This is a list of changes introduced in each release that users should be aware of when migrating from older versions. Most changes are carefully designed not to break existing code; however changes that may possibly break them are highlighted with a box.

## CuPy v2¶

### Changed Behavior of count_nonzero Function¶

For performance reasons, cupy.count_nonzero() has been changed to return zero-dimensional ndarray instead of int when axis=None. See the discussion in #154 for more details.