I am looking at building a new hill climb bike cause I have a wild hair somewhere and I am trying to find a Aethos like frame set.  I know the Elves vynar (?) is out there.  I also see that light carbon have a 850g rim brake frame.  are there any others out there in the sub 800g range?

Speeder cycling sc-r48d
Around 850g. I have only one picture of it so i do not really know about their quality or at least read something specifically about that frameset.
Otherwise i consider thr yoeleo r11 as well but their turn around time is quite long

This one is 740g, 28c max tire size, 27.2mm seat post and threaded BSA bottom bracket. I would have bought this frame, but I ended up buying another frame before this one was made available.

https://www.aliexpress.us/item/3256804478469196.html?

This one: http://www.velobuildmall.com/products/vb-r-077-ultra-light-road-racing-bike-frame-with-light-seatost-toray-t-1000-carbon-fiber-our-lightest-frame-ever

Keep in mind any weight claims by a factory/brand is usually for their smallest unpainted frame with no metal hardware installed.

"Frame Weight: 49cm approx 740g±40g（52cm approx 820±40g)"

Meaning a size 55/56 probably weighs around 900±40g unpainted.

My VB-177 size Medium weighs just under 1000g painted. And it uses a BB86 pressfit rather than the horrendous finishing on that BSA threaded BB.