diff --git a/cuda_bindings_12/pyproject.toml b/cuda_bindings_12/pyproject.toml
index aee928a8aef..bed6398769f 100644
--- a/cuda_bindings_12/pyproject.toml
+++ b/cuda_bindings_12/pyproject.toml
@@ -104,6 +104,9 @@ ignore = [
 exclude = ["cuda/bindings/_version.py"]
 
 [tool.ruff.lint.per-file-ignores]
+# This config replaces ../ruff.toml for this tree, so it repeats that file's
+# S101 policy: asserts are rejected only in cuda_core/cuda/core.
+"**" = ["S101"]
 "setup.py" = ["F401"]
 "__init__.py" = ["F401"]
 "site-packages/_cuda_bindings_redirector.py" = ["F401"]
diff --git a/cuda_core/cuda/core/_device.pyx b/cuda_core/cuda/core/_device.pyx
index 29b515bbe17..5ce22959e98 100644
--- a/cuda_core/cuda/core/_device.pyx
+++ b/cuda_core/cuda/core/_device.pyx
@@ -1684,7 +1684,11 @@ cdef inline int Device_resolve_device_id(device_id) except? -1:
         elif err == cydriver.CUresult.CUDA_ERROR_INVALID_CONTEXT:
             with nogil:
                 HANDLE_RETURN(cydriver.cuCtxGetCurrent(&ctx))
-            assert <void*>(ctx) == NULL
+            if <void*>(ctx) != NULL:
+                raise RuntimeError(
+                    "internal cuda.core error, please report: cuCtxGetDevice returned "
+                    "CUDA_ERROR_INVALID_CONTEXT while a context is current"
+                )
             return 0  # cudart behavior
         else:
             HANDLE_RETURN(err)
diff --git a/cuda_core/cuda/core/_layout.pyx b/cuda_core/cuda/core/_layout.pyx
index 1935e9969fa..4ebc9234258 100644
--- a/cuda_core/cuda/core/_layout.pyx
+++ b/cuda_core/cuda/core/_layout.pyx
@@ -1182,7 +1182,10 @@ cdef inline int unsqueeze_extents(BaseLayout& out_layout, BaseLayout& in_layout,
             out_layout.shape[i] = in_shape[in_i]
             out_layout.strides[i] = in_strides[in_i]
             in_i += 1
-    assert in_i == ndim
+    if in_i != ndim:
+        raise RuntimeError(
+            f"internal cuda.core error, please report: unsqueeze_extents consumed {in_i} of {ndim} input axes"
+        )
     return 0
 
 
diff --git a/cuda_core/cuda/core/_memory/_managed_buffer.py b/cuda_core/cuda/core/_memory/_managed_buffer.py
index 42acc5f2315..662ef8c118f 100644
--- a/cuda_core/cuda/core/_memory/_managed_buffer.py
+++ b/cuda_core/cuda/core/_memory/_managed_buffer.py
@@ -276,7 +276,8 @@ def accessed_by(self, locations: Iterable[Device | Host]) -> None:
             target.add(loc)
         for loc in target:
             spec = _coerce_location(loc)
-            assert spec is not None
+            if spec is None:
+                raise RuntimeError(f"internal cuda.core error, please report: no location spec for {loc!r}")
             if spec.kind not in ("device", "host"):
                 raise ValueError(f"advise {_SET_ACCESSED_BY.name} does not support location_type='{spec.kind}'")
         current = set(_query_accessed_by(self))
diff --git a/cuda_core/cuda/core/_memory/_managed_memory_resource.pyx b/cuda_core/cuda/core/_memory/_managed_memory_resource.pyx
index f12be4c246c..f50472758b9 100644
--- a/cuda_core/cuda/core/_memory/_managed_memory_resource.pyx
+++ b/cuda_core/cuda/core/_memory/_managed_memory_resource.pyx
@@ -122,7 +122,8 @@ cdef class ManagedMemoryResource(_MemPool):
             (``prefetch``, ``discard``, ``discard_prefetch``).
         """
         MP_check_open(self)
-        assert isinstance(stream, Stream), "Only Stream is supported for managed memory allocations"
+        if not isinstance(stream, Stream):
+            raise TypeError(f"Only Stream is supported for managed memory allocations, got {type(stream).__name__}")
         if self.is_mapped:
             raise TypeError("Cannot allocate from a mapped IPC-enabled memory resource")
         cdef Stream s = Stream_accept(stream)
diff --git a/cuda_core/cuda/core/_memoryview.pyx b/cuda_core/cuda/core/_memoryview.pyx
index 47fd1cbeefc..287a01a70bc 100644
--- a/cuda_core/cuda/core/_memoryview.pyx
+++ b/cuda_core/cuda/core/_memoryview.pyx
@@ -1044,14 +1044,17 @@ cdef StridedMemoryView view_as_dlpack(obj, stream_ptr, view=None):
         stream_ptr = int(stream_ptr)
     dldevice, device_id = obj.__dlpack_device__()
     if dldevice == _kDLCPU:
-        assert device_id == 0
+        if device_id != 0:
+            raise ValueError(f"__dlpack_device__() reported device_id {device_id} for a kDLCPU tensor; expected 0")
         device_id = -1
         if stream_ptr is None:
             raise BufferError("stream=None is ambiguous with view()")
         elif stream_ptr == -1:
             stream_ptr = None
     elif dldevice == _kDLCUDA:
-        assert device_id >= 0
+        if device_id < 0:
+            raise ValueError(
+                f"__dlpack_device__() reported device_id {device_id} for a kDLCUDA tensor; expected 0 or more")
         is_device_accessible = True
         # no need to check other stream values, it's a pass-through
         if stream_ptr is None:
@@ -1094,7 +1097,7 @@ cdef StridedMemoryView view_as_dlpack(obj, stream_ptr, view=None):
         is_readonly = False
         used_name = DLPACK_TENSOR_USED_NAME
     else:
-        assert False
+        raise ValueError(f"__dlpack__() returned {capsule!r}, not an unconsumed DLPack capsule")
 
