saver.save(sess, '{}/model.ckpt'.format(flags.model_dir))

As an AI language model, I do not have access to your local files or the context in which this code is used. However, based on the code snippet provided, this line of code saves the TensorFlow session 'sess' and its variables to a checkpoint file named 'model.ckpt' in the directory specified by 'flags.model_dir'. This checkpoint file can then be used later to restore the saved session and its variables.