diff --git a/tests/test_web/test_webapi_mode.py b/tests/test_web/test_webapi_mode.py
index 36355caa9..3cff5621a 100644
--- a/tests/test_web/test_webapi_mode.py
+++ b/tests/test_web/test_webapi_mode.py
@@ -108,11 +108,22 @@ def mock_upload(monkeypatch, set_api_key):
         status=200,
     )
 
+    # store the uploaded stub for verification
+    uploaded_stub = {}
+
+    def mock_upload_simulation(self, stub, **kwargs):
+        uploaded_stub["stub"] = stub
+
     def mock_upload_file(*args, **kwargs):
         pass
 
+    monkeypatch.setattr(
+        "tidy3d.web.core.task_core.SimulationTask.upload_simulation", mock_upload_simulation
+    )
     monkeypatch.setattr("tidy3d.web.core.task_core.upload_file", mock_upload_file)
 
+    return uploaded_stub
+
 
 @pytest.fixture
 def mock_get_info(monkeypatch, set_api_key):
@@ -269,6 +280,26 @@ def test_upload(monkeypatch, mock_upload, mock_get_info, mock_metadata):
     assert upload(sim, TASK_NAME, PROJECT_NAME, reduce_simulation=True)
 
 
+@pytest.mark.parametrize("reduce_simulation", [True, False])
+@responses.activate
+def test_upload_with_reduction_parameter(
+    monkeypatch, mock_upload, mock_get_info, mock_metadata, reduce_simulation
+):
+    """Test that simulation reduction is properly applied before upload based on reduce_simulation parameter."""
+    sim = make_mode_sim()
+
+    upload(sim, TASK_NAME, PROJECT_NAME, reduce_simulation=reduce_simulation)
+
+    if reduce_simulation:
+        expected_sim = get_reduced_simulation(sim, reduce_simulation=True)
+        assert sim != expected_sim
+    else:
+        expected_sim = sim
+
+    uploaded_sim = mock_upload["stub"].simulation
+    assert uploaded_sim == expected_sim
+
+
 @responses.activate
 def test_get_info(mock_get_info):
     assert get_info(TASK_ID).taskId == TASK_ID
diff --git a/tests/test_web/test_webapi_mode_sim.py b/tests/test_web/test_webapi_mode_sim.py
index 413b2b33f..76a823ce2 100644
--- a/tests/test_web/test_webapi_mode_sim.py
+++ b/tests/test_web/test_webapi_mode_sim.py
@@ -104,11 +104,22 @@ def mock_upload(monkeypatch, set_api_key):
         status=200,
     )
 
+    # store the uploaded stub for verification
+    uploaded_stub = {}
+
+    def mock_upload_simulation(self, stub, **kwargs):
+        uploaded_stub["stub"] = stub
+
     def mock_upload_file(*args, **kwargs):
         pass
 
+    monkeypatch.setattr(
+        "tidy3d.web.core.task_core.SimulationTask.upload_simulation", mock_upload_simulation
+    )
     monkeypatch.setattr("tidy3d.web.core.task_core.upload_file", mock_upload_file)
 
+    return uploaded_stub
+
 
 @pytest.fixture
 def mock_get_info(monkeypatch, set_api_key):
@@ -265,6 +276,26 @@ def test_upload(monkeypatch, mock_upload, mock_get_info, mock_metadata):
     assert upload(sim, TASK_NAME, PROJECT_NAME, reduce_simulation=True)
 
 
+@pytest.mark.parametrize("reduce_simulation", [True, False])
+@responses.activate
+def test_upload_with_reduction_parameter(
+    monkeypatch, mock_upload, mock_get_info, mock_metadata, reduce_simulation
+):
+    """Test that simulation reduction is properly applied before upload based on reduce_simulation parameter."""
+    sim = make_mode_sim()
+
+    upload(sim, TASK_NAME, PROJECT_NAME, reduce_simulation=reduce_simulation)
+
+    if reduce_simulation:
+        expected_sim = get_reduced_simulation(sim, reduce_simulation=True)
+        assert sim != expected_sim
+    else:
+        expected_sim = sim
+
+    uploaded_sim = mock_upload["stub"].simulation
+    assert uploaded_sim == expected_sim
+
+
 @responses.activate
 def test_get_info(mock_get_info):
     assert get_info(TASK_ID).taskId == TASK_ID
diff --git a/tidy3d/web/api/webapi.py b/tidy3d/web/api/webapi.py
index 7b720e21f..19c792708 100644
--- a/tidy3d/web/api/webapi.py
+++ b/tidy3d/web/api/webapi.py
@@ -250,6 +250,9 @@ def upload(
 
     """
 
+    if isinstance(simulation, (ModeSolver, ModeSimulation)):
+        simulation = get_reduced_simulation(simulation, reduce_simulation)
+
     stub = Tidy3dStub(simulation=simulation)
     stub.validate_pre_upload(source_required=source_required)
     log.debug("Creating task.")
@@ -279,8 +282,6 @@ def upload(
     remote_sim_file = SIM_FILE_HDF5_GZ
     if task_type == "MODE_SOLVER":
         remote_sim_file = MODE_FILE_HDF5_GZ
-    if task_type == "MODE_SOLVER" or task_type == "MODE":
-        simulation = get_reduced_simulation(simulation, reduce_simulation)
 
     task.upload_simulation(
         stub=stub,
@@ -322,7 +323,6 @@ def get_reduced_simulation(simulation, reduce_simulation):
     there. Note that if we do the latter we may want to also modify the warning below to only
     happen if there are custom media *and* they extend beyond the simulation domain.
     """
-
     if reduce_simulation == "auto":
         if isinstance(simulation, ModeSimulation):
             sim_mediums = simulation.scene.mediums
@@ -339,7 +339,6 @@ def get_reduced_simulation(simulation, reduce_simulation):
                 " Setting 'reduce_simulation=True' will force simulation reduction in all cases and"
                 " silence this warning."
             )
-
     if reduce_simulation:
         return simulation.reduced_simulation_copy
     return simulation