Season 25 superfinal games 41-50

After 50 games Stockfish leads 14-8 with 28 draws. Stockfish extended its lead to 6 after two game pair wins. There were 3 drawn game pairs, one of them with two white wins. Stockfish won twice in a queen endgame, Leela seems to be struggling in these, its eval is sometimes low when Stockfish already sees the win in its PV. At the half way point of the match Stockfish is leading by 6 wins, not a huge margin after 25 game pairs played. However so far Leela only won a single game pair, so I would say Stockfish is the clear favorite to win the match.

Games 41-42 started in the Scandinavian defense, Mieses variation, played in high level human chess. In game 41 the engines played out a long PV agreement, the black king moved without castling and white castled long. Evals were stable, most minor pieces were exchanged, Stockfish developed its king side rook through the h file. On move 29 the game reached a QRR vs QRR position.

The engines pushed pawns forward and evals started to increase. After a pawn exchange both engines created a passer on the queen side. All the pieces focused on the black e5 pawn, on move 57 the queens were exchanged.

Stockfish gave the e pawn, perhaps to activate its rooks. Leela catured another pawns and pushed two passers forward. Stockfish blocked the passers with its rooks and pushed its passer forward. Leela captured a rook, both engines queened, Leela had the material advantage to force mate.

In game 42 the engines repeated game 41 for 40-plys, this time Stockfish did not exchange its last knight. The engines shuffled for a while, then Stockfish moved the g pawn forward and captured a pawn. Evals started to increase, in a series of exchanges the engines reduced to a double rook ending.

All pawns were passers, Stockfish blocked a captured the black e pawn on the 2nd rank. It had two passers left, with the king support it slowly pushed them forward. Leela tried to avoid a 7-man position but Stockfish forced it when it queened a passer and Leela captured it. There was one white pawn left, the engines continued to play the won 7-man position for more than 30 moves, the game reached a tablebase win on move 135. There were two white wins in this game pair, Stockfish leads 12-8.

Games 43-44 started with a 22-ply rare sideline of the QGD Orthodox defense, Rubinstein variation. The engines castled in opposite directions, all pieces were on the board and the c file was open. In game 43 after a few moves the engines started a long PV agreement, they exchanged queens and a few minor pieces. Evals came down, Stockfish gave two pawns and the game reached a RB vs RB position. Leela was two pawns up with two doubled pawns, Stockfish had an advanced passer and also had a possibility of perpetual check. Evals were low enough for an early adjudication. 

In game 44 Leela pushed pawns on the queen side and placed a rook on the open c file. Evals slowly increased, Stockifsh pushed pawns on the king side. In a long PV agreement Leela gave a pawn, opened the queen side further and the black queen joined the attack.

Stockfish made sure it had enough pieces to defend b2. After exchanging a pair of rooks Leela's attack appeared less threatening. The engines continued to exchange pieces and reduced to a QB vs QB position on move 47. The white king slowly moved forward, the bishops were exchanged on move 59.

Stockfish captured the black b pawn, Leela chased the white king with its queen for a long time. Leela's eval dropped below 1 for a while but then jumped back. On move 102 the white king reached the back rank, Leela started to lose pawns, Stockfish managed to queen a passer and mate. Stockfish wins the game pair, it leads 13-8.

Games 45-46 started in the KGA Bishop's gambit, Cozio variation. Black was a pawn up, the white king moved without castling and black had an eval advantage. In game 45 the engines developed their pieces, then Stockfish gave two pawns, opened the e file and placed a pawn facing the white king on the king side. Leela's (negative) eval jumped, Stockfish captured a pawn back and castled long. In a long PV agreement Leela's eval dropped back, the engines exchanged pieces and pawns until only QR vs QR were left on move 36.

Leela gave the d pawn, its eval was stable while Stockfish's eval steadily increased as it chased the black king to the center. On move 48 the rooks were exchanged, after a while the black h pawn became a passer after a pawn trade. Leela's eva; continued being low, below -0.5 at times as the game progressed. In some of the moves Leela spent a lot of time thinking, yet its eval did not reflect what Stockfish saw as a clear win. On move 76 Stockfish's eval was already over -95, Leela's eval was -.059.

Leela's eval slowly increased finally when Stockfish was already predicting a 7-man win. On move 94 Stockfish captured a pawn, a frew moves later it queened the passer, then it forced mate.

In game 46 Leela castled long early and Stockfish attacked the queen side. Stockfish's (negative) eval dropped, it gave a knight for two pawns and exposed the black king. Leela had to walk its king back to the center and Stockfish pushed a passer to the 7th rank. The black king continued to run to h6, Leela's eval dropped as well and Stockfish pushed a second passer on the queen side. Leela lost a rook for one passer, Stockfish gave a rook for a knight on the king side and exposed the black king to checks again. Evals were low enough and the game was adjudicated. Stockfish wins the game pair, it leads 14-8.

Games 47-48 started with a 23-ply line in the QGD exchange variation. The engines castled in opposite directions, there was only one pair of pawns exchanged, black had an eval advantage. In game 47 Stockfish went a pawn up, (negative) evals came down while the engines exchanged pieces and pawns. On move 28 the game reached a RRB vs RRB position, Leela regained the pawn. Evals were close to 0, after exchanging a pair of rooks the game was adjudicated. In game 48 Leela went a pawn up and pushed pawns on the queen side. Again evals came down as the engines exchanged pieces and pawns. Stockfish regained the pawn, the game reached a QB vs QN position and was adjudicated.

