Prelude (2014)

Prelude was the 2nd place agent in the 2014 Annual Computer Poker Competition instant runoff event. It was the precursor to the Act1 agent.

Playing against Prelude will feel different than playing against any human. It uses an equilibrium strategy, which broadly means that it aims for an unexploitable, defensive style that is effective against any type of opponent. The result is that it plays a wide range of hands in several different ways, sometimes fastplaying, sometimes slowplaying, sometimes betting large, sometimes betting small. It uses all the tactics that people use today, including checkraises, overbets, 3-barrel bluffs, limp re-raising, thin value bets and bluff catches.

Importantly, Prelude never adapts to its opponent and uses the same probability distributions for its decisions each hand. Yet despite the advantage you can achieve by adjusting to it, Prelude makes for a highly competent sparring partner due to how effectively it balances its ranges. To those unfamiliar with game theory, it may be surprising to learn that its strategy is so solid that even knowing how it behaves does not make it easy to defeat.

Prelude is a carefully pre-computed table of 25.5 billion separate probabilities that determine its decision in every possible situation. All of these probabilities were generated by running the Pure CFR algorithm over several weeks. I spent a great deal of time researching and implementing several game solving techniques, and ran hundreds of experiments before choosing the final settings that were used to construct Prelude. That said, I have a long list of future experiments to run.

See this post on the 2014 ACPC results.
See this post to get a sample of the 2014 ACPC hands.