When I buy frozen brine shrimp?

Almost certainly dead adults.

The packaging should tell you.

Have a look at them - it should be pretty obvious whether you are looking at eggs of adult dead shrimps.

Most brine shrimp eggs have something written on them, some sort of instructions on how to hatch them.

If they are frozen they will be dead adults, thaw a few out to confirm.

I always buy Hikari frozen brine shrimp so I can only comment on their products, and they are adult brine shrimp. Granted, some are different sizes, but to date (and I have been buying them for years) I have never noticed any eggs whether I buy the cubes or the slabs

adults is all i ever bought