As promised during Monday's WWDC keynote, Apple has issued the first betas of iOS 13, tvOS 13, watchOS 6 and macOS Catalina 10.15 to developers for the first round of external testing.
The builds are available to download from the Apple Developer Center for those taking part in the Developer Beta program. For subsequent beta releases, the updates will also be available as an over-the-air update to devices enrolled in the scheme.
Public beta builds of milestone operating systems will not be offered for testing until July, ahead of an anticipated public release of the software in the fall.
The milestone releases include iOS 13 and its new dark mode, tvOS 13 with additional multi-user support, watchOS 6 with sound level monitoring and enhanced health tracking features, and macOS Catalina 10.15.
The first developer build of iOS 13 is number 17A5492t, the first tvOS 13 beta is build number 17J5485s, the initial watchOS 6 build is 17R5491t, and macOS Catalina 10.15's first build is number 19A471t.
AppleInsider, and Apple itself, strongly recommend users don't install the betas on primary devices or hardware they deem as "mission critical" at all, as there is the highly remote possibility of data loss or other issues. Testers should instead install betas onto secondary or non-essential devices as a safer alternative, and to always make sure there are sufficient backups of important data before updating.