Season 25 entrance league

In season 25 TCEC introduced a new entrance league, but it is just a new name for the qualification league. The Swiss format was abandoned and the entrance league will be a double RR. The 16 engines playing were chosen using the results of the Swiss event that was played earlier.

The engines that will play in the entrance league are:

relegated from season 24 league 2 - Booot, Expositor
played in Swiss season 24 - Smallbrain, Mantissa, MrBob, StockDory, Stash, Weiss, Winter, Equisetum, ChessFighter
new to TCEC - Clover, Caissa, DeepSjeng, Viridithas, BlackCore

Final standings

Viridithas, Clover, DeepSjeng and Caissa advance to league 2. They led the league from the start together with Booot and SmallBrain. Caissa lost twice on time and in the final rounds Booot and SmallBrain came close to it, however a win in the last round secured 4th place for Caissa.

All 4 promoting engines are new to the TCEC leagues. They played in the Swiss event that started the season, their results in the league were better than in the Swiss event which also includes a luck factor.

The 4 advancing engines will play in league 2 together with:
played in season 25 league 1 - BlackMarlin Marvin
played in season 25 league 2 - Uralochka Arasan Wasp Halogen Velvet Tucano

Interesting games

game 1, Caissa - Booot : Caissa used the weak black pawn structure on the queen side, first it went a pawn up and then it captured a second pawn and created two passers. Caissa gave a rook for a bishop to connect the passers, Booot started to lose material but could only capture one passer, Caissa forced mate. 

game 2, Winter - Mantissa: Winter went a pawn up, then gradually reduced to a RBN vs RBN position. Mantissa gave another pawn to free its bishop, after exchanging bishops Winter pushed pawns to win.

game 11, MrBob - Viridithas: The game reached a RRB vs RRB position, the black king was trapped in the corner and it seemed MrBob had the advantage. However, MrBob blundered and allowed Viridithas to exchange the remaining queen side pawns. MrBob was a pawn up but the endgame was a draw.

game 21, Clover - Weiss: After an early series of exchanges lover was up a pawn with connected passers on the queen side. Clover pushed the passers slowly, Weiss managed to separate them but both reached the 7th rank eventually. Weiss lost  a bishop for one passer, Clover queened the other and mated.

game 27, DeepSjeng - Equisetum: After 35 moves the engines opened the center and DeepSjeng went a pawn up. DeepSjeng used threats on the black king to gain an exchange and reduce to a RR vs RN position. The game ended in a tablebase win.

game 32, Winter - Stash: The center was blocked, evals gradually increased while Winter doubled rooks on the open c file. Winter moved a rook forward and traded it for two minors, then opened the king side and attacked the black king. Stash lost material and was mated.

game 33, Stash - Booot: The game reached a RRB vs RBN position with black two pawns up. Booot slowly pushed connected passers forward, Stash pushed a passer to the 7th rank where it was blocked. It took Booot 25 moves to captured the white passer and queen a pawn safely, the game ended in a tablebase win.

game 36, Clover - Mantissa: After the engines opened the position with exchanges the game reached a QRN vs QRB position, pawns were equal but Clover had a passer. Mantissa managed to stop the passer but Clover reduced to a won king and pawns ending.

game 47, Winter - BlackCore: BlackCore captured a pawn but its king was exposed. Winter created a passer and BlackCore lost a bishop to stop it. In a QRN vs QR position Winter attacked the black king, captured the queen and mated.

game 51, Clover - Winter: Winter traded a knight for a rook, but Clover had a passer on the wueen side and the black queen was far on the king side. After exchanging queens Clover gained the material back and the white king moved to support the passer. Winter lost a bishop for the passer, in a bishop vs pawns ending Clover used zugzwang to win.

game 52, Viridithas - Caissa: The game reached a RB vs RB position and was heading for a draw when Caissa blundered and exchange rooks. The bishops were of opposite colors and Viridithas was only one pawn up, but the black king was trapped and the white king was free to support a passer. Caissa couldn't stop a queening, game over.

game 53, Equisetum - Mantissa: Most pieces were on the queen side, Equisetum shifted to attack the black king on the other side. Mantissa gave a pawn and hid its king behind a white passer, Equisetum captured a second pawn and reduced to a QR vs QR position. Mantissa lost more material and was mated.

