Baseline (Widescreen) Solution & Issues
Widescreen resolutions are natively supported; aspect ratio and field of view are automatically detected based on the resolution and can also be adjusted individually. Changes take effect immediately when saved.
As of Update 10, you can now designate a safe-zone for the HUD via the Adjust HUD Margins selection in the Gameplay Options menu.
Ultra/Super-Wide (21:9/32:9) Specific Solution & Issues
Resolutions are available in-game. Aspect ratio can be set manually if Auto does not work.
The Equipment/Warframe menu is stretched from 16:9. Everything else is scaled correctly.
Eyefinity / Surround Specific Solution & Issues
Set aspect ratio to Auto. Aspect ratio may be incorrect after switching from a normal widescreen resolution (restart the game to correct). Some resolutions may require choosing Borderless Fullscreen instead of Fullscreen.
2D loading screens, NPC conversation portraits, and some menu elements are stretched. Everything else scales correctly.
Interactions like hacking are correctly centred. Most menus are centred but some buttons are at the far right of the output. The Equipment/Warframe menus are stretched from 16:9.
The Adjust HUD Margins setting can reduce the HUD area but this does not reduce far enough to have a correctly centred multi-monitor HUD (the multi-monitor screenshot shows the minimum width available). Many other UI elements will ignore this margin setting.
4k UHD Specific Solution & Issues