Games 49-50 started with a 20-ply line in the Robatsch (modern) defense. There were no exchanges and white castled long. In game 49 the engines developed pieces and Stockfish castled long as well. Evals came down as the engines played out a very long PV agreement, several pawns and pieces were exchanged and Leela went a pawn up. After the PVs diverged the engines reduced to a QR vs QR position, Stockfish regained the pawn and it had a passer on the king side. The engines shuffled, Leela wouldn't lower its eval, perhaps since the black king was exposed. It lowered its eval with less than 10 moves left on the 50-move counter, the game was adjudicated. Game 50 started with a 53-ply repeat of game 49. After the PVs diverged Leela regained the pawn, the engines shuffled for a while and then reduced to a RN vs RB position. White was again a pawn up but evals were low and the game was adjudicated.

Season 25 superfinal games 31-40

After 40 games Stockfish leads 11-7 with 22 draws. Stockfish extended its lead to 4 wins after winning two game pairs, three game pairs were drawn, one of which had two white wins. In the two game pairs Stockfish won it displayed superior endgame skills. In one game pair the two games reached exactly the same RB vs RB endgame, Stockfish managed to draw as black and win as white. In the other Stockfish won a queen ending which Leela seemed to think was a draw for a long time.

Games 31-32 started with a 24-ply line in the Ruy Lopez, Open, classical defense, played at the highest level of human games. There was one pawn exchange and all pieces were on the board. In game 31 after two moves the engines started to play out a long PV agreement, exchanging most pieces and reducing to a RBN vs RBN position on move 21. Leela was a pawn up, its eval went up for a for a few moves but then came down. The engines traded pawns until all pawns were passers, 3 white on the queen side and 2 black on the king side. Evals were low, after exchanging more pieces the game was adjudicated. 

In game 32 Leela's first move was different, the black king was vulnerable and Stockfish placed a bishop on h6. The engines exchanged all knights in the center, Leela gave a pawn and both engines created a passer, evals started to increase slowly. Stockfish gave the pawn back, the engines exchanged a pair of rooks and Stockfish replaced the bishop on h6 with a pawn. In a series of exchanges the engines reduced to a queen ending with white a pawn up.

Stockfish used checks to improve its position while keeping its pawns safe. Leela's eval did not increase at first, it jumped when the white king moved forward. Stockfish saw the win in its eval, it forced a queen exchange on move 82, then it queened and mated. Stockfish wins the game pair, it leads 9-6.

Games 33-34 started with an 18-ply line in the Ponziani opening, Jaenisch counter attack. The white king side was exposed with the black queen on h3, black had the advantage. In game 33 Stockfish avoided a queen exchange, it castled long while the white king moved without castling. Leela was slow to develop the queen side, though (negative) evals came down. Stockfish created a passer on the king side and pushed it forward while Leela captured a pawn. Stockfish gave a knight and attacked the white king, Leela lost a rook for the passer and the game reached a B vs R ending. Both engines had two pawns on the queen side and Leela had a fortress. Stockfish wouldn't lower its eval for the draw rule, the game was adjudicated only on move 159. In game 34 Leela castled long, the queens were off early and the white king was not in danger. (negative) Evals came down, Stockfish captured pawns on the king side and gave a rook for a bishop. Leela created a passer on the king side and pushed it forward, Stockfish blocked with a rook. In a RBN vs RRN position Stockfish gave two minors for a rook and captured the black passer. Evals were close to 0 and the game was adjudicated. 

Games 35-36 started with a sideline of the Old Indian defense. In game 35 Leela moved its queen forward and captured the b7 pawn, Stockfish tried to trap the white queen. Leela moved a knight forward and captured a second pawn, then gave a rook for a bishop and moved its second knight forward to protect the first knight and to let the queen retreat. Evals came down, there were more exchanges and eventually the engines reduced to a QRB vs QRN position. After exchanging queens the game was adjudicated. In game 36 Stockfish moved its queen forward, it captured two pawns on the queen side and Leela didn't try to stop it. Stockfish exchanged queens, it was two pawns up but its development was slower and its king castled late. Leela moved a rook to the 2nd rank and in a RRB vs RRN position captured one pawn back. Evals came down, the engines continued to exchange pawns and pieces and the game was adjudicated in a rook ending.

Games 37-38 started with a 32-ply line in the Sicilian Dragon, Yugoslav attack. The engines castled in opposite directions, black was a pawn up and the h file was half open. In game 37 Stockfish gave a rook for a bishop early, then it gave another rook for a knight and exchanged queens. On move 29 the game reached a RR vs BN position with black 3 pawns up.

Stockfish tried to block files to restrict the white rooks, Leela gave a pawn and opened the queen side. Stockfish captured all the white pawns but Leela moved its rooks forward and captured pawns. Eventually Leela trapped and captured the black bishop, the game ended in a tablebase win.

In game 38 the engines exchanged bishops and Stockfish moved its queen to h6. The black king was trapped and Leela moved its queen to help it. Stockfish exchanged a pair of knights and regained the pawn, then the queens were exchanged. Stockfish captured another pawn and created a passer on the king side, on move 31 the game reached a RN vs RB position.

Leela blocked the passer with its king. In a long PV agreement the engines exchanged pawns and Stockfish abandoned its passer, though evals continued to increase. On move 51 the remaining pawns were on the queen side, each engine had 3 pawns, the black pawns were all on dark squares and the white pawns on light squares.

