The Adrenaline Vault News has a post up quoting Epic's Steven Polge on the subject of AI in Unreal Tournament, describing changes in the bots' behavior at higher difficulty levels, describing the highest level bots like this:

High level bots will also occasionally try to predict respawns of valuable items, such as armor. They also do a better job of using sound to guess where opponents might be. Polge says he is continuing to adjust and improve the AI, so there will be more differences by the time the game ships.

There are more Thief Gold screenshots on Avault as well, but they're the same as the ones linked earlier elsewhere.