Leela Chess Zero

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Leela Chess Zero
Original author(s)Gian-Carlo Pascutto, Gary Linscott
Developer(s)Gary Linscott, Alexander Lyashuk, Folkert Huizinga, others
Initial release9 January 2018; 19 months ago (2018-01-09)
Stable release
v0.22.0 / 5 August 2019; 7 days ago (2019-08-05)
Repository Edit this at Wikidata
TypeChess engine

Leela Chess Zero (abbreviated as LCZero, lc0) is a free, open-source, and neural network based chess engine and distributed computing project. Development has been spearheaded by programmer Gary Linscott, who is also a developer for the Stockfish chess engine. Leela Chess Zero was adapted from the Leela Zero Go engine,[1] which in turn was based on Google's AlphaGo Zero project,[2] also to verify the methods in the AlphaZero paper as applied to the game of chess.

Like Leela Zero and AlphaGo Zero, Leela Chess Zero starts with no intrinsic chess-specific knowledge other than the basic rules of the game.[1] Leela Chess Zero then learns how to play chess by reinforcement learning from repeated self-play, using a distributed computing network coordinated at the Leela Chess Zero website.

As of August 2019, Leela Chess Zero had played over 232 million games against itself,[3] and is capable of play at a level that is comparable with Stockfish, the leading conventional chess program.[4][5]


The Leela Chess Zero project was first announced on TalkChess.com on January 9, 2018.[1][6] This revealed Leela Chess Zero as the open-source, self learning chess engine it would come to be known as, with a goal of creating a strong chess engine.[7] Within the first few months of training, Leela Chess Zero had already reached the Grandmaster level, surpassing the strength of early releases of Rybka, Stockfish, and Komodo, despite evaluating orders of magnitude fewer positions while using MCTS.

In December 2018, the AlphaZero team published a new paper in Science magazine revealing previously undisclosed details of the architecture and training parameters used for AlphaZero.[8] These changes were soon incorporated into Leela Chess Zero and increased both its strength and training efficiency.[9]

The work on Leela Chess Zero has informed the similar AobaZero project for shogi.[10]

Program and use[edit]

The basis of which Leela Chess Zero has used to self-learn, and play chess at a super human level is with reinforcement learning. This is a machine learning algorithm, mirrored from AlphaZero to be used by Leela Chess Zero, to maximize reward to make the engine a better chess player through self-play.[1][8] From open-source, Leela Chess Zero has played hundreds of millions of games, run by volunteer users, in order to learn with the reinforcement algorithm.[3] In order to contribute to the advancement of the Leela Chess Zero engine, the latest version of the Engine as well as the Client must be downloaded. The Client is needed to connect to the current server of Leela Chess Zero, which all of the information from the self-play chess games are stored, to obtain the latest network, generate self-play games, and upload the training data back to the server.[11]

If, however, someone would like themselves to play against Leela Chess Zero engine, the Network must be downloaded. The Network contains Leela Chess Zero's evaluation function that is needed for the opponent to play against the engine.[11] Playing against a past form of the Leela Chess Zero engine is also possible. Although, the self-play rating calculated for the engine is different from the conventional Elo chess rating. In order to find the self-play rating of Leela Chess Zero from Elo rating is to use the formula:

X = (y + 511.7)/0.6

Where y is the players Elo chess rating, and X is Leela Chess Zero's self-play rating.[12]

Competition results[edit]

In April 2018, Leela Chess Zero became the first neural network engine to enter the Top Chess Engine Championship (TCEC), during season 12 in the lowest division, division 4.[13] Leela did not perform well: in 28 games, it won one, drew two, and lost the remainder; its sole victory came from a position in which its opponent, Scorpio 2.82, crashed in three moves.[14] However, it improved quickly. In July 2018, Leela placed seventh out of eight competitors at the 2018 World Computer Chess Championship,[15] and in the next TCEC season, it won division 4 with a record of 14 wins, 12 draws, and 2 losses.[16] After being promoted to division 3, Leela tied for 2nd place with Arasan, but did not advance. (In the event of a tie, direct encounters between the tied engines decide promotion.) Its record in division 3 was 7 wins, 18 draws, and 3 losses.[16]