Two black pawns were weak and the bishop could not protect them. Stockfish made sure its b3 pawn had enough defenders, slowly it captured black pawns and on move 75 all were captured. Stockfish had two pawns, Leela lost material and the game ended in a tablebase win. There were two white wins in this game pair, Stockfish leads 10-7.

Games 39-40 started with a 20-ply line in the Semi Slav, accelerated Meran variation. Both queens moved forward  on the queen side where a pair of pawns was exchanged. In game 39 the engines played out a long PV agreement, they opened files on the queen side, Stockfish kept its king uncastled. Stockfish gave two pawns and then in a series of exchanges the game reached a RB vs RB position. Leela was two pawns up with no passer and doubled pawns on the queen side. After a while Stockfish managed to captured one of the doubled pawns and formed a strong bishop-pawn pair on the queen side. Evals slowly came down while the engines shuffled, Leela couldn't find a way to improve. There were a few pawn exchanges, Leela was slow in lowering its eval, the game was adjudicated on move 112.

In game 40 the engines repeated game 39 for 72 plys, with transpositions and in some cases slightly different moves. The game reached a RB vs RB position with white a pawn up, and with such a long repeat and evals stable and not high it was obvious the game would have the same outcome. On move 53 Stockfish's eval jumped, but after a pawn exchange a few moves later it came back down. On move 73 Stockfish's eval jumped again, this time it kept increasing. Leela's eval remained low for more than 15 moves, the white king managed to move forward through the center and Stockfish created a passer on move 90.

Leela's eval started to increase while Stockfish already saw the win. Leela captured the two pawns on the king side but Stockfish threatened mate and Leela gave a rook for a bishop. The game ended in a tablebase win with one last white pawn. Stockfish wins the game pair, it leads 11-7.

Season 25 superfinal games 21-30

After 30 games Stockfish leads 8-6 with 16 draws. Stockfish's lead is still 2 wins after each engine won one game pair and there were three drawn pairs, one with two white wins. Leela won its first game pair of the match, adding tension to the match since it is not one-sided and the gap is still small. 

Games 21-22 started with 6-ply line in the Scandinavian, Blackburne gambit. In game 21 the engines played out a long PV agreement, developing their pieces and exchanging a few minor pieces. Leela had a pawn majority on the queen side but it didn't find a way to push the pawns safely. Evals came down, the engines shuffled for a long time. After exchanging pieces the draw rule adjudicated the game on move 79. In game 22 again the engines developed their pieces mostly in PV agreement, and most minor pieces were exchanged. Evals slowly came down, the game reached a QRN vs QRB position with white a pawn up. Stockfish gave a pawn and created a passer, after some shuffling it gave another pawn. Evals were close to 0, the engines continued to exchange pieces and the game was adjudicated.

Games 23-24 started with a 19-ply line in the Sicilian, Scheveningen variation, Keres attack, played in high level human chess. In game 23 the engines castled in opposite directions, in a knight exchange Leela chose to retake with a rook and Stockfish's eval dropped. Stockfish seemed to have the initiative, it was focused on attacking the queen side while Leela blocked and interfered. Evals steadily decreased, Stockfish managed to get a knight to a3 and to open files. It gave a rook for a bishop and moved the queen forward to attack the exposed white king. The game was adjudicated in a QR vs QN position, with perpetual check in the PV.

In game 24 again the engines castled in opposite directions, in the same knight exchange Stockfish retook with a bishop. For a few moves Stockfish offered a bishop and Leela refused to take as it would expose its king to attack. In a series of exchanges the engines reduced to a RBN vs RBN position, Stockfish was a pawn up with connected passers on the queen side but evals were low.

Leela moved its rook forward and captured a pawn, Stockfish's eval started to increase. Stockfish chased the black pieces away and attacked the black king. Leela's eval reacted after 6 moves, the black king had to run forward. After exchanging bishops Stockfish captured two pawns on the king side. Leela had a passer on the king side, Stockfish was only a pawn up but now both evals were over 2.

Stockfish blocked the black passer with its rook and slowly pushed its queen side passers. Leela traded its passer with the white f pawn, and pushed its e passer forward. Stockfish captured the passer with its knight on the 2nd rank, Leela did not take back to avoid a 7-man position. This only delayed the end by a few moves after Stockfish queened a passer. Stockfish wins the game pair, it leads 7-4.

Games 25-26 started with an 18-ply line in the Sicilian Nimzowitsch variation. Both queens were out on the queen side, white was a pawn up with a passer on d6. In game 25 Leela gave a pawn and Stockfish castled long. Stockfish captured the white passer but lost a knight. The engines played out a long PV agreement where the queens were traded and the result was a BN vs R imbalance with high evals.

Stockfish formed a pawn line on the king side and tried to protect the pawns, Leela exchanged a pair of pawns and captured one, creating a passer. After exchanging a pair of rooks Leela traded a knight for the black bishop, leaving a BB vs R ending.

Both engines had a passer but the bishop pair was very strong. Leela captured the black pawns on the king side and blocked the black passer. The white passers were unstoppable, the game was adjudicated after Leela queened.

In game 26 both kings stayed in the center and the black queen retreated. Stockfish lost its passer and it gave another pawn, giving Leela a passer in the center. Evals rapidly increased, Leela captured another pawn but lost a rook by a knight fork. 

Leela's compensation for the rook was the trapped knight in the corner as well as the white rook and bishop on the king side that could hardly move. Leela pushed the passer to d3 and tightened the trap. Stockfish captured the h pawn with its queen and freed its corner knight. It pushed the h pawn and opened a way out for its rook. In a series of exchanges the engines reduced to a RRB vs RB position. 

