Apple released the fourth beta of macOS 10.15 Catalina to developers. Beta 4 came two weeks after the launch of the third macOS Catalina beta and over a month after the upcoming macOS update was presented at the WWDC 2019.
The fourth beta of macOS Catalina can be downloaded via the Software Update mechanism in System Preferences.
Identically to all new betas, Apple advises developers not to install macOS Catalina on their primary machines because it is early release software and bugs are inevitable.
In addition, Apple is warning developers about one major incompatibility in the fourth beta of macOS Catalina:
“Using Xcode 11 beta 3 with macOS Catalina beta 4 will prevent SwiftUI previews from working. Update to Xcode 11 beta 4 when it becomes available.”
More detailed information of the upcoming macOS Catalina major improvements can be found here.