[noonat]

The article is sparse on details, but the linked MIT news article goes into more depth. Of note, the algorithm was able to win 79% of the games it played. Without textual input, it only won 46%, and a more advanced machine learning algorithm without textual input only won 62%. Pretty cool.

[shaggyfrog]

Won those games against whom? Other copies of itself? The weakest built-in AI? The strongest built-in AI? A pseudo-random number generator?

[wlievens]

Built-in AI. They didn't specify the difficulty level, but knowing Civ games (can't speak for FreeCiv though), difficulty levels only tweak handicaps and not the AI algorithms, so the correct choice would be the difficulty level that has no handicap or bonus for the AI.

[pnathan]

Original paper: http://people.csail.mit.edu/regina/my_papers/civ11.pdf

It is a neural network trained, in part, against the text in the game manual.

Of course, it's considerably more complex than that in the theory and implementation. :D