Earlier this year, at Worldwide Developers Conference Apple announced OS X 10.9 Mavericks and apple is yet to roll it out to the public. If we believe on rumors, then Apple has internally seeded OS X 10.9.1 builds to its employees. This is nothing new, as expected it does not bring any major features, it only improves performance and fixes bugs.
A rumor suggests that perhaps OS X 10.9.1 might bring the ability to block iMessages and FaceTime calls from certain contacts, though there has been no confirmation of that as yet. Apple hasn’t provided a concrete release date for OS X Mavericks, though it is believed that the launch will take place towards the end of this month through the Mac App Store