Windows 8 currently still in its pre-beta phase of development, has an official build number for 8176. Microsoft is slated to release the Beta of its next version of operating system sometime in late February.
Today, a blog post on Winunleaked claimed to have got hold of Microsoft Windows 8's current development roadmap, which claims that from now to until January 21st, Windows 8 will be considered to be in pre-beta stage. And, on January 23rd, Windows 8 will enter into the Beta Escrow.
After that, begining from Jaunary 23rd to Jaunary 28th, Microsoft beta testers will vote on which build of Windows 8 should go into the Public Beta final build and then sign off the Beta.
The final Beta build the on January 30th, will be shown during an internal preview.
Finally, the article claims the finaly Beta build number will be 8200.winmain_win8b1.