The fourth beta of macOS 10.12.3 has now been seeded to developers. This comes a few days after releasing the third beta. Because they were released so close together, this update likely fixes issues created with the third build. Right now we’re unsure what’s new with this version. If it follows previous updates, we will likely see bug fixes and performance improvements.
To get this beta developers can go to the Apple Developer Center and find it there. If you aren’t on the beta yet you can go to the Apple Developer Center and download the installer from there.