macOS 10.14 Mojave launched yesterday, but Apple already started testing the next version. Developers were just given access to a pre-release beta of macOS 10.14.1.
With availability so recent, it’s not yet known what’s in the new version. That said, the most likely enhancement is the return of Group FaceTime.
Apple promised Group FaceTime would be in Mojave, but pulled the feature out in the middle of the beta-testing process. Presumably, the dev team had decided it wouldn’t be ready at the same time as the rest of macOS 10.14. But the company promised it would be back later this year.