     cpython.PyCapsule_SetName(capsule, used_name)
 
@@ -1218,7 +1221,9 @@ cpdef StridedMemoryView view_as_cai(obj, stream_ptr, view=None):
         if stream is not None:
             producer_s = <intptr_t>(stream)
             consumer_s = <intptr_t>(stream_ptr)
-            assert producer_s > 0
+            if producer_s <= 0:
+                raise ValueError(
+                    f"__cuda_array_interface__ reported stream {stream}; expected None or a positive stream handle")
             # establish stream order
             if producer_s != consumer_s:
                 with nogil:
diff --git a/cuda_core/cuda/core/_module.pyx b/cuda_core/cuda/core/_module.pyx
index d4de653406f..52a2794cfa4 100644
--- a/cuda_core/cuda/core/_module.pyx
+++ b/cuda_core/cuda/core/_module.pyx
@@ -632,7 +632,8 @@ cdef class ObjectCode:
 
     @classmethod
     def _init(cls, module, code_type, *, name: str = "", symbol_mapping: dict[str, str] | None = None) -> ObjectCode:
-        assert code_type in _supported_code_type, f"{code_type=} is not supported"
+        if code_type not in _supported_code_type:
+            raise ValueError(f"{code_type=} is not supported")
         cdef ObjectCode self = ObjectCode.__new__(ObjectCode)
 
         # _h_library is assigned during _lazy_load_module
diff --git a/cuda_core/cuda/core/_program.pyx b/cuda_core/cuda/core/_program.pyx
index 94f5bf74f72..c749744c690 100644
--- a/cuda_core/cuda/core/_program.pyx
+++ b/cuda_core/cuda/core/_program.pyx
@@ -1359,7 +1359,8 @@ cdef inline object _prepare_nvvm_options_impl(object opts, bint as_bytes):
     options = []
 
     # Options supported by NVVM
-    assert opts.arch is not None
+    if opts.arch is None:
+        raise RuntimeError("internal cuda.core error, please report: ProgramOptions.arch is None")
     arch = opts.arch
     if arch.startswith("sm_"):
         arch = f"compute_{arch[3:]}"
diff --git a/cuda_core/cuda/core/system/_device.pyx b/cuda_core/cuda/core/system/_device.pyx
index 76bfb128503..f06614420ce 100644
--- a/cuda_core/cuda/core/system/_device.pyx
+++ b/cuda_core/cuda/core/system/_device.pyx
@@ -43,9 +43,8 @@ if TYPE_CHECKING:
 cdef object _pstate_to_int(object pstate):
     if pstate == nvml.Pstates.PSTATE_UNKNOWN:
         return None
-    assert (
-        int(pstate) >= 0 and int(pstate) <= 15
-    ), f"Invalid P-state: {pstate}. Must be between 0 and 15 inclusive, or PSTATE_UNKNOWN."
+    if int(pstate) < 0 or int(pstate) > 15:
+        raise ValueError(f"Invalid P-state: {pstate}. Must be between 0 and 15 inclusive, or PSTATE_UNKNOWN.")
     return int(pstate) - int(nvml.Pstates.PSTATE_0)
 
