Keras Github: Clarification on files with v1 in their name

I was browsing through the Keras repository and saw that there were files called and

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

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