Sony A7s 4K HDMI Greyed Out

I just bought a A7s and was trying to enable the 4K over HDMI. It is greyed out and when you click on it it sais:
This function is currently disabled.
I'm running firmware 1.10

I'm not currently plugged into a 4k capable screen or recording device, but i wouldn't have thought that would prevent me from selecting it?

Would be great to get some advice because i want to make sure i don't have a faulty unit.
 
Does it have to be a 4K recorder pluged in (Shogun/7Q+) or just any HDMI cable? For example if I want to see the 4K output on a 4K TV?


I am asking this because I am going tomorrow to a friend's house who has a 84" 4K LG just to test how the 4K output looks like compared to 1080p, live on the screen. Is that possible?
 
Any HDMI 4K device should work. HDMI cables have a negotiation protocol, so if the A7s "sees" a UHD/4K device at the other end of the cable, it will output a UHD signal.
 
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