diff --git a/bim_vfi_arch/costvol.py b/bim_vfi_arch/costvol.py
index e094dc3..931c6d0 100644
--- a/bim_vfi_arch/costvol.py
+++ b/bim_vfi_arch/costvol.py
@@ -1,12 +1,26 @@
 #!/usr/bin/env python
 
 import collections
-import cupy
 import os
 import re
 import torch
 import typing
 
+cupy = None
+
+def _ensure_cupy():
+    global cupy
+    if cupy is None:
+        try:
+            import cupy as _cupy
+            cupy = _cupy
+        except ImportError:
+            raise RuntimeError(
+                "cupy is required for BIM-VFI. Install it with:\n"
+                "  pip install cupy-cuda12x  (or cupy-cuda11x for CUDA 11)\n"
+                "Or run install.py from the Comfyui-BIM-VFI directory."
+            )
+
 
 ##########################################################
 
@@ -15,16 +29,19 @@ objCudacache = {}
 
 
 def cuda_int32(intIn:int):
+    _ensure_cupy()
     return cupy.int32(intIn)
 # end
 
 
 def cuda_float32(fltIn:float):
+    _ensure_cupy()
     return cupy.float32(fltIn)
 # end
 
 
 def cuda_kernel(strFunction:str, strKernel:str, objVariables:typing.Dict):
+    _ensure_cupy()
     if 'device' not in objCudacache:
         objCudacache['device'] = torch.cuda.get_device_name()
     # end
@@ -216,13 +233,16 @@ def cuda_kernel(strFunction:str, strKernel:str, objVariables:typing.Dict):
 # end
 
 
-@cupy.memoize(for_each_device=True)
-def cuda_launch(strKey:str):
-    if 'CUDA_HOME' not in os.environ:
-        os.environ['CUDA_HOME'] = '/usr/local/cuda/'
-    # end
+_cuda_launch_cache = {}
 
-    return cupy.RawModule(code=objCudacache[strKey]['strKernel']).get_function(objCudacache[strKey]['strFunction'])
+def cuda_launch(strKey:str):
+    _ensure_cupy()
+    if strKey not in _cuda_launch_cache:
+        if 'CUDA_HOME' not in os.environ:
+            os.environ['CUDA_HOME'] = '/usr/local/cuda/'
+        # end
+        _cuda_launch_cache[strKey] = cupy.RawModule(code=objCudacache[strKey]['strKernel']).get_function(objCudacache[strKey]['strFunction'])
+    return _cuda_launch_cache[strKey]
 # end