He's not going to tell you so I might as well throw around some random speculation.
Heard a rumour of low 7 figures once but figured he's not paying analysts/interns 100k on an AUM of that. Own guess would be low 8 figs, though choice of prime broker implies very low 8 figs that unless there are other factors at play. 7 figs would only make sense if he really was running a really small operation that managed outsize returns because of size.
All just speculation though.