I'm about to order some hand scraped Brazilian Teak from LL. I had a question from my installer about larger planks cupping. Any advice?

Yes, wider planks are more sensitive to cupping just because of the wider surface area. But cupping is just a natural phenomena, it does not mean the wood is defective or ruined. It is a moisture imbalance between the top an bottom of the plank. This can be eliminated in most cases by keeping the relative humidity within 30% to 50% rh. Unless you have some extra moisture coming up from below. Thats why you need to protect the subfloor moisture from getting to the bottom of the plank, and also not letting the interior rh drop to low.

5" solid braz teak is very sensitive to swings in r/h. I just turned down a 4500 sf job a month or so ago because the homeowner insisted on using that specie . It was really really really hard to do because of the potential money that would have been made but I got burned not once but twice on the same wood installed to the "t" within specs and standards and it still shrank like a wiener in ice water.

Thanks for the info.

if you want to use cumaru,braz teak, braz chestnut buy a engineered one.