Yes, it's eight multiplication with the naive algorithm. You can get to seven with a clever trick (Strassen's algorithm). As far as I'm aware, with these precis

Yes, it's eight multiplication with the naive algorithm. You can get to seven with a clever trick (Strassen's algorithm). As far as I'm aware, with these precise numbers (8x8 matrix decomposed into four 4x4) it's unknown if we can do better.