Amazon RDS waits until the "dot-one" release of a new PostgreSQL major version before releasing to general availability. This ensures that all supported extensions and modules (71 in Amazon RDS for PostgreSQL 13) have been updated to work with the new release and with in-place major version upgrades. Amazon RDS releases beta and "dot-zero" versions of PostgreSQL in the Preview Environment, so that customers can start testing and developing against new features in the latest major version.