Russian Microsoft site has posted the build information for the winmain compile of 7016: 7016.0.090105-1500, UX Evangelist has also posted following screenshots of newer builds 7015 and 7016. The build string from 7015 is as follows: 7015.fbl_multimedia_media.090104-1750:

The date in the left screenshot is 1/12/2009, so we can gather from this that as of at least January 12, 2009, Microsoft is up to build 7016; 16 builds ahead of the official Beta 1 build 7000. If builds are being compiled daily within that build range, then Microsoft will compile build 7026 on January 15, 2009.

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