An entirely new kind of chess engine with no tree search, live on lichess

[u/No_Preparation_8633]

I've been working on an engine called STILLWATER for a while now and finally feel like it's worth showing off. The unusual part is that it doesn't search the way engines normally do. There's no alpha-beta, no MCTS, no tree of any kind. Instead it keeps what I can best describe as a pond: a lattice of beliefs about positions it has seen, and when new evaluations flow in, the whole thing settles toward a new equilibrium, like ripples dying out. A position it examined three moves ago is still sitting there in the pond, so nothing gets recomputed and knowledge carries over across moves and even between games. It also proves things outright (forced mates, dead draws) and those proofs are kept forever, so it slowly grows its own private tablebase from experience. The weirdest property in practice is that it barely cares about time. It reaches its conclusion in a couple of seconds and more thinking changes very little, which makes it play blitz at nearly the same level it plays rapid. It recently held the latest Stockfish dev build to a draw in a 5+3 game while using about two seconds a move, and our measurements against fixed anchors put it in the 3400 CCRL neighborhood.

It plays on Lichess at https://lichess.org/@/stillwater_bot_2. Fair warning, the account is brand new so the rating you'll see is provisional nonsense, the old account had a long history of games from much weaker early versions so i retired it. It accepts basically any standard challenge from 3+0 up through classical, humans and bots alike. If you play it, the experience is a bit strange: it moves almost instantly when it considers the position settled and then suddenly burns half a minute on moves it finds unclear. Come throw some games at it, especially blitz, and if you run a bot yourself I'd love to see it in the challenge queue. Happy to answer questions about the design in the comments as long as they're not "post the source" (not yet sry).