Keras is an open source deep learning library written in python.It is capable of running on the top of MXNet,Deeplearning4j, Tensorflow,CNTK or Theano, Deeplearning4j, Tensorflow, CNTK or Theano. In 2017, Google’s TensorFlow team decided to support Keras in TensorFlow’s core library. Microsoft has been working to add a CNTK backend to Keras as well, and the functionality is currently in beta release with CNTK v2.0 .
There are two types of models available in Keras: The Sequential model and the model class used in functional API. for detail refer: Keras Models.