With my thief Roland, I was forced to hit 2000 IMM exp to get devious. I'm not sure if that is because there is a threshold for the edge that is 2000 or it just gave me the right amount of edge points to take it. But I had a lot of edges available before I hit 2000, and then I got a 400 exp for an update which took me just over 2000 and thats when devious became available.