Yes, the "waste burner" design. So the entire fuel story revolves around having access to spent fuel which they can reprocess to extract the Pu. Yes, they also

Yes, the "waste burner" design. So the entire fuel story revolves around having access to spent fuel which they can reprocess to extract the Pu. Yes, they also have the thermal design which I'm quite sure requires much lower enrichment, but AFAICT is more a concept than something they're actively developing. It makes sense of course to focus on one design at a time, unless they have infinite money. One of the other fast spectrum MSR startups, Elysium, also proposes using spent fuel + maybe leftover military Pu for startup. The interesting thing about Elysium is that their design at least breeds, so they only need enriched fuel for starting up. They're saying that they can run up to 40 years before needing to reprocess the fuel, just by adding U238 online to the salt.