In addition to several other releases, Apple has just seeded the third beta of OS X 10.11.4 to developers for testing purposes, two weeks after seeding the second OS X 10.11.4 beta and three weeks 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 the ability to support password protected notes in the Notes app, but like the recent OS X 10.11.3 update, it appears to focus primarily on under-the-hood bug fixes and performance improvements with few noticeable outward-facing changes. Almost all of Apple’s OS X updates to date have been smaller updates that improve performance rather than introduce new features.
The third OS X 10.11.4 beta can be downloaded through the Apple Developer Center or via the Software Update Mechanism in the Mac App Store.
The consensus is that OS X El Capitan 10.11.4 will be released to the public sometime in early March, alongside iOS 9.3.
Apple seeds OS X El Capitan 10.11.4 beta 3 to developers