Season 21 premier division, after RR2

Standings after RR2

The table is divided into two halves. Stockfish is in the lead, and 3 engines are tied for 2nd place. So far only one game pair was decisive within the top 4 engines, Stockfish beating Stoofvlees. At the bottom there are 4 engines within 0.5 points of each other. Again, only one game pair was decisive within the bottom 4 engines, ScorpioNN beat Igel. Two points separate the two halves. Top engines beat bottom engines in 10 of 16 game pairs, without loss.

AllieStein's performance has been below expectations so far (at least my expectation). In season 20 it finished 4th and was considered a part of the leading group. There are still many games to be played, it may yet climb back to the top.

There have been 4/28 game pairs with two white wins so far, 3 of which were within the top 4 engines.

Interesting games

game 1, Stockfish - AllieStein: Stockfish had an eval over 1 from the start. AllieStein moved its queen forward, Stockfish pushed it back to the king side where black pieces surrounded the black king. There were very few exchanges as evals increased, the engines concentrated forces on the king side. The engines opened the king side and both kings were left without pawn support. AllieStein exchanged minor pieces but the major pieces were the danger in the open files. Stockfish was very precise in its moves, AllieStein tried to counter against the exposed white king but Stockfish always had a way out. The engines reduced to a QN vs QN position and AllieStein gave the knight for a passer. Stockfish queened a second passer and mated.

game 4, Stoofvlees - ScorpioNN: Stoofvless had an eval advantage, the center was blocked with all pieces on the board. The engines opened a file on the queen side and one on the king side, Stoofvless went up a pawn. The first piece exchange was on move 43, the engines started to shuffle and nothing seemed to happen for a while. While shuffling evals stated to increase, the engines reduced to a QRB vs QRB position with two white passers facing the black king. ScorpioNN saw it was losing material and just gave up, it sacrificed its pieces and was mated.

game 8, Stockfish - KomodoDragon: There were a few minor piece exchanges after the start, then the engines mainly shuffled and evals stayed a little above 1. Stockfish captured a pawn on move 45, evals started to increase slowly after Stockfish created a passer on the queen side. After Stockfish created a second passer KomodoDragon tried to counter by giving two pawns and exposing the white king to attack. Stockfish kept its king and pieces safe, then reduced to a RRB vs RRB position. With a 3 pawn advantage and two advancing passers the win was a matter of time.

game 10, Leela - Stockfish: On move 26 Stockfish started a series of moves that reduced to a QB vs QB, white two pawns up and with a passer on the 7th rank. Stockfish was sure it was losing with an eval over 3, Leela's eval was less than 1. 

On move 39 Leela continued with its plan and Stockfish immediately dropped its eval to 1. Stockfish thought that Leela should have played 39. c4, and this was Leela's next move. In the game Stockfish was able to exchange queens and reduce to a drawn opposite color bishops ending.

game 13, AllieStein - Ethereal: AllieStein had an eval advantage from the start, evals did not move a lot with most pieces on the board. AllieStein castled long, Ethereal did not castle but its king walked to the king side. Evals started to increase after AllieStein gave a pawn to open the king side. Ethereal captured a second pawn but the white major pieces threatened its king. In a series of exchanges AllieStein gained a knight and the game reached a RB vs R ending with black two pawns up. After exchanging rooks AllieStein used zugzwangs to capture the black pawns, the game ended in a tablebase win.

game 15, Stockfish - Stoofvlees: Stockfish's eval increased very quickly from the start, it thought Stoofvlees was not worried enough about its king. Stockfish weakened the black king side pawns with a pawn on h6, then it attacked the back king while its eval already showed a mate score. Stockfish created a passer with a knight sacrifice, it chased the black king away and queened the passer. Stoofvlees captured a rook but with two white queens chasing the black king mate came very quickly, on move 35.

game 16, KomodoDragon - Leela: KomodoDragon gave a pawn and opened the g file. The black king was stuck in the center and unable to castle, KomodoDragon's eval started to increase. The black king ran to the queen side, Leela thought it was safe enough and its eval did not change. The engines reduced to a QRB vs QRB position, Leela started to feel the danger after KomodoDragon opened the queen side. The white queen and rook danced on the board, KomodoDragon captured a pawn and then another. Finally an attack on the king led to a QB vs RB position and mate.

game 22, Stockfish - Ethereal: Stockfish pushed a pawn to h6 and trapped the black DS bishop in the corner. Evals increased rapidly, the engines opened the queen side and each side had two passers. The black passers were connected but the white passers were more dangerous. Stockfish calculated mate when both passers were on the 6th rank. Ethereal gave its queen for a rook to capture one passer. It lost all its remaining pieces, except the trapped bishop, for the other passer. Mate followed quickly.

game 23, KomodoDragon - ScorpioNN: The engines played behind their pawn lines with very few exchanges. KomodoDragon gave a pawn to open the king side, evals increased as it attacked the black king. ScorpioNN had no pawn support for its king, it lost a piece defending and the game reached a QN vs Q position. KomodoDragon continued to attack the exposed black king, the black passers were too far to be a threat. ScorpioNN eventually lost its queen and was mated.

game 24, Leela - Stoofvlees: Leela pushed a pawn to h6 and trapped the black DS bishop in the corner. The engines opened a file on the queen side, there were very few exchanges and evals remained stable. Leela placed a rook on the 7th rank and a few moves later evals started to increase. Stoofvlees exchanged a pair of rooks and Leela went a pawn up creating a central passer. The engines reduced to a QN vs QB position, Leela soon had 3 advancing passers. The black queen captured a few pawns but couldn't stop all the white passers, it didn't take Leela long to mate.

game 25, Stoofvlees - AllieStein: The game reached a RRN vs RRB position on move 52 with evals around 1. Stoofvlees went a pawn up, after exchanging a pair of rooks evals started to increase very slowly. AllieStein gave its last pawn and causing the last two white pawns to be doubled. Stoofvlees was careful not to reduce to a drawn endgame, eventually AllieStein captured one white pawn. However it saw was about to lose and allowed a mate in 1.

