Stockfish is the winner of the season 26 superfinal. The final score is 31-17 with 52 draws. In the last five game pairs Stockfish won two and extended its lead to a maximum of +15. Then in the last pair Leela finally managed to win and reduced the gap to +14 in the end. Leela had a chance of a game pair win earlier, but Stockfish managed to win the reverse game 94 in a blitz ending, with what both engines thought was a drawn position on move 90.
Stockfish won the first game pair of the match and it held the lead all the way to the end. It won again before Leela won its first pair, reducing the lead back to +1. Stockfish won 3 more game pairs, then Leela won two, after 14 game pairs Stockifsh led by +2. It seemed at that point that the match would be competitive, but in the next 14 pairs Stockfish won 6 times without loss. The lead was up to +8 before Leela managed to win a game pair. The hope for a Leela comeback, like in season 25, slowly diminished as Stockfish continued to increase the lead in the following games. Stockfish won 8 times without loss in the next 20 game pairs and the lead increased to +15. Leela finally won the last game pair, much too late to change anything. After two superfinals where Leela seemed to close the gap, this season Stockfish again dominated the superfinal.
The first league event of season 26 was the entrance league with 16 engines. There were 5 engines that were new to TCEC and 2 returning engines, including Berserk that was 4th in the premier division of season 24 and took one season off. Berserk dominated the league and won, the newcomer Obsidian and Velvet also qualified comfortably. There was a race for the fourth spot between newcomers Stormphrax and Altair, Altair led two rounds to go but Stormphrax closed the gap and advanced on a tiebreak. In league 2 Berserk and Obsidian again won easily. There were 3 more qualification spots - one more than usual because of SlowChess not starting the season. Several engines were involved in the race, after RR3 Viridithas, Velvet and Arasan opened a small gap ahead of the rest and kept it till the end. In league 1 there were 5 engines that led as a group: Seer, Caissa, Berserk, Obsidian and rofChade. After 3RRs rofChade was dropped but the other 4 engines were almost tied. In the last RR Berserk left the other engines behind to win the league. The other 3 engines ended up in a three way tie, the tiebreak decided that Seer was the second engine to advance.
TBD: premier division, personal
Games 91-92 started with an unusual line in the English opening. In game 91 Leela kept its king in the center and pushed pawns on both sides of the board. The h file opened which was a potential danger for the black king, Leela's eval slowly increased. Leela didn't expect Stockfish's move 19, its eval dropped even though it trapped a black rook. On move 24 the engines started to exchange pieces, starting with a knight for rook trade. Stockfish regained the material and the game reached a RB vs RB position with white a pawn up. Leela wouldn't lower its eval, it gave the rook for a bishop and two pawns, the game continued for 35 more moves. In game 92 Stockfish castled its king, both engines played mostly on the king side. The pawns on the king side moved forward and both kings were exposed. Evals came down despite the fact that Stockfish captured a rook for a knight, the game reached a RRB vs RBN position. After a long shuffle the engines traded minor pieces and the game was adjudicated.
Games 93-94 started with a 22-ply line in the closed Ruy Lopez, Borisenko variation. All pieces and pawns were still on the board. In game 93 there were no exchanges after the start and the engines blocked the center and most of the queen side. On move 22 the engines exchanged minor pieces on the king side and Leela's eval started to increase. On move 27 the first pawns were exchanged on the queen side, opening the a file, Leela then pushed a pawn to h6. Stockfish's eval also started to increase, Leela captured a pawn on the king side and the queens were exchanged.
Leela exchanged pawns in the center and created a passer, then offered a rook for a bishop. Stockfish thought about it but took the rook after a few moves, together with another pawn capture this gave Leela 3 connected passers in the center. Leela was not in a hurry to push the passers forward but Stockfish could not stop them. Leela queened eventually, followed by mate.
In game 94 the engines again blocked the center and there were no exchanges after the start. The first pawn exchange was on move 26 on the queen side, leaving a small opening there. The engines exchanged a pair of bishops, then Leela captured a pawn and opened the b file. Evals were low, the engines blocked the king side and exchanged the remaining bishops. Then there was a long shuffle, on move 88 a pair of rooks was exchanged and the shuffling continued. Stockfish's eval started to increase after move 100, then the engines reduced to a double knight ending.
