Resources that were created in the earlier tier model are automatically supported in the new autoscale custom maximum RU/s model. The upper bound of the tier becomes the new maximum RU/s, which results in the same scale range.
For example, if you previously selected the tier that scaled between 400 RU/s and 4,000 RU/s, the database or container now shows a maximum RU/s of 4,000 RU/s, which scales between 400 RU/s and 4,000 RU/s. Then, you can change the maximum RU/s to a custom value based on your workload.