Microsoft last pushed Windows 10 Build 10586.318 as May cumulative update to all the PCs running Windows 10 Version 1511 (Build 10586.xxx) and you can read the full official changelog by clicking here. Now the Build 10586.318 is available on Microsoft’s production servers and can be downloaded as CAB files
Microsoft is pushing a new cumulative update KB3156421 for those on Windows 10 Build 10586.218 (Version 1511) currently. The update KB3154879 brings Build 1o586.318 and includes fixes and improvements to enhance the functionality of Windows 10 Insider Preview (Build 10586). KB3154879 (Build 10586.318) Changelog: This update includes quality improvements and security fixes.