Leela had connected passers on the 2nd and 3rd ranks but they were blocked, and Stockfish had an extra rook. Stockish gave a rook for a bishop and captured both passers, the game ended in a tablebase win. There were two white wins in this game pair, Stockfish leads 8-5.

Games 27-28 started with a 20-ply sideline of the French, Tarrasch closed variation. In game 27 both kings stayed in the center and there were many early exchanges. Stockfish had a passer in the center, after exchanging queens Leela created a passer on the king side. Evals steadily decreased, Stockfish castled late and blocked the white passer with its king. The game reached a RBB vs RBN position, Stockfish captured the white passer and Leela moved the rook to the 7th rank. Evals were low enough for the draw rule, Stockfish gave a rook for a bishop and the game was adjudicated. Game 28 started with a 30-ply repeat of game 27 with a transposition. Stockfish pushed pawns on the king side and created connected passers there. Leela walked its king to block together with a knight, Stockfish traded a bishop for the knight and the game reached a RRB vs RRB position. The engines shuffled for a while with evals close to 0, after exchanging a pair of rooks the game was adjudicated.

Games 29-30 started with a rare sideline of the semi Slav, accelerated Meran variation. In game 29 the engines formed a diagonal pawn wall that blocked the center and most of the queen side. The engines castled in opposite directions and evals were stable. A few pawn exchanges opened the g file, most of the black pieces moved to the king side to protect the king. All pieces were on the board, the engines shuffled for a while and then Stockfish captured the h pawn on move 38.

With two open files on the king side Stockfish slowly walked its king to the center. Leela's eval increased and it captured the a pawn, Stockfish was less convinced but it had very little time left to think. The engines exchanged all major pieces, Leela captured another pawn and Stockfish tried to hold its position but its eval increased as well. Leela created an advanced passer on the queen side, the engines reduced to a BBN vs BNN position on move 73.

Stockfish's defense collapsed, Leela's pieces moved forward and it managed to capture the black pawns on the queen side. Leela was two pawns up, the white king moved forward and Stockfish couldn't stop the passers. Leela queened and mated.

In game 30 both engines castled short, instead of a pawn wall the engines exchanged pawns and opened the board. Evals came down, the engines exchanged pieces until the game reached a queen ending. Stockfish was a pawn up but with all pawns on the king side. Evals were low enough and the game was adjudicated. Leela wins the game pair, Stockfish leads 8-6.

Season 25 superfinal games 11-20

After 20 games Stockfish leads 6-4 with 10 draws. Stockfish won a second game pair and increased its lead. There were 4 drawn game pairs, 3 with two draws and one with two wins. The Leela version playing in the superfinal seems to be closer in strength to Stockfish than the version that played in the premier division. Leela still has not been able to win a game pair. 

Games 11-12 started with a sideline of the English opening, Great Snake variation. In game 11 the engines played a long PV agreement with all pieces on the board and only one pawn exchange after the start. Evals came down, after move 25 Stockfish gave two pawns and then there was a series of exchanges and the game reached a RB vs RB position with white a pawn up. Leela captured a pawn and created two passers on the king side. Stockfish managed to keep the white king away, after some shuffling Stockfish captured one of the passers. Leela's eval came down enough for the draw rule. Game 12 started with a 22-ply repeat of game 11. Stockfish concentrated on the center, it gave a pawn and opened files, then placed its major pieces there. Evals came down, in a series of exchanges Stockfish regained the pawn. The game reached a RBN vs RBN position, after the rooks were exchanged the game was adjudicated.

Games 13-14 started with a French, Tarrasch variation played in high level human chess. In game 13 Stockfish surprised Leela for a few moves, at first Leela's eval increased as if it thought Stockfish's moves were inaccurate. There were only a few exchanges, Stockfish kept its king in the center. On move 20 Stockfish's eval dropped, Leela's eval dropped after thinking for 8 minutes. In a series of exchanges the engines reduced to a RN vs RB position with white a pawn up. The engines traded pawns, Leela created connected passers on the king side and Stockfish had a passer in the center. Stockfish gave the bishop for the 2 white passers, Leela had one pawn left. Leela shuffled to avoid a 7-man draw, eventually it lowered its eval and the game was adjudicated.

In game 14 Leela castled its king, its eval was low after the start. There were a few pawn and minor piece exchanges, then Stockfish sacrificed a bishop and exposed the black king. Leela's eval jumped, then slowly decreased. Stockfish threatened the black king with its pieces and its eval increased, Leela was satisfied with its defense. On move 28 leela thought for more than 8 minutes and the eval drop suggested it thought that it was safe.

Stockfish played Rd2, seems like a small defensive move, I don't know, but not what Leela expected. Leela thought for almost 15 minutes and its eval jumped to 3. The PVs agreed, there was a series of exchanges and Stockfish gave checks. The end result on move 44 was a QR vs QRN position with white 4 pawns up.  

Stockfish gave checks, protected its king and slowly pushed the h passer forward. Leela exchanged rooks but couldn't prevent a queening and the game ended in mate. Stockfish won the game pair, it leads 5-3.

Games 15-16 started with a sideline of the Sicilian, Sozin attack variation. Game 15 started with a long PV agreement, Leela castled long, Stockfish pushed the b pawn but couldn't open the queen side. Leela captured a pawn and the engines reduced to a double rook ending. Evals came down as the engines traded pawns, after exchanging a pair of rooks the game was adjudicated. Game 16 started with an 18-ply repeat of game 15. A series of exchanges reduced to a RRB vs RRB position and Stockfish went a pawn up. Evals came down as the engines traded pawns, after exchanging bishops Leela's eval slowly decreased and 15 moves later the game was adjudicated.

