Microsoft today released a new cumulative update for Windows 10 PCs and phones, bringing the build number to 10586.494.
KB3172985 is a bit of a mystery at the moment, as Microsoft hasn't published a changelog for either version. Typically, the PC release notes would be published to the Windows 10 Update History page, which isn't currently showing anything new.
The Mobile version is always a bit of a jumble, the release notes sometimes showing up in Microsoft's Answers forum and occasionally, in the Feedback Hub. Perhaps most interesting is that the changelog for phones is almost never available at the time that the update is offered.
Presumably, Microsoft will eventually publish release notes for today's build. When it does, we'll keep you updated.