[fchollet]

Keras is now standalone and multi-backend again. Keras weights files from older versions are still loadable and Keras code from older versions are still runnable (on any backend as long as they only used Keras APIs)!

In general the ability to move across backends makes your code much longer-lived: you can take your Keras models with you (on a new backend) after something like TF or PyTorch stops development. Also, it reduces version compatibility issues, since tf.keras 2.n could only work with TF 2.n, but each Keras 3 version can work with a wide range of older and newer TF versions.