 
diff --git a/cuda_core/cuda/core/system/_field_values.pxi b/cuda_core/cuda/core/system/_field_values.pxi
index 65259da3768..beca31df6b3 100644
--- a/cuda_core/cuda/core/system/_field_values.pxi
+++ b/cuda_core/cuda/core/system/_field_values.pxi
@@ -12,7 +12,8 @@ cdef class FieldValue:
     cdef object _field_value
 
     def __init__(self, field_value: nvml.FieldValue):
-        assert len(field_value) == 1
+        if len(field_value) != 1:
+            raise ValueError(f"FieldValue expects exactly one field value, got {len(field_value)}")
         self._field_value = field_value
 
     @property
diff --git a/cuda_core/cuda/core/system/_system_events.pyx b/cuda_core/cuda/core/system/_system_events.pyx
index ad1e4bb7847..6e57ad28fb5 100644
--- a/cuda_core/cuda/core/system/_system_events.pyx
+++ b/cuda_core/cuda/core/system/_system_events.pyx
@@ -40,7 +40,8 @@ cdef class SystemEvent:
     cdef object _event_data
 
     def __init__(self, event_data not None: nvml.SystemEventData_v1):
-        assert len(event_data) == 1
+        if len(event_data) != 1:
+            raise ValueError(f"SystemEvent expects exactly one event, got {len(event_data)}")
         self._event_data = event_data
 
     @property
diff --git a/cuda_core/cuda/core/utils/_program_cache/_file_stream.py b/cuda_core/cuda/core/utils/_program_cache/_file_stream.py
index 314c7b612bc..8063d7e6c16 100644
--- a/cuda_core/cuda/core/utils/_program_cache/_file_stream.py
+++ b/cuda_core/cuda/core/utils/_program_cache/_file_stream.py
@@ -93,7 +93,8 @@ def _with_sharing_retry(
             last_exc = exc
     if on_exhausted is not None:
         return on_exhausted(last_exc)
-    assert last_exc is not None  # at least one iteration ran and caught a PermissionError
+    if last_exc is None:
+        raise RuntimeError("internal cuda.core error, please report: sharing retry ran no attempts")
     raise last_exc
 
 
diff --git a/cuda_core/cuda/core/utils/_program_cache/_keys.py b/cuda_core/cuda/core/utils/_program_cache/_keys.py
index 2919f48ee34..2cf5b8913c8 100644
--- a/cuda_core/cuda/core/utils/_program_cache/_keys.py
+++ b/cuda_core/cuda/core/utils/_program_cache/_keys.py
@@ -543,7 +543,8 @@ def hash_version_probe(self, update: Callable[[str, bytes], None]) -> None:
         # so the bytes are still in the digest via ``linker_version``.
         use_driver = self._decide_driver()
         if use_driver is None:
-            assert self._cached_decision_exc is not None
+            if self._cached_decision_exc is None:
+                raise RuntimeError("internal cuda.core error, please report: linker probe failed without an exception")
             _hash_probe_failure(update, "linker", self._cached_decision_exc)
             return
         try:
diff --git a/cuda_core/docs/source/release/1.3.0-notes.rst b/cuda_core/docs/source/release/1.3.0-notes.rst
index 90a36fdc4b4..086d020a623 100644
--- a/cuda_core/docs/source/release/1.3.0-notes.rst
+++ b/cuda_core/docs/source/release/1.3.0-notes.rst
@@ -360,6 +360,25 @@ Fixes and enhancements
   physical allocations.
   (`#2694 <https://github.com/NVIDIA/cuda-python/issues/2694>`__)
 
+- Checks that were ``assert`` statements now raise exceptions, so they also
+  run under ``python -O``, which strips asserts from Python and Cython code.
+  :meth:`~utils.StridedMemoryView.from_dlpack` raises ``ValueError`` when
+  ``__dlpack_device__()`` reports a negative device ID for a CUDA tensor or a
+  nonzero one for a CPU tensor, or when ``__dlpack__()`` returns anything
+  other than an unconsumed DLPack capsule.
+  :meth:`~utils.StridedMemoryView.from_cuda_array_interface` raises
+  ``ValueError`` when the producer's ``stream`` is 0 or negative.
+  :meth:`ManagedMemoryResource.allocate` raises ``TypeError`` when ``stream``
+  is not a :class:`Stream`. Unpickling an :class:`ObjectCode` with an unknown
+  code type raises ``ValueError``, as do :class:`~system._device.FieldValue`
+  and :class:`~system._system_events.SystemEvent` when the NVML data does not
+  hold exactly one entry, and :attr:`system.Device.performance_state` when
+  NVML reports a P-state outside 0 to 15. Before, these raised
+  ``AssertionError``, or nothing under ``python -O``. A failed internal check
+  now raises ``RuntimeError`` with a message that starts with "internal
+  cuda.core error, please report".
+  (`#3202 <https://github.com/NVIDIA/cuda-python/issues/3202>`__)
+
 Deprecations
 ------------
 
