In an unusual move that surprised many, Apple released a developer beta of iOS 13.1 yesterday and then a public beta of 13.1 today. However, a final version of iOS 13 has yet to be released. This is the first time Apple has made a move like this.
While there is no official explanation from Apple, maybe see this as a sign that the last release of iOS 13 beta is the one that is being installed on to new devices to prepare them for shipment. New iPhones are expected in weeks. Meanwhile, Apple is preparing to have 13.1 ready as an update on the same day as new devices are available, or perhaps shortly thereafter.
The new beta includes some features that were in earlier betas of iOS 13, or were announced as being part of 13, but had been removed from the beta versions. These include Shortcuts Automations and sharing ETA while using Maps for directions.