AutoML uses  the TF v1 method  b = tf.saved_model.Builder(output_dir)
https://github.com/google/automl/blob/39c39e5b635f73e86082bff3deddefecfbc0a123/efficientdet/model_inspect.py#L338
Object Detection API
Also seems to use the deprecated  tf.saved_model.save
github.com/tensorflow/models/research/object_detection/exporter_lib_v2.py#L278
Model Hub
I have not come so far the I could call model.save() on a trained model.