According to number of reputable sources, Apple is testing Macs running the as-yet-unreleased OS X 10.9 operating system. The reports, from AppleInsider and Mac Rumors point to their site’s visitor logs which show the operating system appear a number of times, with numbers increasing since January.
Although it should be noted that OS identifiers can be faked by visitors, the IP addresses from the logs are associated with Apple and do seem to be in line with Cupertino’s new yearly release cycle for OS X.
Apple announced OS X Mountain Lion around mid-February last year when it released the first developer preview. The official release date was in July, a year on from the launch of OS X Lion in July 2011.