Apple has just seeded the fourth beta of OS X 10.11.4 El Capitan to developers for testing purposes, two weeks after seeding the third OS X 10.11.4 beta and more than a month after releasing OS X 10.11.3. OS X 10.11.4 has been in testing since January 11. 
OS X 10.11.4 offers a couple of new features, such as Live Photos support in Messages, the ability to password protect notes in the Notes app, and an option to import notes from Evernote, but like the recent OS X 10.11.3 update, it appears to focus primarily on under-the-hood bug fixes and performance improvements. Almost all of Apple’s OS X updates to date have been smaller updates that improve performance rather than introduce new features.
The fourth OS X 10.11.4 beta, build 15E49a, can be downloaded through the Apple Developer Center or via the Software Update Mechanism in the Mac App Store.
As for what’s new in this specific release, that is not known at this time. However, if anything is discovered we will update this post accordingly.
Apple Seeds OS X 10.11.4 El Capitan Beta 4 to Developers