Games 17-18 started with a rare sideline of the French Winawer, poisoned pawn variation where black defends the g7 pawn with a knight on f5. In game 17 Leela exchanged a bishop for the defending knight and Stockfish moved its king to protect the g7 pawn, blocking its king side rook. Leela captured a pawn, by the time Stockfish freed its rook both engines had a passer on the queen side. The game reached a RRB vs RRB position, the engines traded a pair of rooks and captured both passers, then Leela captured two pawns. Despite being two pawns up Leela couldn't find a way to improve, evals came down and the game was adjudicated. In game 18 Stockfish left the g7 pawn alone, captured a pawn on the queen side and created a passer. Queens were exchanged and evals came down, Leela captured the white passer on the 7th rank. The engines traded pawns and reduced to a RBN vs RBN position. After exchanging rooks the engines shuffled until evals were low enough for the draw rule.

Games 19-20 started with a rare 6-ply sideline of the Philidor defense. In game 19 Stockfish gave a pawn and developed its queen early. The engines played out a long PV agreement, Leela kept its king in the center, there were many early exchanges and the game reached a RRB vs RRB position on move 21. Evals were stable but started to increase after move 27, the engines exchanged a pair of rooks and evals were around 2.

Leela created a passer in the center and supported it with its bishop. Stockfish captured pawns on the queen side and Leela captured pawns on the king side. Leela gave its center passer and replaced it with a passer on the king side. 

Stockfish couldn't stop the white passers advancing, Leela queened and mated.

In game 20 Leela gave a pawn and castled long, Stockfish gave a bishop for two pawns and exposed the black king. The white queen move forward to the queen side facing the exposed king.

The white knight on f3 crossed the board to b5 and joined the attack. Leela traded a bishop for the knight, in a series of exchanges the engines reduced to a RN vs RNN position with white 4 pawns up on move 33.

The endgame was slow. Stockfish focused on the king side first, it traded pawns and exchanged a pair of knights, all the black pawns were eliminated and only the white h pawn remained on the king side. The white king moved forward and protected the queen side pawns, Stockfish slowly pushed the h pawn forward. Leela captured the h pawn on the 6th rank, its king was trapped in the corner and Stockfish mated with its pawns. There were two white wins in this game pair, Stockfish leads 6-4.

Season 25 superfinal games 1-10

After 10 games Stockfish leads 4-3 with 3 draws. The match started with 3 game pairs with a win for both engines, an exciting start to the match. The first draw was in game 7, Stockfish won the reverse and the 4th game pair was the first decisive one. The 5th game pair ended in two draws.

The opening book was created by Jeroen Noomen, details can be found here. Most of the openings were taken from games of chess masters of the past.

Games 1-2 started with a 24-ply line in the Queen's Indian defense, Kasparov variation. In game 1  Leela pushed a pawn to h6, Stockfish grabbed a pawn on the queen side, Leela regained the pawn and exchanged queens in the center. The game reached a RRN vs RRB position on move 27, evals started to increase and the engines exchanged all rooks.

The black bishop had only a few pawns it could target and its own pawns restricted its movement. Leela created passers on both sides of the board and blocked a black passer on the 2nd rank. The black king couldn't defend against all the white passers, Leela queened and won.

In game 2 Stockfish also pushed a pawn to h6, there were many early exchanges that opened the board. The game reached a RRB vs RRN position on move 26, the engines exchanged a pair of rooks and traded pawns. The white king moved forward and both engines created a passer on the queen side.

Stockfish blocked the black king away from the queen side. After exchanging rooks the black king moved to help, Stockfish protected its passer and captured the black passer. The white king switched to the queen side and captured pawns there, the game ended in a tablebase win. There were two white wins in this game pair, the score is 1-1.

Games 3-4 started with a sideline of the KID Saemisch variation. In game 3 there were many exchanges after the start with long PV agreements, evals were mostly stable. Leela captured a pawn and created connected passers on the queen side, after queens were exchanged Stockfish moved a pawn to interfere with one of the passers through a capture. On move 33 the game reached a RN vs RB position. 

Evals started to increase, Leela pushed the a passer while Stockfish created a doubled passer in the center. Leela gave its a passer but captured more pawns and created passers on both sides of the board.

Leela slowly pushed its passers forward, the connected passers on the king side supported each other and eventually one promoted to a queen. Ten moves later the game ended in a tablebase win.

In game 4 Stockfish kept its king in the center and opened the g file. Most pieces stayed on the board, evals increased steadily. Leela gave a rook for a bishop and tried to protect its exposed king with pieces.

Leela tried to counter with a threat on the f file, Stockfish kept the f3 pawn safe to protect its king. Stockfish offered a rook for a bishop but Leela thought it would weaken its defense. After a few moves Stockfish forced the trade and captured a pawn, the engines reduced to a NN vs BN position on move 45. 

Stockfish was a pawn up with a passer, it was confident it was winning but the endgame was long. Leela blocked the passer with its king and protected its isolated pawns. After 15 moves Leela chose to give its bishop for the passer and another pawn. The black king raced to the queen side, there Stockfish trapped it and mated with two knights. There were two white wins in this game pair, the score is 2-2.