Standings after RR1: Stockfish +4, KomodoDragon +1, Stoofvlees Leela Igel 0, AllieStein -1, ScorpioNN Ethereal -2. Stockfish has a promising lead, still very early in the league. Igel drew all its games so far.

game 34, Stoofvlees - Ethereal: Stoofvlees had an eval advantage that increased from the start. The queen side was blocked and the black pieces had little room. Ethereal opened a file in the center and gave a rook for a knight and two pawns. Stoofvlees reduced to a RB vs BN position, then created an advanced passer on the queen side. Ethereal had a passer on the king side but the white king was on time to block it. Ethereal had to deal with more white passers and couldn't prevent a queening and a win for Stoofvlees.

game 35, Leela - Igel: The game reached a R vs N ending on move 40, Igel was a pawn up and evals were around 1 and stable. On move 41 Igel blundered and Leela's eval jumped over 5. Igel saw the problem a few moves later, Leela started to capture pawns, then won with its passers.

game 36, KomodoDragon - Stockfish: Stockfish's develpment was slow, its queen grabbed a pawn and moved forward, then it castled long without full pawn support. KomodoDragon regained the pawn, then traded a knight and two pawns for a rook. KomodoDragon's pieces were strong in the open board, it targeted the black queen and then started to chase the black king to the center. In a series of exchanges KomodoDragon won a piece and reduced to a BB vs N position. The last white pawn secured the win. There were two white wins in this opening.

game 41, Ethereal - AllieStein: The black king remained in the center unable to castle. After AllieStein moved its king to the king side and some shuffling the engines opened a file in the center and Ethereal went a pawn up. Ethereal had a pawn majority on the queen side, after exchanging bishops it created an unstoppable passer. AllieStein gave as many checks as it could, but Ethereal had two queens and it mated once there were no more checks. There were two white wins in this opening.

game 42, ScorpioNN - Igel: Evals were over 1 and there were only a few exchanges after the start. The black king was left without pawn support, evals increased as the engines reduced to a QRB vs QRB position with white a pawn up. After exchanging queens ScorpioNN captured a second pawn. Igel gave its bishop to stop a passer, the last white pawn gave ScorpioNN the win.

game 44, Leela - KomodoDragon: KomodoDragon gave a rook for a knight and pawn, evals started to increase as Leela exchanged pieces. The game reached a RB vs BN position, Leela created an unstoppable passer to win. There were two white wins in this opening.

game 52, Stoofvlees - Leela: See featured game below.

game 54, Leela - ScorpioNN: The game reached a RN vs RB position with evals under 1. ScorpioNN had 2 passers on the queen side and Leela had 2 passers on the king side. Leela thought ScorpioNN's decision to move its king towards the center was a mistake, it allowed the white rook to block the black king away from the white pawns. Leela's eval jumped after another ScorpioNN blunder, this time it did not push a passer. This gave Leela the advantage in the passer's race for promotion, it won a rook for a knight as a result. The R vs B ending was a win for white.

game 55, KomodoDragon - Ethereal: Evals were over 1 from the start, the black queen grabbed an early pawn and retreated to the king side. Evals jumped after Ethereal missed KomodoDragon's move 21, in a series of exchanges KomodoDragon reduced to a QRN vs QRN position with an advanced white passer in the center. Eventually Ethereal lost a piece for the passer, and the game reached a winning knight vs pawns ending. 

game 56, Stockfish - Igel: The center was blocked and evals were under 1 for a long time. Evals increased a little after Igel gave a pawn and opened the queen side. Stockfish had a passer, after reducing to a QBN vs QNN position Stockfish pushed the passer forward one square. The engines exchanged queens and this created a second white passer. Stockfish gave a pawn and pushed its first passer to the 6th rank, Igel used its knights to keep the white passers away from promotion. Stockfish exchanged a pair of knights, Igel captured the white passer in the center but by then Stockfish had passers on both sides of the board. The black king couldn't cover them all, Stockfish queened a pawn and won. 

Featured game: Stoofvlees - Leela
Premier division, game 52
Link to game on TCEC

Evals slowly came down after the start. The engines castled in opposite directions, Leela opened the king side and then gave a rook for a knight and pawn to created a passer. The engines exchanged pieces and opened the position. Leela captured a second pawn and created another passer. On move 44 Leela thought for over 9 minutes and its eval jumped close to 2, quite unexpected.

Stoofvlees expected this move in its PV, and it continued as it planned exchanging the rooks. According to Leela's PV a different continuation could have been better for Stoofvlees. Evals came down again and the game continued. In a QR vs QN position Stoofvlees used the exposed black king to clear the black pawns on the queen side and create connected passers. This time both evals increased, after exchanging queens only R vs N remained.

Stoofvlees pushed its passers forward. Leela moved its king forward and captured the rook for a passer. The remaining pawns raced forward and both engines promoted a passer simultaneously. Stoofvlees captured the knight, Leela saw it was losing and underpromoted to a rook. The game ended in a tablebase win a few moves later. There were two white wins in this opening, though the games were not similar.

Season 21 league 1 statistics

A summary statistics table of previous stages and seasons.  

Draw rate, wins

Final draw rate was 58.0%. 

Game termination

The three most common game termination causes were:

41.1% - TCEC draw rule
33.9% - SyzygyTB
20.5% - Mate

There were no crashes in the stage.

Moves per game

Median= 67.5
Average= 70.0

There were 10 games longer than 100 moves, the longest was 151 moves (SlowChess - rofChade, game 90, draw). 

Time per game (hours)

Median= 1:37
Average= 1:35

Opening

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

The engines had a little freedom to choose the opening variant, 96.5% of the game pairs repeated the same ECO code twice, 94.6% repeated the same opening variant twice. All game pairs repeated the first letter of the ECO code.

Reverse pairs, wins

Reverse pairs, same moves

Pairs of reverse games diverged quickly, only 25.0% diverged immediately out of book, 53.6% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 7 plys (RubiChess - Nemorino, games 5 and 33, QGD Chigorin defence, Janowski variation, two draws) 

Season 21 league 1 final results

I was sad to hear that Guy Haworth died last week. Guy was a reader of this blog, I suppose one of the few who read through my statistical reports where he would sometimes comment and point out an error I made - for which I was thankful. Together with Nelson Hernandez (Cato) he wrote the summary articles of TCEC seasons that can be found on the TCEC website, their writing skills obviously better than mine. I always got mentioned in these summaries, for which I'm also greatful. During season 20 I reached out to Guy and we corresponded a few times by mail. He was very friendly and easy to talk to, both about computer chess and about personal matters. I didn't know he would be gone a few months later.

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Final standings

Igel and Ethereal advance to the Premier division. Igel started strong, it led the table at the half with a +5 score without loss. In the second half it lost 3 games, yet it won 5 and held on to first place. Ethereal only had a +1 score at the half, it secured 2nd place with a +5 score in the second half of the league. RubiChess was their only competitor but it couldn't keep up with the leaders and ended in 3rd.

rofChade and Nemorino are relegated back to league 2. The race at the bottom of the league was very tight to the very end. rofChade had a -4 score at the half, it was alone in last place and appeared to be weakest. In the second half it performed better while other engines lost games. Pedone and Nemorino in particular dropped down, and together with Xiphos formed a group of 4 engines fighting for survival. The standings were determined only in the last few rounds, with rofChade losing to Xiphos on a head to head tiebreak.

