After a bit of a misstep on deployment Microsoft was finally able to get Windows 10 Mobile build 10586.63 out to users in the Fast Ring for the Insider program.
The OS update is considered cumulative and, therefore, does not add new features, but instead focuses on fixes and improvements. Microsoft’s Gabriel Aul, in fact, noted that theses updates are “very targeted changes to fix specific issues” and “Mostly upgrade fixes and other corner-case things per device model.”
Source: ANDRIOD CENTRAL