Make Linker.backend a classmethod

cuda_core/cuda/core/_linker.pyx

@@ -167,10 +167,22 @@ cdef class Linker:
         else:
             return as_py(self._culink_handle)
 
-    @property
-    def backend(self) -> str:
-        """Return this Linker instance's underlying backend."""
-        return "nvJitLink" if self._use_nvjitlink else "driver"
+    @classmethod
+    def backend(cls) -> str:
+        """Return which linking backend will be used.
+
+        Returns ``"nvJitLink"`` when the nvJitLink library is available
+        and meets the minimum version requirement, otherwise ``"driver"``.
+
+        .. note::
+
+            Prefer letting :class:`Linker` decide. Query ``backend()``
+            only when you need to dispatch based on input format (for
+            example: choose PTX vs. LTOIR before constructing a
+            ``Linker``). The returned string names an implementation
+            detail whose support matrix may shift across CTK releases.
+        """
+        return "driver" if _decide_nvjitlink_or_driver() else "nvJitLink"
 
 
 # =============================================================================

cuda_core/cuda/core/_program.pyx

@@ -649,7 +649,7 @@ cdef inline int Program_init(Program self, object code, str code_type, object op
         self._linker = Linker(
             ObjectCode._init(code.encode(), code_type), options=_translate_program_options(options)
         )
-        self._backend = self._linker.backend
+        self._backend = self._linker.backend()
 
     elif code_type == "nvvm":
         _get_nvvm_module()  # Validate NVVM availability

cuda_core/docs/source/release/1.0.0-notes.rst

@@ -13,12 +13,6 @@ Highlights
 - TBD
 
 
-New features
-------------
-
-- TBD
-
-
 Breaking changes
 ----------------
 
@@ -113,6 +107,18 @@ Breaking changes
     ``CUgraphConditionalHandle`` value. Previously, ``.handle`` had to be
     extracted explicitly.
 
+- :meth:`Linker.backend` is now a classmethod instead of an instance property.
+  Call sites must use ``Linker.backend()`` (with parentheses) instead of
+  ``linker.backend``. This allows querying the linking backend without
+  constructing a ``Linker`` instance — for example, to choose between PTX and
+  LTOIR input before linking.
+
+
+New features
+------------
+
+- TBD
+
 
 Fixes and enhancements
 -----------------------

cuda_core/tests/test_linker.py

@@ -2,6 +2,8 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
+import inspect
+
 import pytest
 
 from cuda.core import Device, Linker, LinkerOptions, Program, ProgramOptions, _linker
@@ -92,7 +94,7 @@ def test_linker_init(compile_ptx_functions, options):
     linker = Linker(*compile_ptx_functions, options=options)
     object_code = linker.link("cubin")
     assert isinstance(object_code, ObjectCode)
-    assert linker.backend == ("driver" if is_culink_backend else "nvJitLink")
+    assert linker.backend() == ("driver" if is_culink_backend else "nvJitLink")
 
 
 def test_linker_init_invalid_arch(compile_ptx_functions):
@@ -242,3 +244,40 @@ def test_linker_options_nvjitlink_options_as_str():
     assert f"-arch={ARCH}" in options
     assert "-g" in options
     assert "-lineinfo" in options
+
+
+class TestBackendClassmethod:
+    def test_backend_returns_nvjitlink(self, monkeypatch):
+        monkeypatch.setattr(_linker, "_use_nvjitlink_backend", True)
+        assert Linker.backend() == "nvJitLink"
+
+    def test_backend_returns_driver(self, monkeypatch):
+        monkeypatch.setattr(_linker, "_use_nvjitlink_backend", False)
+        assert Linker.backend() == "driver"
+
+    def test_backend_invokes_probe_when_not_memoised(self, monkeypatch):
+        monkeypatch.setattr(_linker, "_use_nvjitlink_backend", None)
+        called = []
+
+        def fake_decide():
+            called.append(True)
+            return False  # False = not falling back to driver = nvJitLink
+
+        monkeypatch.setattr(_linker, "_decide_nvjitlink_or_driver", fake_decide)
+        result = Linker.backend()
+        assert result == "nvJitLink"
+        assert called, "_decide_nvjitlink_or_driver was not called"
+
+    def test_backend_is_classmethod(self):
+        attr = inspect.getattr_static(Linker, "backend")
+        assert isinstance(attr, classmethod)
+
+    def test_backend_is_not_property(self):
+        """backend is a classmethod, not a property.
+
+        This is an intentional breaking change from the prior property API.
+        Attribute-style access (``linker.backend``) now returns a bound method,
+        not a string. All call sites must use parens: ``Linker.backend()``.
+        """
+        attr = inspect.getattr_static(Linker, "backend")
+        assert not isinstance(attr, property)