Apple has put OS X Mavericks 10.9.1 pre-release onto the the Developer Center. Registered Mac developers can download it now and begin testing it with their apps. Since pre-release software is under non-disclosure agreement (NDA), we can't report on what, if any, new features may or may not be present, but they'll almost certain come complete with a bevy of fixes and improvements.

No word yet on when 10.9.1 will be pushed out to everyone, but stay tuned!