by 
Apple has seeded build 13D55 of OS X 10.9.3 for developers to download and test. As of yet, the public beta testers aren’t seeing the new version, so you’ll need to be part of the official developer program to have a look. The new features are covered under a confidentiality agreement so we won’t get into the details here, but the things you expect to be worked on are being worked on — and more.
