Hactar is finally retiring well-served Pachi engine for 19×19 boards. The Pachi engine cannot meet modern expectations, where AI easily beats humans. The 9×9 and 13×13 bots are still be Pachi-based, they will be converted to new AI engine later.
New engine is combination of katago engine and a custom model for human-level play. This allows the bot to play very human-like game.
The custom model is trained using human games. As most games were bit older, it mostly plays with somewhat older style. The model seems to be quite good at tactics and ladders. So even if it is weaker than katago, it is not easy to trick.
I will be adjusting the engine further in following days.
Let me know how the new engine feels!
Update: The new engine still bit bad with white and high handicaps. So Pachi is still doing the job for high handicaps.