Given what is publicly announced, Diotec’s DIW065SIC015 (650 V, TO‑247‑3L, ~ 15 mΩ) seems to be among the very lowest R₍DS(on)₎ in a high‑voltage SiC MOSFET currently available. If your application allows lower voltage rating or smaller package, there may be parts with even lower R₍DS(on)₎ but with trade‑offs.