Games 5-6 started with a 22-ply line in the Vienna gambit, Fraser-Minckwitz defense, with black a pawn up and white unable to castle, an advantage for black. The black king castled long and there was a white pawn on a6. In game 5 Stockfish gave 3 pawns and opened the king side, with the white king exposed on g3. More pieces joined the attack and (negative) evals increased. The engines exchanged all rooks and Stockfish equalized material, only QNN vs QBN were left on move 33.

Stockfish had a pawn majority on the queen side, it pushed the a and b pawns forward and created a passer. Leela blocked the passer and had to defend against threats to its king and queen. By the time Leela managed to capture the passer Stockfish captured the white g pawn. 

Leela was a pawn up and it chose to give a knight for a pawn, Stockfish immediately saw a win. The queens were exchanged, Leela avoided captures but Stockfish reduced to a 7-man win and mated a few moves later.

In game 6 Stockfish blocked the long diagonal with pawns in the center so the black LS bishop would be less effective. Leela placed a pawn on e3 through a minor piece exchange and gave one pawn to open the king side. Stockfish hid its king behind the black pawn.

Leela attacked the long diagonal to open it, Stockfish moved its king back and captured the black d3 pawn. A series of exchanges reduced to a RBN vs RBB position and Leela centralized its bishops, the remaining rooks were exchanged on move 45.

Material was equal but the black bishop pair was very effective and all the white pawns were isolated. Leela captured a pawn and created a pawn majority on the queen side. It took a while before Leela captured another pawn and created a passer. Stockfish lost material trying to block the black pawns, Leela mated with the bishop pair. There were two black wins in this game pair, the score is 3-3.

Games 7-8 started with a 32-ply line in the Ruy Lopez, Chigorin defense, still played in high level human chess. The center and queen side were blocked except the open a file. In game 7 Leela moved a rook forward on the a file, added a second rook and tried to attack. In a long PV agreement the engines exchanges pieces, evals were stable. On move 43 the game reached a QRN vs QRN position, each engine with 7 pawns. The engines shuffled for a while, Stockfish's eval dropped after Leela moved a pawn on the king side. The engines slowly exchanged pieces and pawns, on move 95 the game reached a knight ending. Leela's eval slowly came down, the game was adjudicated on move 116. 

In game 8 Stockfish moved a rook forward through the open a file and placed it on c6. Leela moved a knight to attack the rook but Stockfish kept it there, and Leela did not take since the result would be a protected passer on c6. Stockish's eval started to increase and it moved pieces to the king side. On move 32 Stockfish offered a knight on the king side, Leela didn't take but its eval dropped.

For 3 consecutive moves Stockfish's move surprised Leela, Leela spent over 4 minutes per move and still its eval remained low while Stockfish's eval jumped. On move 35 Leela finally understood Stockfish's plan, its eval jumped and the PVs agreed. Both the offered white pieces were taken though material was still equal. The black king was in danger, in another series of exchanges the engines reduced to a RB vs RN position with white 2 pawns up. Leela gave another pawn to create a passer in desperation.

The black passer was quick but Stockfish used a back rank mate threat to capture it. Stockfish gained material, queened a passer and mated. Stockfish wins the game pair, it leads 4-3.

Games 9-10 started with a 20-ply line in the Queen's gambit accepted, Godes variation, where white regained the pawn and both queens moved forward. In game 9 there was a long PV agreement starting from move 16. The engines opened the board, exchanged pawns and a pair of rooks and evals came down slowly. Leela grabbed a pawn, Stockfish countered with a threat on the black king and evals dropped close to 0. In a series of exchanges Stockfish gave a rook and a knight for the white queen, the game was adjudicated a few moves later. In game 10 there were no exchanges after the start, Leela gave a pawn on move 24 and a few moves later the queens were exchanged. The engines slowly exchanged pieces and pawns and evals came down. In a series of exchanges the engines traded R for BB and then reduced to a BNN vs RN position. Then engines shuffled and the game ended in a 50 move draw.

Season 25 premier division statistics

A summary statistics table of previous stages and seasons. 

Draw rate, wins

Final draw rate was 52.7%. 

Game termination

The three most common game termination causes were:
42.0% - TCEC draw rule
28.0% - SyzygyTB
19.9% - Mate

There was one crash in the stage, Leela crashed on time, a very rare event.

Moves per game

Median= 69.3
Average= 75.2

There were 43 games longer than 100 moves, the longest was 268 moves (Ethereal - Leela, game 135, draw). 

Time per game (hours)

Median= 2:06
Average= 2:03

Openings

There were variable length book openings in this stage. The first letter of the ECO codes was distributed as follows: 

The engines had almost no freedom to choose the opening variant, all of the game pairs repeated the same ECO code and the opening variant twice.

Reverse pairs, wins

Reverse pairs, same moves

Pairs of reverse games diverged less quickly than usual, 23.8% diverged immediately out of book, 60.7% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 25 plys (Leela - Stockfish, games 306 and 334, Sicilian Velimirovic attack, two draws) 

Season 25 premier division final results

Back from vacation, I am going over the games but with the backlog I'm facing I will be more selective about which games I summarize. This post will cover the last 4 RRs.

Final Standings

Stockfish, Leela, KomodoDragon and RubiChess advance to the playoff stage. Stockfish was dominant from the start, it won 36/42 game pairs without loss, including 3 wins against Leela and 5 against KomodoDragon. 

TBD

Going into the playoff the standings within the top 4 engines are: Stockfish +14, Leela +3, KomodoDragon -3, RubiChess -14.

