Below you can find the list of the available OS and firmware updates for Lumia phones with Windows 10.

OS updates:

10.0.10586.164 OS update (March 2016) for Lumia Phones with Windows 10. Key improvements in this release include:

  • Improvements for the reliability of app notifications, including text messages and alarms not ringing as scheduled.
  • Improvements for text message backup to reduce data and battery usage.
  • Fixes for Microsoft Edge with address bar suggestions showing late or persisting during navigation, “Close all tabs” not closing all tabs, and Word Flow on the address bar not functioning as expected.
  • Fix for a problem where the Microsoft account was not detected by the Outlook Mail, Outlook Calendar and People app. Attempting to add a new contact in this state caused the People app to crash for some users.
  • Fix for a problem that caused the Wi-Fi connection to temporarily switch off after prolonged use for some users.
  • Fix for a problem that caused first-party app updates to fail to install successfully for some users, leaving the apps in state where they cannot be launched.
  • Improvements for battery usage, Bluetooth connectivity, and OS reliability.

Source: Newest Mobile Firmware Releases - Microsoft Community

See also: FAQ - Whats New in the latest software update for Lumia phones with Windows 10 (10.0.10586.164/01078.00038.16025.390xx)? - Microsoft - USA