Google Analytics for various sites around the web are having a new version of Mac OS X show up in their logs. The new version is identified as 10.9, and is likely the beta version of the latest Mac OS X being tested. As you can see in the picture below, 9to5Mac started seeing the new version on October 15.
They report that the IPs associated with the new operating system are coming from Apple's corporate network as well as in the Bay area. The screen resolution on two of the machines, according to 9to5Mac, is the same resolution that the 15-inch MachBook Pro with Retina display uses.
Of course, this could be faked data, but it's likely not the case. If you take a look at the timing and IP addresses, it tells the story. Around now is about the time that beta testing should be occurring for the new operating system and the IP addresses are located where they should be for beta testers.