Yesterday, three weeks after the release of the first beta of the third major update OS X 10.11 El Capitan and 48 hours after the release of the second beta iOS 9.2.1, Apple released the second beta OS X 10.11.3 El Capitan.
The update can be installed on any Mac running the previous beta version through the Updates tab App Store for Mac, Developer Program members can also download it through the official developer portal.
The beta version is also available to public testers registered with the Beta Testing Program Apple.
The fresh beta version has build number 15D13b. No official changelog has been released for this beta; Apparently, the update consists of minor technical changes, security, stability and performance improvements and does not bring any new serious functionality to the system. The post will be updated if such features are found.