Interesting games

game 227, Stockfish - RubiChess: The game reached a QB vs RBB position with two pawns left on the king side for both engines. Evals were stable, RubiChess held for a long time but was inaccurate in time trouble and evals started to increase after move 57. Stockfish improved slowly, on move 77 it captured a pawn, then it pushed a passer and traded a pair of bishops. The game ended in mate on move 109.

game 236, Leela - RubiChess: The game reached a RNN vs RR position, the white knights controlled many squares and restricted the black rooks. Leela captured a pawn and created connected passers. RubiChess traded a rook for the two knights but couldn't prevent a queening. The game ended in a tablebase win.

game 242, Stoofvlees - Ethereal: Stoofvlees pushed pawns on the king side and castled long. Evals increased slowly and Stoofvlees opened the king side. Ethereal tried to counter on the queen side, it gave a rook for a knight and two pawns and created passers there. Stoofvlees hid its king behind a black pawn, then reduced to a RR vs RN position. Stoofvlees pinned the black knight and captured it, the gam ended in a tablebase win.

game 247, Ethereal - Leela: The engines reduced to a RB vs RB position, material was equal but Ethereal had a passer on the queen side. Ethereal pushed the passer and moved its king forward as well, it used a mate threat to capture pawns and created more passers. Leela couldn't prevent a queening, game over.

game 248, Stockfish - Stoofvlees: Stockfish was a pawn up in a RB vs RN position with low evals, Stoofvlees was hopeful when it reduced to a rook ending but Stockfish's eval jumped. Stockfish had a pawn majority on the king side, it pushed these pawns forward while Stoofvlees captured two pawns on the queen side. It took Stoofvlees 9 moves to realize it was losing, it lost its rook for the white passers and the game ended in a tablebase win. 

game 250, Leela - Stockfish: Stockfish gave a rook for a knight while the white king moved without castling. Evals slowly increased, Leela attacked through the opne h file and Stockfish walked its king back to the center. Leela gave the material back and the game reached a RB vs RN position. Leela created connected passers, then gave material to promote one to a queen. The game ended in a tablebase win.

Standings after RR9: Stockfish +28, Leela +15, KomodoDragon +8, Ethereal 0, RubiChess -3, Stoofvlees -9, Igel -16, SlowChess -23.

game 254, KomodoDragon - Ethereal: KomodoDragon castled long, it captured a pawn and opened the king side. Ethereal tried to counter on the queen side, as a result KomodoDragon created a passer there. Ethereal stopped the passer on the 7th rank but lost a rook for a knight. KomodoDragon reduced to a king and pawns ending two pawns up, queened two pawns and mated.

game 259, Stockfish - KomodoDragon: KomodoDragon grabbed a pawn with its queen, evals slowly increased. Stockfish used the opening to double rooks on the b file and drive the black queen back. KomodoDragon exchanged pieces and reduced to a RRB vs RRN position. Stockfish went after the isolated black pawns, it exchanged a pair of rooks and captured 3 pawns. KomodoDragon couldn't prevent a queening, the game ended in a tablebase win.

game 266, Leela - KomodoDragon: There were almost no exchanges after the start, the engines played behind their pawn lines with stable evals. The first pawn exchange was on move 51, a few moves later Leela went a pawn up. The engines shuffled and played in blitz mode, evals increased after move 71. Leela gave back the pawn and created two passers, KomodoDragon gave a bishop in desperation. Leela queened a passer and used its material advantage to force mate.

game 270, Ethereal - Stoofvlees: A series of exchanges opened the king side, Ethereal gave a rook for a bishop and pawn and created a passer. Stoofvlees realized it was in trouble in a RBN vs RRN position, Ethereal pushed the passer to the 6th rank and traded a pair of rooks. The white king moved forward, Stoofvlees captured the passer and lost its knight. Ethereal captured all the black pawns and was 4 pawns up, the white pawns moved forward and the game ended in mate.

game 272, KomodoDragon - RubiChess: KomodoDragon pushed pawns on the king side and kept its king uncastled. RubiChess gave a knight for pawns and attacked on the queen side. RubiChess regained the material and the game reached a RB vs RN position, the white king moved forward and captured a pawn. KomodoDragon gave a rook for a knight and created an unstoppable passer, it queened and mated.

game 275, Leela - Ethereal: Leela created a passer on the h file and pushed it to the 6th rank. After queens were exchanged evals started to increase, Leela walked its king to the queen side. After some shuffling Leela opened the king side, it gave the h passer and pinned a bishop, then created a passer in the center. Ethereal captured more pawns but in a series of exchanges lost material and the game reached a RB vs B position. Leela captured black pawns and the game ended in a tablebase win.

game 278, Stockfish - Leela: Stockfish kept its king in the center and opened the h file. It gave a rook for a knight, then sacrificed a bishop and opened the g file. Leela gave a rook back and its king ran to the center, the game reached a R vs N ending. Leela played 13 moves without thinking, its eval was stable while Stockfish saw the win already. Leela slowly increased its eval, Stockfish captured pawns and queened a passer, then mated. 