diff --git a/cuda_core/tests/system/test_system_device.py b/cuda_core/tests/system/test_system_device.py
index bdef726c099..80be43e75c7 100644
--- a/cuda_core/tests/system/test_system_device.py
+++ b/cuda_core/tests/system/test_system_device.py
@@ -478,6 +478,12 @@ def test_field_value_decodes_signed_long_long():
     assert type(value) is int
 
 
+@pytest.mark.agent_authored(model="claude-opus-5-5")
+def test_field_value_rejects_multiple_values():
+    with pytest.raises(ValueError, match="exactly one field value, got 2"):
+        _device.FieldValue(nvml.FieldValue(2))
+
+
 @pytest.mark.skipif(helpers.IS_WSL or helpers.IS_WINDOWS, reason="Device attributes not supported on WSL or Windows")
 def test_get_all_devices_with_cpu_affinity(subtests):
     for i in range(multiprocessing.cpu_count()):
diff --git a/cuda_core/tests/system/test_system_events.py b/cuda_core/tests/system/test_system_events.py
index 19e7e1f9f57..210149d93d8 100644
--- a/cuda_core/tests/system/test_system_events.py
+++ b/cuda_core/tests/system/test_system_events.py
@@ -36,6 +36,12 @@ def test_system_events_wraps_event_data():
     assert event.gpu_id == 0x0000_0200
 
 
+@pytest.mark.agent_authored(model="claude-opus-5-5")
+def test_system_event_rejects_multiple_events():
+    with pytest.raises(ValueError, match="exactly one event, got 2"):
+        SystemEvent(nvml.SystemEventData_v1(2))
+
+
 @pytest.mark.agent_authored(model="claude-opus-4.7")
 @pytest.mark.parametrize(
     ("gpu_id", "expected"),
diff --git a/cuda_core/tests/test_memory.py b/cuda_core/tests/test_memory.py
index 7217fae0c33..6f42bdc00e0 100644
--- a/cuda_core/tests/test_memory.py
+++ b/cuda_core/tests/test_memory.py
@@ -1152,6 +1152,24 @@ def test_managed_memory_resource_buffer_dlpack_device_type(init_cuda):
     assert view.__dlpack_device__() == (int(DLDeviceType.kDLCUDAManaged), 0)
 
 
+@pytest.mark.agent_authored(model="claude-opus-5-5")
+def test_managed_memory_resource_allocate_rejects_graph_builder(init_cuda):
+    device = init_cuda
+    skip_if_managed_memory_unsupported(device)
+    mr = None
+    gb = None
+    try:
+        mr = create_managed_memory_resource_or_skip(ManagedMemoryResourceOptions(preferred_location=device.device_id))
+        gb = device.create_graph_builder()
+        with pytest.raises(TypeError, match="Only Stream is supported .*got GraphBuilder"):
+            mr.allocate(64, stream=gb)
+    finally:
+        if gb is not None:
+            gb.close()
+        if mr is not None:
+            mr.close()
+
+
 @pytest.mark.parametrize("mr_kind", ["device", "pinned"])
 def test_non_managed_resources_report_not_managed(init_cuda, mr_kind):
     """Non-managed memory resources must report is_managed=False."""
diff --git a/cuda_core/tests/test_module.py b/cuda_core/tests/test_module.py
index 5b8c7a4b791..c2a912fcf57 100644
--- a/cuda_core/tests/test_module.py
+++ b/cuda_core/tests/test_module.py
@@ -727,6 +727,12 @@ def test_module_serialization_roundtrip(get_saxpy_kernel_cubin):
     assert objcode.code_type == result.code_type
 
