Leela Chess Zero defeated Stockfish with a score of 106-94 in the final of the 13th Chess.com Computer Chess Championship that finished earlier this week. The match, played on the Chess.com server, saw 26 decisive games.

The final was the culmination of a long event that started on March 10, 2020, and consisted of five stages:

Pentagonals (three minutes + two seconds increment): five engines per pool, top two advance

(three minutes + two seconds increment): five engines per pool, top two advance Triangular (three minutes + two seconds increment): three third-place finishers from pentagonals; winner advances

(three minutes + two seconds increment): three third-place finishers from pentagonals; winner advances Heptagonal (five minutes + three seconds increment): seven engines, top four advance

(five minutes + three seconds increment): seven engines, top four advance Semifinals (10 minutes + three seconds increment): four engines, top two advance

(10 minutes + three seconds increment): four engines, top two advance Finals (15 minutes + five seconds increment): match between two engines

We've already seen one amazing endgame from the semifinals which featured Leela Chess Zero (Lc0), Stockfish, Leelenstein, and Komodo). Eventually, Lc0 and Stockfish made it to the finals which took place April 8-14.

Note that you can find all Computer Chess Championship events in this dropdown.

The final consisted of a match of 200 games, played consecutively, with a time control of 15 minutes with a five-second increment. Book moves were used with variations of different lengths; sometimes only one move was given per side, sometimes 10 or a bit more.

Full 6-man and Syzygy 7-man tablebases were used, and games were played until mate or draw by threefold repetition, stalemate, 50-move rule, or adjudication.

Top-level games among super GMs have a high drawing percentage, and these strong engines facing each other see an even higher percentage of draws. 174 games ended in draws, but that still left 26 decisive games—the ones that are most interesting to look at from a human perspective.

Not taking the draws into account, Lc0 won the match with a 19-7 score. Of the 26 decisive games, only six were won by Black, and of those six, only one black point was scored by Stockfish.

Let's look at a few interesting encounters. For starters, here is game 95, won by Lc0 from a game where only the moves 1.c4 e6 were fed to the engines. As NM Sam Copeland said in his video about the game, "...We see an incredible understanding of space from Leela, and the ability with a flood of pawns on the kingside to create near zugzwang."



NM Sam Copeland takes us through the game.

Game 169, that started as a Staunton Gambit in the Dutch Defense, was absolutely stunning. Lc0's long-term sacrifice of a full bishop on move 16 is just incredible. Eight moves later, Stockfish's queen ends up being trapped. After that, we see a long fight where the material imbalance is queen vs rook and bishop.

Here's the game with annotations, and a video, by IM Danny Rensch:



IM Danny Rensch takes us through the game.

Here's the win that Stockfish scored with the black pieces in game 131. It is quite a fun game to play through because for a long time we once again see Lc0 seemingly calling the shots with an early pawn sacrifice that gives great compensation based on two bishops playing against two knights.

On move 45, Leela gives up another pawn in an attempt to look for more activity, but meanwhile, Stockfish's setup, with knights on f8 and e6, is remarkably solid.

It's unclear what went wrong on move 51 when Lc0 made a wrong queen move that allowed its rook to be trapped. With ingenious play, the engine manages to liquidate to a queen endgame a pawn down, but it loses on move 107.

The match was a clash between a conventional chess engine that implements an advanced alpha-beta search (Stockfish) and a neural-network-based engine (Lc0). In a way, Leela Chess Zero is the open-source version of DeepMind's AlphaZero, which controversially crushed Stockfish in a 100-game match (and then repeated the feat).

More on AlphaZero and deep reinforcement learning, in general, can be found in this recent article.

Below is a game viewer with all 26 decisive games of the match to play through.

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