In addition to iOS 9.3.2 and watchOS 2.2.1, Apple on Wednesday released the first beta for tvOS 9.2.1 to developers. To update, you'll have to connect your Apple TV 4 to a computer and install the software via iTunes or Apple Configurator.
Todays release comes two weeks after Apple pushed out tvOS 9.2 to the public. That was a significant update, bringing about several user-facing changes such as support for app folders and Bluetooth keyboards, as well as new Siri features.