Yesterday evening saw the launch of Windows 10 Mobile build 10586.63 on the Fast Ring for Windows Insiders, the third of such cumulative updates for build 10586 following 10586.29 on Dec 5 and 10586.36 released on Dec 17. Initially, it looked like a mistake had been made on Microsoft's part to push it out, with Gabe Aul replying to an Insider that he would "share some more info in a bit about what is going on."

@JCalMN Stand by, I'll share some more info in a bit about what is going on. — Gabriel Aul (@GabeAul) January 8, 2016

About an hour after that, Gabe replied that something had gone wrong with the staging, but that they had corrected it and that the build was now available to all Insiders. With the release of 10586.36 Gabe said that Cumulative Updates would no longer be announced on the Windows Blog, opting instead to make the announcement directly on the Insider Hub.

Luckily for us, an unnamed Microsoft employee has taken to Reddit to share some additional info on the build. According to the poster going by the name of jenmsft, 10586.63 has the following improvements:

Typing on Polish keyboard in Outlook Mail

Turn by turn directions over Bluetooth in car

Battery usage with Iris Reco

Reliability of quick actions settings page

MS Band use with Cortana

jenmsft also noted that 10586.63 has "general reliability, battery and perf improvements that come with each of these revisions," which follows on from the previous release that noted "this Cumulative Update continues to use the minor version for differentiating between each version" which would seem to apply to this build as well.

An announcement for the build is also available on the Insider Hub:

Users have reported - both on Neowin and in the thread on Reddit - that this new build feels snappier and more polished over the previous version, which might indicate that Microsoft is closer to the RTM build of Windows 10 Mobile, which could start rolling for Windows Phone 8.1 devices on Tuesday, January 12 pending carrier approval.

Source: Reddit via WinBuzzer

Update: This article was updated to correct the fact that Cumulative Updates are no longer announced on the Windows Experience Blog.