Keras Github: Clarification on files with v1 in their name

I was browsing through the Keras repository and saw that there were files called training_v1.py and training.py

The flow of the code seems to be different in the two and certain edge cases are handled in training.py but arent in training_v1.py

As a person who uses Tensorflow 2 for building models, I wanted to understand what is the difference and whether I should prefer using one file over the other. Also is there a way to pick which file to use for training

This is present in many other files like callbacks etc. So its a bit confusing