That's a good question - for HP. It is HP's design and only they can tell you what they expose at the HDMI port and what it should be capable of.
If they simply exposed the 'raw' HDMI-configured output from the processor, then you are going to be limited to HDMI 1.4. In this mode, you should be able to get 4K@30Hz, but there are ways that their implementation could limit this further. You really need to talk to them about this.
I personally can't associate 'good' and 'HP' together. What they might do in their hardware designs is completely ruined by their inability to provide a reasonable (minimum 3 years) warranty and a reasonable level of support (including minimum 3 years of driver support and minimum 6 years of BIOS support). I don't know whose support group is worse for dumping their problems on Intel, them or Dell. You pay for this support; you should be demanding that they provide it. You have no warranty of any kind from Intel; your warranty is from HP. When they have a problem and need Intel's help, they have direct paths for escalation and a sales volume for priority; they shouldn't be dumping their problems here - and they certainly should not be making you do it. This is their way of enabling the pocketing of the money that you paid them for support in your original purchase. Shameful.
Off my soapbox now...
...S