 
+@pytest.mark.agent_authored(model="claude-opus-5-5")
+def test_module_unpickle_rejects_unknown_code_type():
+    with pytest.raises(ValueError, match="code_type='bogus' is not supported"):
+        ObjectCode._reduce_helper(b"", "bogus", "", None)
+
+
 def test_kernel_from_handle(get_saxpy_kernel_cubin):
     """Test Kernel.from_handle() with a valid handle"""
     original_kernel, objcode = get_saxpy_kernel_cubin
diff --git a/cuda_core/tests/test_utils.py b/cuda_core/tests/test_utils.py
index a54e8378cf9..1e961e173ed 100644
--- a/cuda_core/tests/test_utils.py
+++ b/cuda_core/tests/test_utils.py
@@ -1071,6 +1071,16 @@ def test_view_as_cai_device_pointer_and_stream_ordering(init_cuda):
     dev.default_stream.sync()
 
 
+@pytest.mark.agent_authored(model="claude-opus-5-5")
+def test_view_as_cai_rejects_stream_zero(init_cuda):
+    """The CUDA Array Interface does not allow ``stream`` 0."""
+    consumer = init_cuda.create_stream()
+    obj = _make_cuda_array_interface_obj(shape=(4,), strides=None, typestr="<f4", data=(0, False), stream=0)
+
+    with pytest.raises(ValueError, match="reported stream 0"):
+        StridedMemoryView.from_cuda_array_interface(obj, stream_ptr=consumer.handle)
+
+
 def test_strided_memory_view_init_cai_path_deprecated(init_cuda):
     """The deprecated ``StridedMemoryView(obj)`` constructor routes a CAI-only
     object through the CAI branch (warn + ``view_as_cai``), not the DLPack one."""
diff --git a/cuda_core/tests/test_utils_dlpack.py b/cuda_core/tests/test_utils_dlpack.py
index 43b135e96ce..4664b2da3f3 100644
--- a/cuda_core/tests/test_utils_dlpack.py
+++ b/cuda_core/tests/test_utils_dlpack.py
@@ -225,6 +225,37 @@ def __dlpack__(self, **kwargs):
         StridedMemoryView.from_dlpack(_FakeCudaDevice(), stream_ptr=None)
 
 
+@pytest.mark.agent_authored(model="claude-opus-5-5")
+@pytest.mark.parametrize(("device_type", "device_id"), [(DLDeviceType.kDLCPU, 1), (DLDeviceType.kDLCUDA, -1)])
+def test_from_dlpack_rejects_invalid_device_id(device_type, device_id):
+    """A device ordinal the DLPack device type cannot have is rejected."""
+
+    class _FakeInvalidDeviceId:
+        def __dlpack_device__(self):
+            return (int(device_type), device_id)
+
+        def __dlpack__(self, **kwargs):
+            raise AssertionError("__dlpack__ must not be reached")
+
+    with pytest.raises(ValueError, match=f"reported device_id {device_id}"):
+        StridedMemoryView.from_dlpack(_FakeInvalidDeviceId(), stream_ptr=-1)
+
+
+@pytest.mark.agent_authored(model="claude-opus-5-5")
+def test_from_dlpack_rejects_non_capsule():
+    """``__dlpack__`` must return an unconsumed DLPack capsule."""
+
+    class _FakeNonCapsule:
+        def __dlpack_device__(self):
+            return (int(DLDeviceType.kDLCPU), 0)
+
+        def __dlpack__(self, **kwargs):
+            return object()
+
+    with pytest.raises(ValueError, match="not an unconsumed DLPack capsule"):
+        StridedMemoryView.from_dlpack(_FakeNonCapsule(), stream_ptr=-1)
+
+
 class _DLPackNoMaxVersion:
     """Wraps a StridedMemoryView but rejects the ``max_version`` kwarg, forcing the
     TypeError fallback in ``view_as_dlpack`` and an *unversioned* capsule import.
diff --git a/ruff.toml b/ruff.toml
index 5a2778cfb80..4dcc72d6eb5 100644
--- a/ruff.toml
+++ b/ruff.toml
@@ -58,7 +58,6 @@ ignore = [
   "UP035",  # deprecated-import from typing
 
   # security rules too strict for this project
-  "S101",   # asserts
   "S311",   # allow random.* (not cryptographic)
   "S404",   # allow subprocess imports
 
@@ -81,6 +80,8 @@ known-first-party = ["cuda", "_build_shared"]
 inline-quotes = "double"
 
 [lint.per-file-ignores]
+# cuda.core library code raises explicit errors; `python -O` strips asserts.
+"!cuda_core/cuda/core/**" = ["S101"]
 "__init__.py" = ["F401", "E402", "F403", "F405"]
 "setup.py" = ["F401"]