Apple has sent out the official announcement for their Worldwide Developer Conference, which will be held from June 3 to 7. Developers wishing to attend can register for a lottery to get tickets.
In addition to developer sessions, workshops and consultations, the WWDC includes a keynote event where Apple traditionally announces developer-related news such as new macOS and iOS features coming later in the year. We usually find out the name of the next version of macOS and in the past Apple has launched higher-end Macs that are of particular interest to developers.