Ethereal dropped from the premier division to league 1 on season 19, in season 20 it qualified for the premier division and was relegated again. It may repeat this in season 21. On the other hand rofChade also qualified for the premier division and was relegated in season 20, this season it is relegated to league 2. A little bit surprising, it shows that it is very hard to keep up unless you keep improving.

The final draw rate was 58%, there were 5/56 openings where both engines won a game. Biased but much less so than in season 20.

Igel and Nemorino will compete in the premier league together with:
Stockfish, Leela, KomodoDragon, AllieStein, Stoofvlees, ScorpioNN, all played in the season 20 premier division.

Interesting games

game 57, Pedone - RubiChess: RubiChess was a pawn up from the start, while Pedone had a bishop pair advantage. Pedone created a passer on the queen side in a RRB vs RRN position, then pushed it forward. The engines reduced to a rook ending, the white passer was on the 7th rank and RubiChess pushed a passer in the center to the 2nd rank as well. Both passers were removed leaving pawns only on the king side. One white pawn was isolated and vulnerable, the white king was too far to help. Once RubiChess captured the white pawn it had enough material to win.

game 59, Igel - rofChade: rofChade had an eval advantage of around (negative) 1 from the start. The engines exchanged pieces until reaching a rook ending. All the white pawns were isolated, rofChade gradually captured them. Igel was always one pawn behind until it was left with one last pawn. rofChade found the right moves to capture the white pawn while keeping two of its own, resulting in a tablebase win.

game 61, RubiChess - Nemorino: RubiChess attacked on the king side, it exposed the black king with a rook sacrifice. To get its king out of trouble Nemorino had to give material back and the game reached a NN vs R imbalance. RubiChess picked up isolated black pawns and reduced to a BNN vs RB position. Nemorino lost its bishop for an advanced passer, the remaining white pawns gave the win to RubiChess.

game 64, Pedone - Ethereal: Pedone had an eval advantage from the start in a closed position without queens. The engines opened the center with a few exchanges, Ethereal created a king side passer and evals came down. Ethereal gave a rook for a bishop, it lost its king side passer and created another on the queen side. Evals turned negative in a RRB vs RBN position with a black passer on the 3rd rank. Pedone saw the problem too late, it gave the bishop to clear the black pawns on the queen side. In a patient endgame Ethereal captured the white pawns, and the last black pawn secured the tablebase win.

game 65, Ethereal - RubiChess: Ethereal started with an eval advantage that increased steadily. The black LS bishop was trapped and it also blocked the queen side rook. By the time RubiChess opened a path for its bishop Ethereal had connected passers on the king side. In a an attempt to find a counter RubiChess gave two pawns to create a passer, then gave a rook and bishop to queen the passer. Ethereal used its rooks to clear the remaining black pawns, then gave both rooks and queened a pawn. The remaining QN vs Q ending with 3 pawns was a win for white.

game 66, Igel - Pedone: Evals stayed around 1 for a long time with most pieces and pawns still on the board. Pedone tried to open the queen side, it created two pawns but something went wrong and Igel captured both. The black king became vulnerable on the back rank, Igel used this to reduce to a Q vs RN ending. The black pieces were soon captured using fork attacks, game over.

game 72, Ethereal - Igel: Ethereal started with an eval advantage. It went a pawn up and created a passer on the queen side. After exchanging queens evals were around 2 for a while, Ethereal connected a second passer and the game reached a RN vs RN position. Igel captured one passer, but Ethereal added another on the king side. Eventually Igel lost its knight for a passer and the game ended in a tablebase win.

game 73, Igel - RubiChess: The game reached a QRB vs QRN position on move 40. Evals were over 1 for a long time, Igel created a passer in the center but it was blocked. For a while Igel was a pawn up and evals increased to around 2, then RubiChess captured the white passer and evals came back down a little. The engines started to shuffle on move 73, evals slowly increased as RubiChess tried to protect its isolated pawns. On move 113 finally Igel captured a pawn, this created an unstoppable passer and a win.

game 79, Ethereal - Nemorino: The engines castled in opposite directions, evals increased steadily without almost any exchanges. Nemorino was two pawns up when it gave a rook for a bishop, the game reached a RRN vs RBN position. Ethereal captured the black pawns until they were all gone, and reduced to a winning R vs B ending 5 pawns up.

game 80, Igel - SlowChess: Igel had an eval of 1 from the start, it was a pawn down but SlowChess did not castle and there were two pairs of black doubled pawns in the center. Evals slowly increased, Igel regained the pawn and SlowChess had little room to move. SlowChess gave a bishop and opened files on the king side, Igel created a passer on the queen side. SlowChess gave more material, it captured the passer and the black queen moved forward and threatened the exposed white king. Igel made sure to avoid a perpetual check, the material advantage was huge and mate was just a matter of time.

Standings after RR3: Igel +6, Ethereal +5, RubiChess +2, SlowChess -1, Pedone -2, Nemorino Xiphos -3, rofChade -4. Ethereal joins Igel at the top with a +4 score including a win against Igel. Igel also lost to rofChade. Only RubiChess is close to the leaders. The bottom is more crowded, Pedone dropped with a -3 score, Nemorino scored -2. rofChade imroved its survival chances with a 0 score.

game 88, Nemorino - SlowChess: SlowChess was up a pawn from the start, the engines reduced to a rook ending. SlowChess captured all the white pawns, the win was just a matter of time.

game 89, Nemorino - RubiChess: Nemorino went a pawn up early, evals increased as the engines exchanged pieces. Nemorino traded a rook for a knight and two pawns, then reduced to a RN vs RR position. Nemorino had passers on both sides and RubiChess could not stop them all, game over. There were two white wins in this opening.

game 92, Ethereal - Pedone: Ethereal had an eval advantage from the start that increased steadily. The black king moved without castling and the black queen was far on the queen side, Ethereal gathered forces and pressed on the king side.  Ethereal used its pawns to expose the black king, a series of exchanges left a BN vs N position and Ethereal had enough pawns to win. A double win for Ethereal in this opening.

game 93, RubiChess - Ethereal: RubiChess had an eval advantage from the start, it placed a knight on e5 in a closed position and evals increased slowly. Ethereal played waiting moves while RubiChess prepared, it started the attack with a knight sacrifice and a rook on the back rank. Ethereal gave the material back to save its king, after a series of exchanges only RN vs RB remained with white a pawn up. RubiChess captured two more pawns and reduced to a winning rook ending. There were two white wins in this opening. 

game 96, rofChade - Nemorino: The engines castled in opposite directions, rofChade pushed pawns on the king side and one pawn reached h6. Nemorino sacrificed a knight for two pawns to free a trapped bishop, but it did not have enough compensation for the piece. The engines exchanged pieces until only RB vs R remained and rofChade captured two pawns. Nemorino reduced to a king and pawns ending which was a win for white.

game 99, SlowChess - Pedone: The black king was forced to move without castling, Pedone wasted time getting its king to safety. SlowChess attacked from the queen side, went a pawn up and reduced to a B vs N ending. It captured two more pawns and the win was a matter of time.

