It looks like I’m out of date. A search revealed that a few Go bots have risen to 4-dan on various online servers, which implies a 4 or 5 stone handicap against a top level player (9 dan).
Found what I was thinking of: here are some game records of a human 9 dan playing two computers with 4 stone handicaps, winning to one and losing to the other (and you can also see a record of the two computers playing each other).
I saw some 4 stone games against experts recently, and thought that 8 stones was the maximum normal handicap.
It looks like I’m out of date. A search revealed that a few Go bots have risen to 4-dan on various online servers, which implies a 4 or 5 stone handicap against a top level player (9 dan).
Found what I was thinking of: here are some game records of a human 9 dan playing two computers with 4 stone handicaps, winning to one and losing to the other (and you can also see a record of the two computers playing each other).