The new bug fix was revealed by Windows Insider head Gabriel Aul on Twitter. He did not mention what it contained, but it's safe to day that this download will concentrate on closing some issues that have been detected and reported by the over 5 million testers of Windows 10. Microsoft is also working with its hardware partners like Intel to squash some more bugs before the July 29 launch, including one that could cut the battery life on some laptops.
Update: Turns out one of the fixes in this update is for the 0x80246013 firmware update error many are getting with the Surface 3 and Surface Pro 3!
Source: Gabriel Aul (Twitter)