Standings with 3 rounds to go: Igel +7, Ethereal +5, RubiChess +2, SlowChess +1, rofChade -3, Pedone Nemorino Xiphos -4. The top is more or less settled, unless there are last minute surprises. The survival race at the bottom is very close with 4 engines within 0.5 point. Pedone and Nemorino continue to drop, while rofChade is 0.5 points ahead of the rest after beating Nemorino.

game 103, Pedone - Nemorino: Pedone kept its king uncastled, it opened the king side and attacked the black king. Nemorino tried to block with its pieces, Pedone was a pawn up and evals increased slowly. Nemorino gave a rook for a bishop, then the engines reduced to a R vs N ending. Pedone captured black pawns until they were all gone to win.

game 104, Xiphos - rofChade: Xiphos grabbed an early pawn with its queen. Evals slowly increased as the engines exchanged pieces until only RN vs RN were left. Xiphos created connected passers on the queen side, rofChade could not stop their advance. Xiphos queened a pawn and mated.

After round 26 the race at the top is over, Ethereal beat SlowChess and RubiChess drew against Igel. Two head to head games at the bottom, Pedone and Xiphos won while Nemorino and rofChade lost. Standings at the bottom: Pedone Xiphos -3, rofChade -4, Nemorino -5.

game 106, rofChade - Pedone: Evals increased quickly after the start. There were no exchanges, the black pieces were pushed back, Pedone didn't castle and it had very little room to move. rofChade opened a file on the king side, it captured a bishop while the black king ran to the queen side. rofChade's attack continued and it gained material quickly. It was two pieces and 3 pawns up, mate came not long afterwards.

game 107, Nemorino - Ethereal: Evals increased after the start though there were almost no exchanges and material was equal. Nemorino had a space advantage and the black king did not castle. On move 40 Nemorino opened the queen side and then went a pawn up. Ethereal gave another pawn and tried to free its king side rook without success. Ethereal opened the position by giving two more pawns, then it lost its rook for a passer. The game ended in a tablebase win. There were two white wins in this opening.

Standing after round 27: Xiphos rofChade -3, Pedone Nemorino -4. The last round will determine which engines will survive and which will be relegated.

game 110, Igel - Nemorino: Evals increased from the start, Nemorino gave a knight for two pawns and tried to build a wall across the board to prevent attacks. After some shuffling and preparations Igel pushed pawns on the king side and opened a way through the wall. Nemorino had to give its queen to save its king, Igel's material advantage in a QR vs RB position was enough to win.

With this loss Nemorino is relegated.

game 111, Ethereal - rofChade: rofChade gave a pawn early but did not get enough compensation for it and evals increased. The engines exchanged pieces, in a QR vs QR position Ethereal captured a second pawn and then exchanged queens. A rook on the 7th rank and advancing passers gave Ethereal the win.

game 112, Pedone - Xiphos: Pedone outplayed Xiphos in a QB vs RRN position. It threatened the exposed black king and Xiphos had to play defensively. In the end Xiphos had to give material to avoid losing, reducing to a winning Q vs R ending.

The final standings at the bottom: Pedone -3, Xiphos rofChade -4, Nemorino -5. The last game determined the final result at the bottom of the table, Pedone is safe while Xiphos survives with a head to head tiebreak against rofChade.

Season 21 league 2 statistics

A summary statistics table of previous stages and seasons.  

Draw rate, wins

Final draw rate was 56.8%. 

Game termination

The three most common game termination causes were:

42.4% - SyzygyTB
26.5% - TCEC draw rule
18.2% - Mate

There were no crashes in the stage.

Moves per game

Median= 62.8
Average= 65.3

There were 13 games longer than 100 moves, the longest was 156 moves (Arasan - ClassicAra, game 33, draw). 

Time per game (hours)

Median= 1:06
Average= 1:04

Openings

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

The engines had a little freedom to choose the opening variant, 97% of the game pairs repeated the same ECO code and 93.9% repeated the opening variant twice. There was one game pair that didn't repeat the first letter of the ECO code.

Reverse pairs, wins

Reverse pairs, same moves

Pairs of reverse games diverged very quickly, only 22.7% diverged immediately out of book, but 66.7% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 11 plys (Defenchess - Booot, games 61 and 127, KGA, Muzio gambit, two black wins)     

Season 21 league 1 after RR2

Standings after RR2

Igel has a promising lead after RR2, 2 points ahead of its nearest rivals. A group of 3 engines is currently tied for 2nd place.

Currently rofChade and Xiphos are at the bottom, Nemorino and SlowChess are also in danger of relegation. 

Only Igel is unbeaten so far, all other engines have at least one win and one loss. A lot more can still happen, there are 14 more rounds to play.

The openings for league 1 were created by Bastiaan Braams. They are biased, but not extremely so. So far there has been only one opening with wins for both engines, and the draw rate is more than 65%. In season 20 the openings in league 1, also by Bastiaan Braams, were so biased that the expected result was a white win and standings were determined by the number of draws playing black.

Interesting games

game 2, Ethereal - Xiphos: Ethereal had an eval advantage from the start, its eval was over 1 for a long while with only a few pawn exchanges. On move 31 the engines started to exchange pieces and the game reached a RB vs BN position, Ethereal's eval was close to 4. After 30 more moves the game ended in a tablebase win.

game 6, rofChade - SlowChess: SlowChess gave a pawn early, but did not get enough compensation for it. It gave a second pawn and tried to attack the white king, rofChade exchanged pieces and was never in real danger. The game reached a BN vs R position, rofChade had an advanced passer and SlowChess was forced to give a rook for a knight to stop it. rofChade was left with enough material to win.

game 10, Igel - Pedone: The game reached an opposite color bishop ending with Igel two pawns up. Pedone blundered after a long shuffle, allowing Igel to capture two more pawns and win.

game 11, SlowChess - Xiphos: SlowChess had a bishop pair advantage, the game reached a RBB vs RNN position. The bishops were strong in the open board, SlowChess went two pawns up before trading a bishop for a knight. Xiphos had to give its rook to stop a white passer, game over.

game 15, Pedone - SlowChess: SlowChess traded a knight for two pawns at the start, then captured a 3rd pawn. Pedone captured a pawn and created a passer, evals started to climb. The engines reduced to a RN vs R position, Pedone captured pawns and pushed its passer forward. SlowChess captured the passer but Pedone had enough pawns to win.

game 17, Igel - RubiChess: The center and queen side were blocked, the engines mostly shuffled for 30 moves with a few piece exchanges. On move 66 Igel opened a file in the center and traded a knight for a rook. It then gave the material back to create an advanced passer in the center. RubiChess was up a pawn in a QR vs QR position, but when Igel connected a second passer the threat became too great. RubiChess lost material to stop the passers and got mated.

game 26, Nemorino - Igel: Igel was a pawn up with a queen side passer and evals were around 2. After playing out long PV agreements evals came down and the game reduced to a QRB vs QRN position. Nemorino managed to remove the advancing black passer and exchange queens, leading to a drawn tablebase position.

