems_db):
+        conservative_regressor.disable_stress()
+        conservative_regressor.enable_stress()
+        atoms_list = [mptraj_10_systems_db.get_atoms(1)]
+        adapter = ForcefieldAtomsAdapter(6.0, 120)
+        sim_state = ts.io.atoms_to_state(atoms_list, "cpu", torch.get_default_dtype())
+        sim_model = OrbTorchSimModel(conservative_regressor, adapter)
+        results = sim_model(sim_state)
+        assert "stress" in results
+        assert "forces" in results
+
+    def test_direct_stress_disabled(self, direct_regressor, mptraj_10_systems_db):
+        direct_regressor.disable_stress()
+        atoms_list = [mptraj_10_systems_db.get_atoms(1)]
+        adapter = ForcefieldAtomsAdapter(6.0, 120)
+        sim_state = ts.io.atoms_to_state(atoms_list, "cpu", torch.get_default_dtype())
+        sim_model = OrbTorchSimModel(direct_regressor, adapter)
+        results = sim_model(sim_state)
+        assert "stress" not in results
+        assert "forces" in results
+
+    def test_direct_stress_enabled(self, direct_regressor, mptraj_10_systems_db):
+        direct_regressor.disable_stress()
+        direct_regressor.enable_stress()
+        atoms_list = [mptraj_10_systems_db.get_atoms(1)]
+        adapter = ForcefieldAtomsAdapter(6.0, 120)
+        sim_state = ts.io.atoms_to_state(atoms_list, "cpu", torch.get_default_dtype())
+        sim_model = OrbTorchSimModel(direct_regressor, adapter)
+        results = sim_model(sim_state)
+        assert "stress" in results
+        assert "forces" in results