Microsoft promised to update all compatible Lumia smartphones to Windows 10 Mobile, but the new firmware is still nowhere to be found. There is no official release date either; it's just coming soon.
A Vodafone Italy rep has compiled a list of upcoming updates for the carrier phones and published it on the carrier's official Twitter account. It suggests a bunch of Lumia smartphones will be getting the Windows 10 Mobile sometime next week.
According to the list Lumia 535, Lumia 635, Lumia 735, Lumia 830, Lumia 930, and Lumia 1520 will get an OTA firmware with Windows 10 Mobile between March 7 and March 13. If this is true, this means the global rollout of those updates should happen very soon.
Unfortunately, there is no official confirmation on this dates and Microsoft is still mum on the subject. The Vodafone list is as much of an official source as we have at this point.