Standings after 7 rounds: Igel +3, Ethereal Pedone +2 Nemorino +1, RubiChess 0, SlowChess -1, Xiphos -3, rofChade -4.

game 29, RubiChess - Pedone: Pedone went a pawn up but its king was uncastled in the center and its DS bishop was trapped and undeveloped. RubiChess placed a knight on d5 and opened the queen side. By the time Pedone freed its bishop RubiChess was a pawn up with a central passer. Pedone lost material fast and was mated.

game 30, Xiphos - Ethereal: After a series of exchanges Xiphos was a pawn up, all the pawns on the queen side were cleared besides one white passer.The engines shuffled for a while, then Ethereal exchanged minor pieces and evals jumped. Only QRR vs QRR remained, Xiphos slowly pushed the passer forward and Ethereal couldn't stop it. Xiphos captured all the black pawns and queened to win. There were two white wins in this opening.

game 42, Nemorino - Xiphos: Nemorino had an eval advantage from the start, the center was blocked and the black king was uncastled in the center. After some shuffling and minor pieces exchanges Nemorino opened the king side and both engines had passers. Evals came down and then became negative as both passers were captured and only QRN vs QRN remained. The white king was in the corner on the queen side, Xiphos threatened the back ranks with its major pieces and it went two pawns up. It took some time but the material advantage was enough for Xiphos to reach a wining knight ending. 

game 44, Igel - Ethereal: Igel went up a pawn after the start, Ethereal traded both its bishops for knights and captured a pawn back. Igel pushed pawns on the king side and drove the black pieces back. After exchanging queens the white bishops found strong outposts that restricted the black pieces. Igel attacked through the queen side and reduced to a B vs N ending with a pawn up. The black knight was trapped in the corner and Ethereal was in zugzwang. Igel was able to queen a pawn and win.

game 51, Nemorino - Ethereal: Nemorino had an eval around 1 from the start, the position was closed and there were only a few exchanges. After a long shuffle Ethereal gave a pawn to open the center and created a passer on the 3rd rank. Evals became negative and climbed quickly, the engines reduced to a QBN vs QNN position. The white king was under threat on the back rank and Nemorino gave a knight to remove the passer. After exchanging queens Ethereal went a pawn up in a B vs NN position. It created an unstoppable passer that ensured the win.

game 54, Igel - Nemorino: The game reached a R vs RN position, with 3 white pawns and 2 black pawns. (Negative) evals were high and it appears that Nemorino could have won. However it played the wrong move and evals dropped to 0. Igel found a way to get rid of the black pawns and Nemorino didn't have the material to win.

Season 21 league 2

Final standings

Pedone and Nemorino advance to league 1. The race at the top of the table was close in the first RR, the first 8 engines were within 1 point of each other. Pedone took the lead with a remarkable +7 score in the 2nd RR, including wins against some of its close competitors. The second qualifying spot was only decided in the last rounds, Nemorino was the only engine that managed to win a game and get ahead of the rest.

Winter, ClassicAra, Seer and Arasan are relegated to league 3. The bottom 3 engines accumulated losses from the start and it was clear they were going to be relegated. Halogen, Vajolet and Winter fought for survival and were close until the end. Winter was tied with Pedone after the first RR, but it dropped down after a poor -4 score in the second RR. In the end Winter's losses to both Halogen and Vajolet sealed its fate.  

The openings for league 2 were by Eduardo Sauceda. They were quite biased with one side starting with a pawn or even a minor piece advantage, including 18 versions of the King's Gambit. Despite this only 6/66 openings resulted in two wins, one for each engine. 

Booot and ClassicAra did not advance further, both started this season in the qualification league. Of the 4 engines that advanced from league 3 only Classic Ara is relegated back. Booot, Minic and Halogen get to stay in league 2.

Pedone and Nemorino will play in league 1 together with:
relegated from premier league in season 20 - Ethereal, rofChade
played in league 1 in season 20: Igel, Slowchess, RubiChess, Xiphos

Interesting games

game 4, Vajolet - Nemorino: Nemorino was a pawn up with a doubled passer, it may have missed a win when it captured another pawn and let Vajolet reduce to a BN vs BN position. Vajolet blocked the passers with its knight and Nemorino could only shuffle. Eventually Nemorino reduced to a drawn opposite color bishop ending.

game 5, Minic - Seer: Seer had an advantage from the opening but Minic managed to equalize. The white king walked to safety on the queen side, then Minic went a pawn up and created passers on the queen side. The game reached a QB vs QN position, Seer promoted a passer first and Minic gave its bishop to eliminate it. Minic was 3 pawns up, it slowly pushed its passers forward. Seer perhaps could have played better but after 30 moves it lost its knight for two pawns, and the queen ending was a win for white.

game 7, Booot - ClassicAra: ClassicAra chose a Q vs RB imbalance, Booot chased the black king all the way to the 1st rank. ClassicAra failed to build a fortress with its pieces, it started losing material and was mated in the end.

game 11, Arasan - Pedone: Arasan was up a rook for a bishop from the start, but its king was vulnerable in the center. Pedone attacked the king and managed to place a rook on the 2nd rank with an advanced central passer. Arasan reduced to a RR vs QB position but couldn't escape the mating net. 

game 14, Pedone - Halogen: Pedone sacrificed a knight early, its compensation was a significant development advantage, the queen was the only active black piece. However Pedone was too passive, Halogen managed to open the position and exchange pieces. Pedone pushed a passer to the 7th rank but there it was stopped, Halogen's extra piece became decisive. Halogen pushed pawns forward, it started to gain more material and won.

game 16, Minic - Fritz: The game reached a double rook ending, Fritz had passers on the queen side and Minic had a passer on the king side. Fritz chose to move its king to the queen side and this turned out to be a mistake. The white rooks captured two black passers, while Minic traded its king side passer for a rook and won. 

game 17, Defenchess - Nemorino: Nemorino had an advantage in a BN vs BB position, somehow Defenchess found a way to block a pair of black passers while keeping the black king away, while a white passer had to be watched by the bishops. Nemorino could only shuffle, eventually Defenchess gave its knight to take out the black passers and the game ended in a tablebase draw.

