It was probably already posted before since it's now 5 years old but here is the 108 page long thesis by J.M.P. van Waveren about the Quake III Arena Bot. Interesting read about everything you could possibly know about the bots.

"The Quake III Arena bot is the first commercially developed artificial player that uses fully automated path and route finding through arbitrary complex 3D polygonal worlds, without the need for the bot to acquire knowledge about routing and navigation during gameplay. No human intervention is required to provide the bot with all the information needed to navigate through, and understand new game environments. The bot uses a volume (area) based representation of the 3D game environment, which serves as a back-bone for the bot’s cognitive world model. Together with a high performance path finding solution this cognitive model makes the bot rather resource efficient."

Link (PDF)