In August 2018, Leela Chess Zero had taken first place in the season 13 Top Chess Engine Championship (TCEC), division 4. Leela was 1.5 points ahead of the second place engine, Deus X, powered by the Leela Chess Zero engine, with 20/28 points. Leela had made it into the division three championship to face even stronger opponents with Elo ratings greater than Leela's, along with Deus X with 18/28 points. At first, the Leela Chess Zero engine was winning many games in the early rounds with only a few draws. By round 7, Leela was facing off against the top conventional chess engine in division 4, Wasp, losing the round. Further rounds had Leela needing to gain every point in order to win the Championship and had only gained secure qualification in the final rounds against the other engines. In the end, Leela Chess Zero had 14 wins, 12 draws, and 2 losses.[17] Leela Chess Zero then went on the get 16/28 points in division 3 of the TCEC, losing to Ethereal, with 22.5/28 points, and a direct tiebreak match against Arasan, obtaining third place.[18]

By September 2018, Leela had become competitive with the strongest engines in the world. In the 2018 Chess.com Computer Chess Championship (CCCC),[19] Leela placed fifth out of 24 entrants. The top eight engines advanced to round 2, where Leela placed fourth.[20][21] Leela then won the 30 game match against Komodo to secure 3rd place in the tournament.[22][23] Concurrently, Leela participated in the TCEC cup, a new event in which engines from different TCEC divisions can play matches against one another. Leela defeated higher-division engines Laser, Ethereal and Fire before finally being eliminated by Stockfish in the semi-finals.[24]

In October and November 2018, Leela participated in the Chess.com Computer Chess Championship Blitz Battle.[25] Leela finished third behind Stockfish and Komodo.[26]

In December 2018, Leela participated in season 14 of the Top Chess Engine Championship. Leela dominated divisions 3, 2, and 1, easily finishing first in all of them. In the premier division, Stockfish dominated while Houdini, Komodo and Leela competed for second place. It came down to a final-round game where Leela needed to hold Stockfish to a draw with black to finish second ahead of Komodo. This it successfully managed, and therefore contested the superfinal against Stockfish. It narrowly lost the superfinal against Stockfish with a 49.5-50.5 final score.[27]

In February 2019, Leela scored its first major tournament win when it defeated Houdini in the final of the second TCEC cup. Leela did not lose a game the entire tournament.[28][29] In April 2019, Leela won the Chess.com Computer Chess Championship 7: Blitz Bonanza.[30] Then on May 24, 2019 Leela lost to Stockfish in Computer Chess Championship 8: Deep Dive.[5] It used T42282 neural net in it.[31]

In May 2019, Leela defended its TCEC cup title, this time defeating Stockfish in the final 5.5-4.5 (+2 =7 -1) after Stockfish blundered a 7-man tablebase draw.[32] Leela also won the Superfinal of season 15 of the Top Chess Engine Championship 53.5-46.5 (+14 -7 =79) versus Stockfish.[33][34]

Results summary[edit]

Top Chess Engine Championship
Season Division 4 Division 3 Division 2 Division 1 Division P Superfinal
12 (2018) 8th
13 (2018) 1st 3rd
14 (2018) 1st 1st 1st 2nd 2nd
15 (2019) 2nd 1st
Chess.com Computer Chess Championship
Event Year Time Controls Result Ref
CCC 1: Rapid Rumble 2018 15+5 3rd [35]
CCC 2: Blitz Battle 2018 5+2 3rd [36]
CCC 3: Rapid Redux 2019 30+5 2nd [37]
CCC 4: Bullet Brawl 2019 1+2 2nd [38]
CCC 5: Escalation 2019 10+5 2nd [39]
CCC 6: Winter Classic 2019 10+10 2nd [40]
CCC 7: Blitz Bonanza 2019 5+2 1st [30]
CCC 8: Deep Dive 2019 15+5 2nd [5]
CCC 9: The Gauntlet 2019 5+2, 10+5 3rd [41]

Notable games[edit]