game 23, Halogen - Vajolet: Vajolet was a pawn up from the start. The game reached a QRB vs QRN position, Vajolet captured another pawn, exchanged queens and created a passer. The black king came forward, Halogen captured the passer but Vajolet reduced to a winning king and pawns ending.

game 29, ClassicAra - Fritz: Fritz was up a pawn from the start. ClassicAra sacrificed a knight, perhaps it thought it could attack the black king in the center. Instead Fritz attacked and forced ClassicAra to give more material. Fritz chased the white king to a mating net in the center of the board.

game 31, Booot - Nemorino: Nemorino was a pawn up in a BN vs BN position, with 3 connected passers on the king side. The game ended in an unusual opposite color bishop ending, black two pawns up, which was a tablebase win.

game 34, Halogen - Defenchess: Defenchess was a pawn up with a passer on the king side. It gave 3 pawns to open up the position and push the passer to the 2nd rank. The white king was exposed to attack and Halogen started to lose material. Defenchess captured a bishop for the passer, it continued to gain material and mate was unavoidable.

game 36, Pedone - Vajolet: Vajolet was two pawns up from the start, with the white king hiding behind a black pawn. Pedone gave a rook for a knight and captured the black pawn on the 2nd rank, while pushing a passer to the 7th rank. In a QRB vs QRR position Pedone seemed to blunder, allowing Vajolet to reduce to a winning B vs R ending. 

game 42, Nemorino - Fritz: Fritz was a pawn up from the start, Nemorino had an advanced passer in the center. The engines exchanged most pieces, Fritz captured the white passer and reduced to a rook ending with connected passers in the center. Nemorino managed to stop the passers but it was 3 pawns down by then and couldn't hold.

game 44, Arasan - Nemorino: Nemorino converted an unusual BNN vs Q imbalance.

game 50, Defenchess - Vajolet: Defenchess was better in the middlegame, it reduced to a rook ending with a pawn up. It then created a passer and pushed it forward to win.

game 56, Halogen - Fritz: Fritz was up a pawn in a RRN vs RRB position, with a pawn majority on the queen side. Halogen managed to capture a pawn and equalize on the queen side, Fritz cleared the white pawns on the king side and went 2 pawns up to win. 

game 57, Winter - Nemorino: The game reached a R vs N ending with Nemorino 3 pawns up. Winter couldn't block the advancing black pawns.

game 59, Vajolet - ClassicAra: ClassicAra gave a knight for two pawns to create a passer and a pawn majority on the queen side. Vajolet gave a knight to remove two pawns, the game reduced to a QR vs QR position with black a pawn up with a passer. After exchanging queens ClassicAra captured more pawns and the rook ending was a win. 

game 60, Minic - Defenchess: (Negative) evals increased steadily from the start. The game reached a QRB vs QRN position, the white pawns were weak on the queen side. Defenchess went two pawns up and created a passer, after 20 moves of slow improvement Defenchess connected a second passer. Minic tried to attack the black king and lost material, game over.

game 61, Defenchess - Booot: Defenchess was down a knight from the start. It captured two pawns and chased the exposed white king, but the position stabilized and Booot still had a piece advantage. The engines exchanged pieces slowly until only R vs RB were left. Booot gradually captured the white pawns, after exchanging rooks the game ended in a tablebase win.

game 65, Fritz - Winter: Winter was up a pawn after the start and (negative) evals steadily increased. The game reached a RRB vs RRB position, Fritz equalized material but its pawns were weak and its rooks played defensively. After exchanging a pair of rooks Winter went two pawns up, then it used its passers to gain material and win.

Standings after 11 rounds: Nemorino +3, Fritz Defenchess Minic +2, Pedone Booot Vajolet Winter +1, Halogen -1, Arasan ClassicAra -3, Seer -6. Eight engines are in the race for 2 qualification spots. The bottom 4 engines seem to be heading for relegation, perhaps Halogen still has a chance of surviving. Keep in mind that some of the openings were very biased, and the ranking may change when the reverse games are played.

game 68, Arasan - Winter: Winter grabbed a pawn in a RB vs Q position, this allowed Arasan to push a passer and force a perpetual check draw.

game 69, Fritz - Pedone: (Negative) evals increased from the start. Pedone went a pawn up and then a series of exchanges left only QR vs QR. Pedone captured a second pawn, Fritz had a passer on the 7th rank as a counter. After exchanging queens Pedone captured the passer and the rook ending was a win.

game 70, Nemorino - Vajolet: The game reached a 7-man queen ending which was a cursed win for black, that needs more than 50 moves without captures or pawn moves in optimal play. Vajolet eventually gave up, both engines lowered their evals and the game was adjudicated.

game 76, Vajolet - Fritz: The white DSB was trapped on the queen side, Fritz offered a knight for the trapped bishop and created an advanced passer. Vajolet managed to capture the passer but then Fritz created another, this time it was unstoppable. Fritz promoted to a queen and soon mated.

game 78, Winter - Halogen: The game reached a QR vs QR position with Halogen a pawn up. After exchanging queens Winter perhaps may have held, but after clearing the king side pawns the black king was better placed. Halogen drove the white rook away and captured a second pawn to win.

game 79, Booot - Winter: Winter was up a knight from the start, and this became a R vs BN imbalance. Booot created connected passers on the king side, it moved its rooks forward while most black pieces were stuck on the queen side. Winter captured one passer but the other reached the 7th rank. Winter had no effective counter, Booot gained material and won.

game 82, Fritz - Minic: Minic was up a pawn from the start. The white queen was active on the queen side, and when Minic shifted its pieces to the king side Fritz grabbed a pawn. However Minic reduced to a RN vs RB position and again went a pawn up. After exchanging rooks Minic created a queen side passer and Fritz gave its knight to stop it, leading to a tablebase win. A double win for Minic in this opening.

game 83, Nemorino - Defenchess: Nemorino grabbed a pawn and Defenchess trapped its rook, Nemorino traded the rook for a bishop. The game reached a RBN vs RRB position. Nemorino had 2 passers, after exchanging minor pieces Defenchess captured one passer. Both engines had one advanced passer but were unable to promote, after exchanging a pair of rooks Defenchess captured the white passer and won with its own.

game 87, Defenchess - Fritz: The game reached a QRN vs QRB position, Fritz with a passer in the center. For 25 moves Defenchess blocked the passer on the 3rd rank, Fritz went a pawn up and then pushed the passer once and exchanged rooks. Defenchess gave its knight to capture the passer, Fritz used the exposed white king to gain more material and win.

game 89, Vajolet - Halogen: Vajolet blundered in a seemingly drawn RB vs RN position, Allowing Halogen to exchange rooks and clear a path for an advanced passer on the queen side. By the time Vajolet captured the passer Halogen took over the rest of the board, it went two pawns up and won. A double white win in this opening.

game 92, Winter - Vajolet: Vajolet created a passer in the center, Winter countered with a passer on the 7th rank and threats on the back rank. Winter gave material to keep an attack going, Vajolet was able to defend. In the end both passers were gone and Vajolet was a rook up, game over.

