Chainer is a deep learning framework written in Python and based on NumPy and CuPy. Though it might not be as widely known outside its specific field, the truth is that Chainer pioneered the define-by-run scheme. Instead of the traditional two-phased approach to train a network, Chainer uses define-by-run to determine a network during the training as it performs the actual calculation.

Chainer is an open source deep learning framework written purely in Python on top of NumPy and CuPy Python libraries. The development is led by Japanese venture company Preferred Networks in partnership with IBM, Intel, Microsoft, and Nvidia.Chainer is notable for its early adoption of "define-by-run" scheme, as well as its performance on large scale systems.