The site claims Microsoft's own testers will then vote on which of the next Windows 8 builds will become the "Final Beta," with a voting decision being made on Saturday, January 28th. The final beta build will then be shown at an internal Microsoft preview on Monday, January 30th.
The official pre-beta build number is 8189.0.winmain.120120-1830, and according to the site, the next builds for Windows 8 will be labeled as "Beta Escrow" builds. Additionally, the operating system roadmap claims that the "Final Beta" build to be released to the public will be named "winmain_win8b1." For those enthusiasts patiently awaiting the public release, this is the string to search for on Google when the opportunity presents itself.