Standings with 6 rounds to go: Pedone Minic Defenchess +4, Nemorino Booot +3, Fritz +2, Halogen Vajolet 0, Winter -2, ClassicAra -5, Arasan -6, Seer -7. There are still 6 engines in the qualification race. Pedone joined the leaders with 3 wins. Minic, Defenchess and Booot also improved with a +2 score. Halogen improved its chances of survival after it beat Winter and Vajolet, Winter is now in 9th place after losing to Vajolet as well.

game 102, Vajolet - Pedone: The game reached a RBN vs RBN position with black a pawn up and 3 connected passers on the king side. After exchanging bishops Pedone blocked Vajolet's attempt to push passers, then started to capture white pawns. Pedone was 3 pawns up after it cleared the white queen side pawns, the win was just a matter of time. Two black wins in this opening.

game 104, Pedone - Minic: Minic was two pawns up but its king side rook was trapped. Pedone increased the pressure on the black king and Minic did not have enough pieces to defend. Minic gave material but only postponed the mate.

game 105, Winter - Defenchess: Defenchess was three pawns up but it was behind in development and its king was uncastled in the center. Winter sacrificed two rooks for a knight and attacked, the black king had to run while the black pieces were unable to help. Defenchess lost a queen and bishop and Winter pushed a passer to the 7th rank. Winter continued to gain material until it mated.

game 108, Fritz - Nemorino: The game reduced to a QRR vs QRR position. Nemorino had a pawn majority on the queen side, it went a pawn up and reduced to a rook ending. Fritz moved its rook to the queen side and Nemorino captured a second pawn on the king side. Evetually Fritz lost its rook for a passer, game over. Two black wins in this opening. 

game 113, Defenchess - Pedone: Pedone was up a knight for two pawns from the start. The engines exchanged pieces until only rooks and knights remained, after a while Pedone reduced to a R vs RN position. Pedone captured black pawns patiently, making sure it kept a few pawns of its own alive. Eventally Pedone created an unstoppable passer and used it to win.

Standings with 3 rounds to go: Pedone +7, Nemorino +4, Minic Booot +3, Defenchess Fritz +2, Halogen 0, Vajolet Winter -1, ClassicAra -4, Seer -7, Arasan -8. Pedone almost surely ensured a qualification spot after 3 straight wins, beating both Minic and Defenchess. The second qualification spot and the 4th relegation spot are still wide open.

In round 20 only Fritz was able to win a game against Arasan, now at +3 half a point away from Nemorino in 2nd place.

game 123, Nemorino - Winter: Winter was up a pawn from the start but Nemorino managed to equalize. Nemorino captured two pawns using an attack on the black king, then reduced to a RRN vs RRN position and created connected passers on the queen side. Winter trapped and captured a knight but had to give back the piece to capture a passer. Nemorino still had a second passer in a double rook ending, enough to win. A double win for Nemorino in this opening.

In round 21 Booot, Nemorino and Pedone won, while Winter lost. Race for 2nd place: Nemorino +5, Booot +4, Minic Fritz +3. Race for 9th place: Halogen 0, Vajolet -1, Winter -2.

game 127, Booot - Defenchess: Booot was down a knight from the start, it was two pawns up and had a passer in the center. The engines exchanged pieces until only B vs BN remained. It took Defenchess more than 20 moves to capture all the white pawns, the game ended in a tablebase win. Two black wins in this opening.

game 131, Winter - Fritz: Fritz was up  a pawn from the start. It opened the king side and in a series of exchanges won a rook and two pawns for a bishop. The white king was exposed, Winter lost more material and was soon mated. Two black wins in this opening.

Booot lost in the last round, and once Nemorino drew its game it guaranteed 2nd place. Winter lost against Fritz and it is the 4th relegated engine.

Season 21 league 3

Final standings

Minic, Booot, Halogen and ClassicAra advance to league 2. Minic and Booot led the league from the start, Minic was better in the second RR and it won by a small margin. Halogen had a poor first RR, it joined the leaders in the second RR with a +3 score. Many engines were in reach of the last qualification spot, in the end it was down to ClassicAra and Wasp. Wasp lost to Booot in the round before last and ClassicAra qualified in the end.

Marvin, Pirarucu, Topple and Weiss are relegated to league 4. Pirarucu, Topple and Weiss lost many games with almost no wins, they were at the bottom of the table from the start and headed for relegation. Interestingly, Weiss beat Combusken twice, causing Combusken to be involved in the race against relegation when it could have been closer to the top otherwise. Marvin was a part of the middle group of engines, it dropped to 9th place after a loss to Wasp in round 20 and couldn't escape relegation.

The draw rate was high in league 2, around 70%. As a result it took time for the score distribution width to increase. The engines in the middle of the table were close to one another, only 2 points separate 3rd and 9th place in the final standings. Luck/chance was an important factor considering that only one DRR was played.

Booot and ClassicAra continue their journey to the higher leagues, both started in qualification. Halogen started in league 4 and this is its second qualification in season 21. On the other hand, Koivisto's journey has ended in league 3 after starting in qualification.

The 4 qualifiers will play in league 2 together with :
Relegated from season 20 league 1: Nemorino, Defenchess
Played in season 20 league 2: Vajolet, Pedone, Winter, Fritz, Arasan, Seer

Interesting games

game 16, Weiss - Halogen: Weiss blundered in a drawn B vs N ending, after the game was close to being adjudicated by the draw rule. Halogen used a zugzwang to force a pawn move, then went two pawns up and won.

game 21, Halogen - Topple: The game started with a King's gambit opening, the queens were off early and Topple captured a rook for a knight and pawn. Halogen played better and it seemed to be winning with a passer advancing on the king side. The passer reached the 7th rank but Halogen didn't find the right moves and evals came down. Topple managed to clear the queen side pawns and the game ended in a drawn RBN vs RRB position.

game 24, Wasp - Tucano: Tucano blundered in the opening, Wasp gave a bishop and attacked the uncastled black king. The game reached a QRR vs QRR position with white two pawns up. Wasp continued to attack the vulnerable black king, it gained more material and won.

game 27, Weiss - Minic: Weiss sacrificed a knight for pawns and then avoided a repetition draw. Minic exchanged pieces, blocked the white passers and reduced to a winning R vs RB position.

