diff --git a/src/pyrecest/backend_support/_torch_dtype_promotion_contract.py b/src/pyrecest/backend_support/_torch_dtype_promotion_contract.py
index 3cb184d28..909db39e5 100644
--- a/src/pyrecest/backend_support/_torch_dtype_promotion_contract.py
+++ b/src/pyrecest/backend_support/_torch_dtype_promotion_contract.py
@@ -1,36 +1,65 @@
-"""PyTorch dtype promotion compatibility helpers."""
+"""PyTorch compatibility helpers for NumPy-style backend contracts."""
 
 from __future__ import annotations
 
 
+def _patch_pytorch_concatenate_axis_none_contract(raw_pytorch, torch_module, backend) -> None:
+    """Make PyTorch concatenate flatten inputs when ``axis=None``."""
+    original_concatenate = raw_pytorch.concatenate
+    if getattr(original_concatenate, "_pyrecest_axis_none_contract", False):
+        return
+
+    def concatenate(seq, axis=0, out=None):
+        tensors = [raw_pytorch.array(item) for item in seq]
+        if tensors:
+            tensors = raw_pytorch.convert_to_wider_dtype(tensors)
+        if axis is None:
+            tensors = [torch_module.flatten(tensor) for tensor in tensors]
+            axis = 0
+        result = torch_module.cat(tensors, dim=axis)
+        if out is not None:
+            out.copy_(result)
+            return out
+        return result
+
+    concatenate.__name__ = getattr(original_concatenate, "__name__", "concatenate")
+    concatenate.__doc__ = getattr(original_concatenate, "__doc__", None)
+    concatenate._pyrecest_axis_none_contract = True
+    raw_pytorch.concatenate = concatenate
+    if getattr(backend, "__backend_name__", None) == "pytorch":
+        backend.concatenate = concatenate
+
+
 def patch_pytorch_dtype_promotion_contract() -> None:
-    """Make PyTorch mixed-dtype helpers use Torch's promotion rules."""
+    """Make PyTorch mixed-dtype helpers and concatenate match NumPy-style contracts."""
     try:
+        import pyrecest.backend as backend  # pylint: disable=import-outside-toplevel
         import pyrecest._backend.pytorch as raw_pytorch  # pylint: disable=import-outside-toplevel
         import torch  # pylint: disable=import-outside-toplevel
     except ModuleNotFoundError:  # pragma: no cover - PyTorch backend import failed earlier
         return
 
     original_convert = raw_pytorch.convert_to_wider_dtype
-    if getattr(original_convert, "_pyrecest_torch_promotion_contract", False):
-        return
+    if not getattr(original_convert, "_pyrecest_torch_promotion_contract", False):
+
+        def convert_to_wider_dtype(tensor_list):
+            tensors = list(tensor_list)
+            if not tensors:
+                return tensors
+
+            promoted_dtype = tensors[0].dtype
+            for tensor in tensors[1:]:
+                promoted_dtype = torch.promote_types(promoted_dtype, tensor.dtype)
+
+            if all(tensor.dtype == promoted_dtype for tensor in tensors):
+                return tensors
+            return [raw_pytorch.cast(tensor, dtype=promoted_dtype) for tensor in tensors]
+
+        convert_to_wider_dtype.__name__ = getattr(
+            original_convert, "__name__", "convert_to_wider_dtype"
+        )
+        convert_to_wider_dtype.__doc__ = getattr(original_convert, "__doc__", None)
+        convert_to_wider_dtype._pyrecest_torch_promotion_contract = True
+        raw_pytorch.convert_to_wider_dtype = convert_to_wider_dtype
 
-    def convert_to_wider_dtype(tensor_list):
-        tensors = list(tensor_list)
-        if not tensors:
-            return tensors
-
-        promoted_dtype = tensors[0].dtype
-        for tensor in tensors[1:]:
-            promoted_dtype = torch.promote_types(promoted_dtype, tensor.dtype)
-
-        if all(tensor.dtype == promoted_dtype for tensor in tensors):
-            return tensors
-        return [raw_pytorch.cast(tensor, dtype=promoted_dtype) for tensor in tensors]
-
-    convert_to_wider_dtype.__name__ = getattr(
-        original_convert, "__name__", "convert_to_wider_dtype"
-    )
-    convert_to_wider_dtype.__doc__ = getattr(original_convert, "__doc__", None)
-    convert_to_wider_dtype._pyrecest_torch_promotion_contract = True
-    raw_pytorch.convert_to_wider_dtype = convert_to_wider_dtype
+    _patch_pytorch_concatenate_axis_none_contract(raw_pytorch, torch, backend)
diff --git a/tests/backend_support/test_pytorch_concatenate_axis_none_contract.py b/tests/backend_support/test_pytorch_concatenate_axis_none_contract.py
new file mode 100644
index 000000000..f8263d7be
--- /dev/null
+++ b/tests/backend_support/test_pytorch_concatenate_axis_none_contract.py
@@ -0,0 +1,48 @@
+import importlib.util
+
+import pytest
+from tests.support.backend_runner import run_backend_code
+
+
+@pytest.mark.backend_portable
+def test_pytorch_concatenate_axis_none_flattens_public_backend_inputs():
+    if importlib.util.find_spec("torch") is None:
+        pytest.skip("PyTorch is not installed")
+
+    result = run_backend_code(
+        "pytorch",
+        """
+import pyrecest.backend as backend
+
+actual = backend.concatenate(([[1, 2], [3, 4]], [[5, 6]]), axis=None)
+
+assert tuple(actual.shape) == (6,)
+assert actual.tolist() == [1, 2, 3, 4, 5, 6]
+print("ok")
+""",
+    )
+
+    assert result.returncode == 0, result.stderr
+    assert "ok" in result.stdout
+
+
+@pytest.mark.backend_portable
+def test_raw_pytorch_concatenate_axis_none_is_patched_with_numpy_backend():
+    if importlib.util.find_spec("torch") is None:
+        pytest.skip("PyTorch is not installed")
+
+    result = run_backend_code(
+        "numpy",
+        """
+import pyrecest._backend.pytorch as pytorch_backend
+
+actual = pytorch_backend.concatenate(([[1, 2], [3, 4]], [[5, 6]]), axis=None)
+
+assert tuple(actual.shape) == (6,)
+assert actual.tolist() == [1, 2, 3, 4, 5, 6]
+print("ok")
+""",
+    )
+
+    assert result.returncode == 0, result.stderr
+    assert "ok" in result.stdout