Sig's website is listing it with an alloy frame.

I was under the impression the 10mm's were SS.

Which is correct?

Good question, but assuming that by “SS” you’re referring to stainless steel, it too is an alloy—as are all steels.

When aluminum first became common as the primary metal in certain pistol frames, it was obviously thought that that would seem cheap and flimsy to the ignorant, so gun magazine article writers evidently decided to call it “alloy” even though that word refers to any mixture of metal and other substances.

The frame and slide are stainless on the 10mm.

The magnet will stick both to slide and frame on mine.

Serious side arm right there. Is there a SA model also ?