A major version bump, with the largest change being built in support for ASGI, the Asynchronous Server Gateway Interface, that previously could be included via channels.
The biggest benefits ASGI offers over the traditional WSGI, is the possibility to build asynchronous operations in webapps, and leverage e.g. WebSockets to push information to the client.
Here are the in-development release notes: Django 3.0 release notes – UNDER DEVELOPMENT | Django documentation