Apple today seeded the first beta of an upcoming macOS Mojave 10.14.4 update to developers for testing purposes, a couple of days after releasing the prior update, macOS 10.14.3, which focused on bug fixes.
The new macOS Mojave 10.14.4 beta can be downloaded through the Software Update mechanism in System Preferences after the proper profile has been installed from Apple's Developer Center.
We don't yet know what improvements the next update to macOS Mojave will bring, but it is likely to include bug fixes and performance improvements for issues that weren't able to be addressed in the macOS 10.14.3 update.
What's new in macOS Mojave 10.14.4 - The macOS Mojave 10.14.4 update introduces Apple News in Canada. The update also includes support for automatic dark mode themes in Safari, so if you have Dark Mode enabled and then visit a website that also offers a dark mode, it will be activated automatically.