affect code that is relying on certain internal details:
    *   Code that uses `isinstance(x, tf.Tensor)` instead of `tf.is_tensor` when
        checking Keras symbolic inputs/outputs should switch to using
        `tf.is_tensor`.
    *   Code that is overly dependent on the exact names attached to symbolic
        tensors (e.g. assumes there will be ":0" at the end of the inputs,