AlphaGo could probably give it 9 stones and still win, 9p->5d. (Stones go non-linear around the pro ranks, so we can't just count the rank difference in the way we do as amateurs.)
It seems like an indication that either they haven't incorporated the advances of AlphaGo or that Alpha succeeded through the investment of a huge amount of tuning time and processing power rather than through specific advances.
That's too much. Let's say Alpha Go is 9 dan pro or stronger. It would be 4 or 5 stones to a 6 dan amateur, one more stone to 5 dan. Let's say AG is a couple of stones stronger than the strongest humans. Still not nine stones handicap.
