diff --git a/examples/ex1a_canti2d.py b/examples/ex1a_canti2d.py
index 645fefc..667af78 100644
--- a/examples/ex1a_canti2d.py
+++ b/examples/ex1a_canti2d.py
@@ -222,7 +222,6 @@ def main() -> None:
     project = build_ex1a_canti2d()
     project.validate_references()
     gm = next(ts for ts in project.time_series if ts.id == 3)
-    assert isinstance(gm, PathTimeSeries)
     print(f"Built '{project.meta.name}'")
     print(f"  Gravity + pushover + earthquake cases: {len(project.analyses)}")
     print(f"  Ground motion file: {GROUND_MOTION_FILE.name}")
diff --git a/examples/ex1a_canti2d_eq.py b/examples/ex1a_canti2d_eq.py
index 4e616d5..f809437 100644
--- a/examples/ex1a_canti2d_eq.py
+++ b/examples/ex1a_canti2d_eq.py
@@ -190,7 +190,6 @@ def main() -> None:
     project = build_ex1a_canti2d_eq()
     project.validate_references()
     gm = next(ts for ts in project.time_series if ts.id == 2)
-    assert isinstance(gm, PathTimeSeries)
     print(f"Built '{project.meta.name}'")
     print(f"  Ground motion file: {GROUND_MOTION_FILE.name}")
     print(f"  Reference Tcl: {REFERENCE_TCL.name}")
diff --git a/examples/ex1b_portal2d.py b/examples/ex1b_portal2d.py
index c8e80e3..12d6589 100644
--- a/examples/ex1b_portal2d.py
+++ b/examples/ex1b_portal2d.py
@@ -209,7 +209,6 @@ def main() -> None:
     project = build_ex1b_portal2d()
     project.validate_references()
     gm = next(ts for ts in project.time_series if ts.id == 3)
-    assert isinstance(gm, PathTimeSeries)
     print(f"Built '{project.meta.name}'")
     print(f"  Gravity + pushover + earthquake cases: {len(project.analyses)}")
     print(f"  Ground motion file: {GROUND_MOTION_FILE.name}")
diff --git a/examples/ex2a_canti2d_elastic_element.py b/examples/ex2a_canti2d_elastic_element.py
index f39f791..24a1708 100644
--- a/examples/ex2a_canti2d_elastic_element.py
+++ b/examples/ex2a_canti2d_elastic_element.py
@@ -231,7 +231,6 @@ def main() -> None:
     project = build_ex2a_canti2d_elastic_element()
     project.validate_references()
     gm = next(ts for ts in project.time_series if ts.id == 3)
-    assert isinstance(gm, PathTimeSeries)
     print(f"Built '{project.meta.name}'")
     print(f"  LCol={L_COL}, Weight={WEIGHT}, ACol={A_COL:.1f}, Ec={E_C:.3f}")
     print(f"  Gravity + pushover + earthquake cases: {len(project.analyses)}")
diff --git a/examples/ex2b_canti2d_inelastic_section.py b/examples/ex2b_canti2d_inelastic_section.py
index d8444b1..0a00eaa 100644
--- a/examples/ex2b_canti2d_inelastic_section.py
+++ b/examples/ex2b_canti2d_inelastic_section.py
@@ -253,7 +253,6 @@ def main() -> None:
     project = build_ex2b_canti2d_inelastic_section()
     project.validate_references()
     gm = next(ts for ts in project.time_series if ts.id == 400)
-    assert isinstance(gm, PathTimeSeries)
     print(f"Built '{project.meta.name}'")
     print(
         f"  LCol={L_COL}, EA={EA_COL:.1f}, My={MY_COL:.1f}, "
diff --git a/examples/ex2c_canti2d_inelastic_fiber_section.py b/examples/ex2c_canti2d_inelastic_fiber_section.py
index 0f64fec..3a3ec53 100644
--- a/examples/ex2c_canti2d_inelastic_fiber_section.py
+++ b/examples/ex2c_canti2d_inelastic_fiber_section.py
@@ -301,7 +301,6 @@ def main() -> None:
     project = build_ex2c_canti2d_inelastic_fiber_section()
     project.validate_references()
     gm = next(ts for ts in project.time_series if ts.id == 400)
-    assert isinstance(gm, PathTimeSeries)
     print(f"Built '{project.meta.name}'")
     print(
         f"  LCol={L_COL}, ACol={A_COL:.1f}, Iz={IZ_COL:.1f}, "
diff --git a/src/otko/services/export.py b/src/otko/services/export.py
index 1ae5710..f3ca54d 100644
--- a/src/otko/services/export.py
+++ b/src/otko/services/export.py
@@ -49,7 +49,7 @@ from otko.services.opensees_runner import OpenSeesRunner
 __all__ = ["RecordingOps", "export_opspy", "export_tcl"]
 
 #: Pinned solver version written into every script header.
-PINNED_OPENSEESPY = "openseespy==3.8.0.0"
+PINNED_OPENSEESPY = "openseespy==3.5.1.12"
 
 #: Recorded call triple: (ops method name, positional args, keyword args).
 RecordedCall = tuple[str, tuple[Any, ...], dict[str, Any]]
@@ -362,7 +362,7 @@ def export_opspy(project: Project, case_id: int | None = None) -> str:
             are appended after the model.
 
     Returns:
-        The script source. The header pins ``openseespy==3.8.0.0``,
+        The script source. The header pins ``openseespy==3.5.1.12``,
         the OTKO version and the display units.
 
     Raises:
diff --git a/tests/unit/test_export.py b/tests/unit/test_export.py
index 98c23ec..ae64063 100644
--- a/tests/unit/test_export.py
+++ b/tests/unit/test_export.py
@@ -109,14 +109,14 @@ def _path_series_project() -> Project:
 class TestHeader:
     def test_opspy_header_pins_solver_version_and_units(self) -> None:
         script = export_opspy(_truss_2d())
-        assert PINNED_OPENSEESPY == "openseespy==3.8.0.0"
-        assert "openseespy==3.8.0.0" in script
+        assert PINNED_OPENSEESPY == "openseespy==3.5.1.12"
+        assert "openseespy==3.5.1.12" in script
         assert __version__ in script
         assert _truss_2d().meta.units.value in script
 
     def test_tcl_header_pins_solver_version_and_units(self) -> None:
         script = export_tcl(_truss_2d())
-        assert "openseespy==3.8.0.0" in script
+        assert "openseespy==3.5.1.12" in script
         assert __version__ in script