Keras is a deep learning API written in Python, running on top of the machine learning platform TensorFlow.
Read the documentation at Keras.io.
Multi-backend Keras has been discontinued. At this time, we recommend that Keras users who use multi-backend Keras with the TensorFlow backend switch to tf.keras in TensorFlow 2.0.
Keras 2.2.5 was the last release of Keras implementing the 2.2.* API. It was the last release to only support TensorFlow 1 (as well as Theano and CNTK).
The current release is Keras 2.4.0, which simply redirects to tf.keras.