Standings after RR10: Stockfish +30, Leela +18, KomodoDragon +10, Ethereal 0, RubiChess -3, Stoofvlees -11, Igel -17, SlowChess -27. Stockfish drew game pairs against Leela and Ethereal, Leela also drew is game pair against Ethereal. RubiChess lost to the top3 and only won two game pairs, Ethereal increased its lead to 1.5 points over RubiChess, with one DRR to go.

game 283, Stockfish - RubiChess: Queens were off early, Stockfish was a pawn up with a passer on the queen side. RubiChess regained the pawn and captured the passer but Stockfish created another. RubiChess captured this passer as well but lost a knight. In a RBN vs RB position the black bishop was almost trapped, Stockfish slowly improved and then exchanged rooks. Eventually the game reached a B vs pawns endgame and ended in a tablebase win.

game 286, RubiChess - Stoofvlees: Evals were low until move 39. RubiChess expected a queen exchange but Stoofvlees had other ideas and RubiChess' eval jumped. Stoofvlees decided to give its queen for two rooks, it saw the problem too late. The game reached a QN vs RR position, both kings were exposed but the white pieces were better. RubiChess captured both rooks for the knight and mated.

game 292, Leela - RubiChess: Both engines waited with their castling, RubiChess castled long and Leela opened the queen side while its king stayed in the center. RubiChess hid its king behind a white passer, the engines reduced to a RBN vs RBN position. Leela was a pawn up, it pushed a passer forward supported by its king. RubiChess lost its rook, the game ended in a tablebase win.

game 307, RubiChess - Ethereal: The engines castled in opposite directions, RubiChess pushed pawns on the king side and gave a knight to expose the black king. RubiChess regained the piece and the game reached a knight ending with white a pawn up. Ethereal's eval increased, RubiChess was not convinced at first that it had an advantage. On move 32 RubiChess thought for 23 minutes, all the time it had on the clock. Only on move 55 it felt confident in its win and evals increased. It created a passer, then on move 74 it captured a pawn and created another passer. Ethereal captured one passer but lost its remaining pawns, RubiChess queened and mated.

Standings after RR11: Stockfish +34, Leela +20, KomodoDragon +11, Ethereal -1, RubiChess -3, Stoofvlees -12, Igel -19, SlowChess -30. The only interesting race left is for 4th place between Ethereal and RubiChess. RubiChess beat Ethereal in their direct match, but it is still 1 point behind at the start of the last RR.

game 310, KomodoDragon - Ethereal: Ethereal gave a rook for a bishop, the game reached a QRR vs QRN position and evals started to increase. The engines traded pawns and a pair of rooks, KomodoDragon exposed the black king while its king was safer behind pawns. On move 70 the engines were down to 2 pawns each, KomodoDragon shuffled for a long time. On move 100 the queens were exchanged, the game ended in a tablebase win.

game 315, Stockfish - KomodoDragon: The center was blocked, KomodoDragon walked its king to the king side. Stockfish opened the king side and exchanged all rooks, it captured a pawn and evals slowly increased. The game reached a BN vs BN position, the endgame was slow, it took Stockfish 20 moves to exchange bishops. Stockfish captured pawns and created passers, eventually it queened and mated.

game 317, Igel - Ethereal: Ethereal castled long and Igel pushed pawns on the queen side. Igel gave two pawns and created an advanced passer, it captured a pawn back and opened the queen side. Igel doubled rooks on the open b file, Ethereal lost its queen for a rook and a knight. The game reached a Q vs RB ending, Igel lost its passer but captured black pawns with its queen and created another passer. Ethereal lost its rook, 20 moves later the game ended in a tablebase win.

game 324, Stockfish - Ethereal: Stockfish pushed pawns on the king side, Ethereal gave a knight for two pawns and kept the king side closed. The engines continued to trade pieces and the game reached an unusual BBN vs R position with black 3 pawns up. Stockfish had no pawns left but its pieces were coordinated. It captured two pawns and reduced to a 7-man win, the game was adjudicated 30 moves later.

Standings with 3 rounds to go: Stockfish +36, Leela +22, KomodoDragon +12, RubiChess -2, Ethereal -3, Stoofvlees -14, Igel -19, SlowChess -32. RubiChess closed the gap and is leading Ethereal by 0.5 points. Ethereal's loss to Igel was a surprise. The race for 4th place is wide open with 3 rounds to go including a direct match between Ethereal and RubiChess in the last round.

game 326, Ethereal - Stoofvlees: Ethereal gave a bishop early, then captured a rook and attacked the black king. Stoofvlees had to move its king, it captured a rook for a knight back but evals were already high. Ethereal captured a bishop and reduced to a QBN vs QB position. Ethereal chased the black king all the way to the first rank, eventually Ethereal forced mate.

game 328, KomodoDragon - RubiChess: RubiChess castled long and KomodoDragon pushed pawns on the queen side. RubiChess captured a pawn and used a bishop to block an open file, then gave a rook for a bishop to keep the king side closed. KomodoDragon gave back a rook for a bishop and created two passers. In a QRB vs QRB position KomodoDragon captured two more pawns and RubiChess couldn't block all the white passers. KomodoDragon queened twice and mated.

Two rounds to go Ethereal is leading again with RubiChess 0.5 points behind.

game 331, Leela - Ethereal: There were almost no exchanges after the start, Leela pushed a pawn to h6. Ethereal captured a pawn and Leela created a passer in the center, evals slowly increased. Ethereal blocked the passer on the 6th rank and tried to attack the exposed white king. Leela reduced to a RBN vs RBN position, Ethereal captured pawns and pushed a passer to the 2nd rank but there it stopped. Ethereal lost a rook, both advanced passers were captured and Ethereal was 3 pawns up. The white pieces were stronger, Leela gained more material, queened a passer and the game ended just before mate.

RubiChess beat SlowChess and now it is leading Ethereal by 0.5 points. 

In the last round Ethereal failed to beat RubiChess with white, as a result RubiChess finished 4th and will play in the premier division playoff.