Lumia 830 users on AT&T are reporting a firmware update for their devices. The update brings change in the Firmware version but there is no impact on the OS version 8.10.15148.160 (GDR2) so it seems to be only a Firmware update pushed by Microsoft.
The new firmware version is 2179.0.15455.24047 which is newer than 2179.0.15213.43037, the firmware brought by the GDR2 update to Lumia 830 and listed officially at Lumia 830 US Page. We reported AT&T pushing GDR2 to Lumia 830 users days ago.
This is not clear what this update brings in terms of changes but we will keep you updated when we come to know more.