game 57, Booot - DeepSjeng: The game reached a RN vs RB position with white a pawn up. DeepSjeng could have held perhaps, but it didn't play accurately enough. Booot gave back the pawn, opened the king side and moved its king forward. Eventually it captured a pawn and reduced to a 7-man win.

game 61, Caissa - Equisetum: Equisetum gave a rook for a knight and pawn, Caissa patiently exchanged pieces until only QRN vs QBB remained. Caissa had a passer, after queens were exchanged Equisetum was forced to lose a bishop to stop the passer. The game ended in a tablebase win.

game 68, Equisetum - Winter: Both kings were exposed and under attack, Equisetum had more pieces involved and was more dangerous. After most pieces were exchanged the game reached a Q vs RN position, Equisetum chased the black king away and queened a passer to win. 

game 72, DeepSjeng - Weiss: Weiss gave a knight for two pawns to try to free some space for its pieces. DeepSjeng mostly shuffled for a while, Weiss tried to protect its king and eventually lost a few pawns. DeepSjeng gained more material and queened a passer to win.

game 81, Clover - Booot: Evals gradually increased as the engines exchanged pawns and pieces though material was equal. Booot had two isolated pawns to protect and its pieces were passive. Eventually Clover created a passer and Booot gave a rook for a bishop. Booot couldn't stop the passer without losing more material, game over.

game 87, DeepSjeng - Mantissa: Mantissa was up a pawn but the king side was open and the black king was in danger. The engines shuffled for a long time, when the black king tried to run to the center DeepSjeng moved its pieces forward to attack. Mantissa lost material and was mated.

game 91, Caissa - DeepSjeng: In a drawn opposite color bishops ending Caissa failed to move and lost on time.

game 97, Viridithas - Booot: When the position opened the black king was more exposed and vulnerable. Viridithas used this to capture a pawn and to create connected passers. In a RRB vs RRB position Booot could stop the passers, Viridithas queened to win. 

game 102, DeepSjeng - Winter: DeepSjeng captured a rook for a knight and pawn early in the game, then a series of exchanges reduced to a RN vs R position with black two pawns up. Winter traded pawns but DeepSjeng held on to one last pawn to ensure the win.

game 105, Booot - Mantissa: Mantissa moved its king without castling, blocking its king side rook. Booot sacrificed a knight for two pawns and exposed the black king, Mantissa gave back the piece and the game reached a rook ending with white a pawn up. Booot captured another pawn and queened a passer to win.

game 111, Clover - SmallBrain: The engines gradually exchanged pieces and pawns while evals increased. The game reached a RB vs RN position, SmallBrain could not defend its pawns and Clover captured them all. The two white pawns left were enough to win.

game 112, Viridithas - Equisetum: Evals were stable until move 40 though white was a pawn up. Equisetum gave a rook for a knight, the game reached a QR vs QN position and Viridithas went a pawn up. Equisetum lost its queen for a passer, game over.

Standings after RR1: Viridithas +7, Clover DeepSjeng +6, Booot Caissa +4, SmallBrain +3, Winter +1, Mantissa Weiss 0, Equisetum -1, BlackCore -2, Expositor -4, Stash MrBob -5, StockDory -6,  ChessFighter -8. The newcomers are leading at the half, there are 4 of them in the top 6 engines that are fighting for 4 qualification spots. Winter also started well but then fell back from the leaders.

game 129, SmallBrain - Booot: Evals were stable and the engines mostly shuffled, then on move 44 Booot gave a rook for a bishop. After a few exchanges and more shuffling SmallBrain gave a rook for two knights and opened the position. In a QRN vs QR position Booot was 3 pawns up, SmallBrain captured pawns and reduced to a winning king and pawns ending.

game 137, Booot - Winter: Booot was a pawn up from the start, the engines exchanged pieces and pawns and the game reached a rook ending. Winter could have held perhaps, but in the end the game reached a tablebase win.

game 148, Viridithas - Weiss: Weiss castled long and Viridithas slowly increased the pressure on the queen side. Viridithas pushed pawns and opened the queen side, then used an attack on the black king to capture pawns. The engines reduced to a rook ending with white 3 pawns up, enough for a win.

game 152, Stash - Winter: Stash was a pawn up but evals were stable and the engines shuffled. After move 60 Winter played inaccurately, it let Stash open files and its king was in danger. By the time Winter realized it was in trouble Stash captured a rook for a bishop. The game reached a R vs N ending, Stash queened a passer to win.

game 165, Viridithas - Mantissa: Viridithas gave pawns to open files and attack the uncastled black king. Mantissa was 4 pawns up when Viridithas captured a rook, in a QRB vs QRB position Viridithas chased the black king. Mantissa lost material and the game ended in a tablebase win.

game 167, BlackCore - Winter: BlackCore prepared an attack on the king side, most black pieces waited with only a little room to move. BlackCore opened the king side and a series of exchanges reduced to a QN vs RRN position. Winter gave the knight for a passer, all the pawns were captured and the game ended in a tablebase win.

