“…Recently, there has been decisive progress on the stable rationality problem, essentially settling this problem in dimension 3, with the exception of varieties birational to a cubic [HKT16], [HT16], [KO17]. These results relied on the specialization method introduced by Voisin [Voi15] and developed in [CTP16], see also [Voi16], [CT18b]. However, little is known about rationality properties of geometrically rational threefolds over nonclosed fields such as finite fields or function fields of curves.…”