Leela was a pawn up but its knights could not advance while the white knights had several protected entry points. Leela gave back the pawn and exchanged a pair of knights, giving Stockfish a passer on the king side. Leela gave another pawn in the center, Stockfish gave it back and created another passer. Stockfish reduced to a king and pawns ending and saw the win. Both engines queened but Stockfish gave check first, then queened again and mated. There were two white wins in this game pair, Stockfish leads 29-16.
Games 95-96 started with a rare sideline of the KID Saemisch variation, the center was blocked and all pawns and pieces were on the board. In game 95 the engines exchanged pawns and knights on the queen side. Evals dropped after the black queen moved forward, queens were exchanged and the white king moved without castling. The engines opened the king side, then a series of exchanged reduced to a RB vs RB position. Leela captured a pawn, its eval increased just before adjudication. This only delayed the game's end by a few moves.
In game 96 Stockfish castled its king, the engines exchanged pawns and knights on the queen side and opened the v file. The engines seemed to shuffle but Stockfish's eval slowly increased after move 27, Leela's eval stayed around 1. On move 35 Stockfish pushed a pawn on the king side and exchanged a pair of pawns, then moved major pieces to the g file.
Leela's eval jumped over 2, it tried to defend the g6 pawn with all pieces it could get. The engines exchanged a pair of bishops, Stockfish took its time to get a second rook on the g file and move the queen behind the rooks. Then it moved the pawn to f6 and brought the knight to e7, forcing a knight for rook trade. The g file opened and the game reached a QRB vs QBN position.
Stockfish captured a pawn after exchanging bishops, then it gave the rook for a knight and captured a second pawn. The two pawns advantage was enough for a win in the queen ending, the game ended in mate. Stockfish wins the game pair, it leads 30-16.
Games 97-98 started with a 22-ply sideline in the Sicilian, Scheveningen variation, with all pieces on the board and one pair of pawns exchanged. In game 97 Leela pushed pawns on the king side, a pawn exchange on the queen side opened the a file. Leela captured a pawn and exchanged a pair of rooks, its eval slowly increased. Leela thought Stockfish will exchange pawns on the king side, when that didn't happen Leela's eval dropped. On move 25 the engines started to exchange pawns and pieces, Stockfish gave a bishop and the game reached a QBB vs QB position. Stockfish had connected passers on the king side, Leela gave back a bishop to capture one passer. The white king was exposed and the black queen gave checks until the game ended in a 3-fold repetition.
In game 98 Stockfish thought Leela's first move after book was a mistake. Leela didn't expect Stockfish's response and its eval jumped immediately over 2.5. Stockfish attacked the king side, it sacrificed a knight and then Leela gave its queen for a rook. Stockfish let Leela capture another rook, it had a strong attack on the black king and Leela still had a rook and a bishop undeveloped on the queen side.
Stockfish moved a bishop to h6, Leela offered a rook for the bishop but Stockfish preferred to keep its bishop pair. After trading bishop for knight Stockfish used a mate threat to capture a rook. The game reached a Q vs RB ending, Stockfish pushed a passer on the king side. Leela stopped the passer on the 7th rank, then lost the bishop and the game ended in a tablebase win. Stockfish wins the game pair, it leads 31-16.
Games 99-100 started with the main line of the Czech Benoni defense, the center was blocked and all pieces and pawns were on the board. In game 99 Leela pushed pawns on the king side and the white king went there without castling. Leela's eval slowly increased, after move 19 the engines exchanged pawns and opened the king side. The f file opened and the engines exchanged a pair of rooks on move 29, first piece exchange. Both engines had a passer in the center, more minor pieces were exchanged and both kings were left without any pawns protecting them.
Material was equal but the black e pawn was hard to defend. Leela first got its king to the center for safety, then exchanged queens and only then captured the e pawn. In a RBN vs RBN position Leela exchanged pawns on the queen side and then slowly captured the remaining black pawns. There were two connected white passers left, Stockfish could only delay with checks but eventually Leela queened. Stockfish lost material and the game ended in a tablebase win.
In game 100 the engines exchanged a pair of bishops, Stockfish pushed the h pawn and castled long. More minor pieces were exchanged, Stockfish pushed the pawn to h6 and the engines started to shuffle. Stockfish had a pair of advanced knights, but with all pawns on the board the major pieces could do nothing. On move 62 Stockfish gave a pawn, on move 98 the engines exchanged queens. Shuffling continued with evals at 0, the game was adjudicated on move 167 after enough pieces were exchanged. Leela wins the game pair, Stockfish leads 31-17.
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