The first major WIN10 update is documented in following links:

http://www.computerworld.com/article/2957258/microsoft-windows/microsoft-issues-first-hefty-windows-10-update.html

https://support.microsoft.com/en-us/kb/3081424

Pushes 325MB update to all Windows 10 devices; will be first test of WUDO

Microsoft today delivered the first large-sized update for Windows 10, a “servicing update” that weighed in at around a third of a gigabyte.  The update, labeled KB3081424 in Microsoft’s identifying scheme, has been pushed not only to Windows Insiders — those who opted in to the firm’s preview program — but also to everyone who has upgraded to the new OS since its launch last week.

KB3081424 was billed as a non-security update: In other words, it did not include patches for vulnerabilities. “This update includes … changes to enhance the functionality of Windows 10 through new features and improvements,” the supporting support document read, using Microsoft’s boilerplate for its bug-fix and feature-change updates. The update was the largest post-launch by far. According to its manifest, the 64-bit version ran approximately 325MB, while the 32-bit version tipped the virtual scale at around 160MB.