I'm far from an expert on this stuff, but here's what I'm seeing from personal experience and what I've learned from reading other threads. No, the channels are not 4K, but I didn't expect them to be. I knew that such content is rare, and most likely will be paywalled when it's available..
However the ATSC 3.0 channels with HEVC have other benefits. Apparently the ATSC 3.0 signal is less prone to interference in metro areas. I'm seeing that with the 3 channels I'm now able to tune into, the signal sees stabler, without the occasional glitches I'd see on ATSC 1.0, and the PQ is noticeably better.
For specific numbers:
KTLA and KTTV on ATSC 1.0 were broadcasting at 1280 x 720
And now on ATSC 3.0 they are both broadcasting at 1920 x 1080p
So that's feels like the jump from DVD to Blu-Ray quality.
And it also now supports 10-bit color.
No, it's not "UHD" (4K) but it's still a very noticeable jump in visual quality.
I note that KCOP is still 720p. But it's definitely a stabler signal, compared side by-side with ATSC 1.0. I don't really watch any content on that channel, it's mostly older stuff... probably being upscaled from VHS tape quality...
Here's specs I found in this very detailed thread: discussing Los Angeles ATSC 3.0:
Video
ID : 49 (0x31)
Menu ID : 3 (0x3)
Format : HEVC
Format/Info : High Efficiency Video Coding
Format profile : Main [email protected]@Main
Codec ID : 36
Duration : 22 h 31 min
Width : 1 920 pixels
Height : 1 080 pixels
Display aspect ratio : 16:9
Frame rate : 59.940 (60000/1001) FPS
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 10 bits
Color range : Limited
Color primaries : BT.709
Transfer characteristics : BT.709
Matrix coefficients : BT.709
Also ATSC 3.0 and its HEVC compression for video is about 3-4 times more "efficient" for carrying video data as ATSC 1.0 and its MPEG-2 compression. I'm assuming this means the recordings made in Channels DVR will be smaller.
I'm also now able to pull up a strong KCAL (9.1) signal whereas previously I had a difficult time with that channel specifically. I don't know if that's a result of the HDHR firmware update, some repositioning of the antenna, more bandwidth available or less interference now that wireless signal assignments have changed, or some combination of all of that and maybe more... but, my local channel availability and overall PQ has never been better with Channels DVR and now I'm even happier with it.