  1. ^ a b c d "Leela Chess Zero: Full Elo Graph". Lczero.org. 7 March 2019. Retrieved 7 March 2019.
  2. ^ "leela-zero". GitHub. Retrieved 27 April 2018.
  3. ^ a b "LCZero". lczero.org. Retrieved 2019-05-28.
  4. ^ "Lc0 Wins Computer Chess Championship, Makes History". Chess.com. Retrieved 2019-05-29.
  5. ^ a b c Pete (pete). "Stockfish Strikes Back, Tops Lc0 In Computer Chess Championship". Chess.com. Retrieved 2019-05-29.
  6. ^ "Announcing lczero". TalkChess.com. Retrieved 11 June 2018.
  7. ^ "Announcing lczero - TalkChess.com". www.talkchess.com. Retrieved 2019-03-21.
  8. ^ a b Silver, David; Hubert, Thomas; Schrittwieser, Julian; et al. (6 December 2018). "A general reinforcement learning algorithm that masters chess, shogi, and Go through self-play". Science. 362 (6419): 1140–1144. doi:10.1126/science.aar6404.
  9. ^ "AlphaZero paper, and Lc0 v0.19.1". 7 December 2018. Retrieved 14 February 2019.
  10. ^ https://github.com/kobanium/aobazero
  11. ^ a b The rewritten engine, originally for tensorflow. Now all other backends have been ported here.: LeelaChessZero/lc0, LCZero, 2019-03-20, retrieved 2019-03-21
  12. ^ "How to Run Leela Chess Engine (LCZero) in Arena at a Specific ELO". Retrieved 2019-03-21.
  13. ^ "Breaking: Leela Chess Zero enters TCEC Season 12". Chessdom. 18 April 2018.
  14. ^ See the season 12 archives at http://tcec.chessdom.com/archive.php
  15. ^ "World Computer Chess Championship 2018". ICGA. Retrieved 19 July 2018.
  16. ^ a b See the season 13 archives at http://tcec.chessdom.com/archive.php
  17. ^ "Leela Chess Zero wins the gold medal in TCEC Div 4 | Chessdom". Retrieved 2019-03-21.
  18. ^ "Ethereal chess engine wins the gold at TCEC Div 3 | Chessdom". Retrieved 2019-03-21.
  19. ^ "Chess.com Computer Chess Championship".
  20. ^ "CCCC stage 2 ended. Leela 4th with a good performance! Stockfish undefeated!". LCZero Blog. 26 September 2018. Retrieved 26 September 2018.
  21. ^ Cilento, Pete (26 September 2018). "Stockfish, Houdini Battle For Computer Chess Championship; Komodo vs Lc0 For 3rd". Chess.com. Retrieved 9 October 2018.
  22. ^ "Leela wins the match series against Komodo and wins a Pawn odds game against Stockfish!". LCZero Blog. 3 October 2018. Retrieved 9 October 2018.
  23. ^ Cilento, Pete (4 October 2018). "Stockfish Wins Computer Chess Championship Rapid; Lc0 Finishes 3rd". Chess.com. Retrieved 9 October 2018.
  24. ^ See the TCEC Cup 1 archives at http://tcec.chessdom.com/archive.php
  25. ^ Cilento, Pete (11 October 2018). "Computer Chess Championship Returns For Blitz Battle". Chess.com. Retrieved 22 November 2018.
  26. ^ Cilento, Pete (19 November 2018). "Stockfish Wins Computer Chess Championship Blitz". Chess.com. Retrieved 22 November 2018.
  27. ^ See the season 14 archives at http://tcec.chessdom.com/archive.php
  28. ^ See the TCEC Cup 2 archives at http://legacy-tcec.chessdom.com/archive.php
  29. ^ "Leela won the TCEC CUP!". LCZero Blog. 4 February 2019. Retrieved 12 February 2019.
  30. ^ a b Cilento, Pete (17 April 2019). "Lc0 Wins Computer Chess Championship, Makes History". Chess.com. Retrieved 18 April 2019.
  31. ^ Olson, Alexis. "Competition Season!". Retrieved 2019-06-22.
  32. ^ See the game score at https://cd.tcecbeta.club/archive.html?season=cup3&round=fl&game=9
  33. ^ "Lc0 won TCEC 15". LCZero Blog. 28 May 2019. Retrieved 28 May 2019.
  34. ^ Högy, Kevin (2 June 2019). "A new age in computer chess? Lc0 beats Stockfish!". chess24. Retrieved 25 June 2019.
  35. ^ Cilento, Pete. "Stockfish Wins Computer Chess Championship Rapid; Lc0 Finishes 3rd". Chess.com. Retrieved 2019-06-20.
  36. ^ Cilento, Pete. "Stockfish Wins Computer Chess Championship Blitz". Chess.com. Retrieved 2019-06-20.
  37. ^ Cilento, Pete. "Stockfish Wins Rapid Computer Championship Over Lc0; Bullet Chess Next". Chess.com. Retrieved 2019-06-20.
  38. ^ Cilento, Pete. "Stockfish Wins Computer Chess Championship Bullet; 'Escalation' Next". Chess.com. Retrieved 2019-06-20.
  39. ^ [1]
  40. ^ Cilento, Pete. "Computer Chess Championship Plays Blitz After Stockfish Defends Title". Chess.com. Retrieved 2019-06-20.
  41. ^ "Computer Chess Championship". Chess.com. Retrieved 9 July 2019.

External links[edit]