Microsoft is simultaneously making available Build 14271 for PCs and Build 14276.1004, the latter only for Windows Phones that originally shipped with Windows 10 Mobile. That means only those with Lumia 950, 950 XL, 650, 550, Xiaomi Mi4 and Alcatel OneTouch Fierce XL. (Other existing handsets will be able to download the Redstone builds once Microsoft updates them to Windows 10 Mobile.)
Both of the new builds contain fixes. The 14276.1004 mobile build also includes a new feature: Support for Visual Voicemail for dual-SIM devices like the Lumia 950 XL.
The PC build includes a number of fixes and updates to the look and feel of Windows 10. There are a number of known issues, including some cases where PCs may freeze or bluescreen when resuming from hibernation. (The suggested workaround is disabling hibernation.)
Head of the Windows Insider program, Gabe Aul, also noted that Microsoft will be locking the feedback setting starting with Build 14271 to "Automatically." If users want to change that setting, they will need to do a roll back to the Windows 10 November update to do so.