Standings with 8 rounds to go: Viridithas +10, DeepSjeng +8, Clover +7, Booot Caissa +6, SmallBrain +5, Equisetum +2, Weiss +1, Winter Mantissa -1, BlackCore -4, Stash -5, Expositor -6, MrBob StockDory -9, ChessFighter -10. The top 6 engines are still in the race for qualification. Booot lost to SmallBrain but it used wins against weaker engines to stay in joint 4th place. Equisetum won 3 games and climbed in the table, though it will probably not close the gap to the leaders.

game 180, SmallBrain - Mantissa: After shuffling for a while the engines exchanged pieces and reduced to a RN vs RN position. SmallBrain had a passer on the king side, it captured a pawn and created a second passer on the queen side. SmallBrain exchanged rooks, queened a passer and mated.

game 188, Winter - Equisetum: Winter was up a rook for a bishop and seemed to have an advantage. Then it let Equisetum reduce to a RN vs BN position with the white rook trapped. Evals dropped to 0 and the game was adjudicated a draw. 

game 189, Caissa - SmallBrain: Caissa opened the king side and threatened the black king. SmallBrain was a pawn up but its pieces were on the queen side and struggled to help. Caissa forked the black queen and rook with its knight, SmallBrain escaped but lost two pawns. The pressure on the black king increased, Caissa gained material and the game ended in a tablebase win. 

game 193, Weiss - Booot: Evals increased gradually from the start, material was equal but Weiss had a space advantage. The engines opened files and reduced to a RRN vs RRN position, Weiss created a passer and went a pawn up. After exchanging a pair of rooks Weiss captured two more pawns, Booot gave a knight for one passer and the rook for another, game over.

Standings with 3 rounds to go: Viridithas +12, DeepSjeng Clover +9, Caissa +8, Booot  SmallBrain +6, Equisetum Weiss +3, Winter -1, Mantissa -2, BlackCore -5, Stash -6, Expositor -7, MrBob ChessFighter -11, StockDory -13. The 4 qualification spots are almost decided. Caissa beat SmallBrain and it is holding on to 4th place. Booot also moved a step further away from qualification after its loss to Weiss.  

game 218, Clover - Equisetum: Clover gave a pawn and a bishop to attack the black king. Equisetum gave the material back and the game reached a RN vs RB position. The white rook was on the 7th rank, Clover moved its king forward and captured pawns. Equisetum lost its pieces for passers, game over.

game 223, Caissa - Weiss: Evals increased with most pieces and pawns still on the board. Caissa gave a rook for a bishop to create an advanced passer, then captured a pawn and connected a second passer. However, after some shuffling without a clear plan Caissa failed to move and lost on time. This is its second crash in the league.

Booot and SmallBrain drew their games in round 28, with 2 rounds to go they are now only 0.5 points behind Caissa in 4th place.

Caissa, Booot and SmallBrain all drew their games in round 29, the 4th place will be decided in the last round. Caissa has a head to head tiebreak advantage against both Booot and SmallBrain.

game 233, Booot - Equisetum: Evals increased while the engines exchanged pieces, the game reached a RRN vs RRB position with the black bishop stuck behind pawns. Booot captured a pawn and reduced to a king and pawns ending. The one pawn advantage was enough to win.

Booot still has a chance to finish in 4th place, it needs Caissa to lose (or crash). SmallBrain drew its game and it is out of the race.

game 240, Caissa - Mantissa: Caissa placed a protected knight on e6, Mantissa moved its king without castling. Caissa opened the h file and the black king was in danger, Mantissa exchanged pieces and the game reached a RN vs BN position with white a pawn up. Caissa had connected passers, it gave the rook for a knight and used 7-man tablebases to win.

With this win Caissa finishes 4th ahead of Booot.