Both screens have a 3840 x 2160 pixel resolution, a contrast ratio of 1000:1 and full 4K at 60Hz input via DisplayPort 1.2 and HDMI 2.0. FreeSync variable refresh rate support is capped at 60Hz though.
The 23.6" panel has a PLS based panel with 4ms gray-to-gray response time, 100% sRGB color gamut coverage, 178 degrees viewing angles, a brightness of 300 nits and maximum power consumption of 34.3W. The 28" version has a TN panel with less color gamut and 170/160 degrees viewing angles (horizontal/vertical) but it offers a maximum brightness of 370 nits and a response time of just 1ms. The power consumption of the 28" panel is listed as maximum 45W.
Both screens come with a warranty of just one year.
Both models feature a 4K (3840x2160) resolution, with FreeSync variable refresh rate support—though at only at a 60Hz maximum—and a static contrast ratio of 1000:1. Full 4K at 60Hz input is supported via the monitor's DisplayPort 1.2 and HDMI 2.0 ports, although FreeSync is a DisplayPort-only affair for now. There's also a secondary HDMI 1.4 port, along with a headphone output. The included stand features only tilt adjustment, although there are VESA mounting holes if you want to improve on that.
Source: The Tech Report