game 30, Marvin - Booot: Marvin gave two knights for a rook and two pawns. Booot managed to trap a rook and capture it for a bishop, with only RB vs RBN left. In a slow endgame Booot captured all the white pawns to win.

game 36, Tucano - Combusken: Tucano had a promising eval advantage, but it chose to reduce to a Q vs RN ending and evals slowly came down. The game continued for 30 more moves and ended in a tablebase draw.

game 37, Combusken - ClassicAra: Combusken played a RBN vs RR ending better, it managed to block and capture all the black pawns while pushing a passer to the 7th rank. ClassicAra crashed a few moves before losing.

game 43, ClassicAra - Halogen: The game reached a B vs N ending. The white pieces were better placed, ClassicAra captured a pawn and created a passer. Then ClassicAra captured another pawn and secured the win.

game 48, Combusken - Weiss: After a long shuffle Weiss shifted its pieces to the king side and (negative) evals started to increase. Combusken gave a rook for a knight while Weiss created a passer on the king side, the game reached a QRN vs QRR position. The black pieces were strong in the open files, Weiss exchanged queens and then started to capture pawns. Combusken gave its rook for the passer, game over.

game 66, Koivisto - Minic: There was only one minor piece exchange in the first 30 moves. Minic had a bishop on d2 and Koivisto could not get rid of it. Minic opened a file in the center and Koivisto's defense collapsed. Minic captured a bishop, then attacked the white king and mate followed.

Standings after 11 rounds: Booot +4, Minic +3, ClassicAra Wasp +2, Koivisto Combusken +1, Marvin Halogen 0, Tucano -1, Weiss -3, Pirarucu -4, Topple -5. The draw rate is high and the engines are still close together, especially in the middle of the table. The top two and bottom three engines are likely to stay where they are, but a lot can still change in RR2.

game 75, Weiss - Booot: Weiss was a pawn up in a QRB vs QRN position, with conneted passers on the queen side. Then it allowed Booot to sacrifice a rook and force a perpetual check draw.

game 78, Wasp - Minic: Minic opened the a file and started attacking the white back ranks, with (negative) evals increasing. Minic played patiently, it captured a pawn on move 64, then reduced to a same color bishops ending on move 81. Minic captured a second pawn and pushed its passers to win.

game 82, Halogen - Weiss: Evals increased from the start, Halogen went a pawn up and then reduced to a RB vs RN position. It took another 40 moves to mate but there was never any doubt about the outcome.

game 92, Wasp - Combusken: Combusken was better in a RN vs RR position, but it grabbed a pawn and let Wasp push a passer forward. This created a threat on the black king, Combusken was forced to reduce to a drawn rook ending.

Standings with 6 rounds to go: Minic +6, Booot +5, Halogen ClassicAra +2, Wasp Koivisto Combusken +1, Marvin 0, Tucano -2, Weiss Pirarucu -5, Topple -6. Minic and Booot extend their lead and are likely to advance. At least 5 engines are in the race for the remaining 2 qualification spots, Halogen improved its chances with two wins. The bottom of the table is clearer, only one relegation spot is still in question.

game 99, Pirarucu - Koivisto: The engines shuffled for a long while, then reduced to a BB vs BN position. Pirarucu used its bishop pair to trap the black king in the corner, the white king was active in the center and Pirarucu went a pawn up. Koivisto then lost a second pawn and the game was over.

game 103, ClassicAra - Combusken: ClassicAra had the advantage in a RB vs RN position, a pawn up and with a passer on the 7th rank. However it let the advantage slip and Combusken captured the passer. Eventually both engines queened a pawn and the game ended in a tablebase draw.

game 109, Halogen - ClassicAra: ClassicAra gave a knight for a pawn early, it tried to attack the white king but Halogen was able to defend. ClassicAra gave more material in desperation, when it couldn't give checks anymore Halogen mated.

game 114, Weiss - Combusken: The game reached a QR vs QR position, Combusken was a pawn up with a doubled passer on the king side but its king was more vulnerable. Combusken played inaccurately, Weiss captured a pawn and created a passer, then eliminated the black king side pawns for a decisive advantage. The game ended in a tablebase win.

Standings with 3 rounds to go: Minic +7, Booot +5, Halogen +3, ClassicAra Wasp +1, Combusken Koivisto Marvin Tucano 0, Pirarucu Weiss -5, Topple -7. Halogen has a 1 point margin in 3rd position, with a good chance of qualifying after its win against ClassicAra. Tucano improves its survival chances with two wins. There is a tight group of 6 engines in the middle of the table, of which one will qualify and one will be relegated.

game 117, Tucano - Pirarucu: Tucano was winning in a QB vs QR position with a passer on the 6th rank. Pirarucu traded B for R and Tucano took with a pawn instead of its queen, giving Pirarucu a passer. This was a strong enough counter to force a draw in a queen ending.

game 118, Wasp - Marvin: Evals increased gradually with almost no exchanges, Marvin had little room to move. On move 43 Wasp went a pawn up and created a passer on the queen side, with evals over 3. It managed to push the passer to the 7th rank. Marvin was busy defending, Wasp captured another pawn and created a second passer on the king side. Eventually Wasp promoted a pawn to a queen and mated.

In round 20 ClassicAra and Wasp won, most likely one of them will qualify. Marvin lost and is now in sole 9th place. Tucano missed a win against Pirarucu. Standings with 2 rounds to go: ClassicAra Wasp +2, Combusken Koivisto Tucano 0, Marvin -1.

game 123, Booot - Wasp: The game reached a BN vs R ending, Booot moved its king forward and Wasp was outnumbered. Booot went a pawn up and slowly pushed a passer until it promoted to a queen.

In round 21 Wasp lost and is now in 5th place, 0.5 points behind ClassicAra. No change at the bottom of the table, Marvin is still in 9th place. Standings before the last round: ClassicAra +2, Wasp +1, Combusken Koivisto Tucano 0, Marvin -1.

All 6 games were drawn in the last round, ClassicAra qualifies and Marvin is relegated.

Season 21 league 3 statistics

A summary statistics table of previous stages and seasons.   

Draw rate, wins

Final draw rate was 72.0%.

Game termination

The three most common game termination causes were:

43.2% - TCEC draw rule
30.3% - SyzygyTB
13.6% - Mate

There was one crash in the stage, ClassicAra crashed a few moves before losing.

Moves per game

Median= 59
Average= 66.2

There were 14 games longer than 100 moves, the longest was 183 moves (ClassicAra - Combusken, game 103, draw). 

Time per game (hours)

Median= 1:02
Average= 1:02

Openings

There were 4-move book openings in this stage chosen by Cato. The first letter of the ECO codes was distributed as follows:

The engines had some freedom to choose the opening variant, 90.9% of the game pairs repeated the same ECO code twice, and 81.8% repeated the same opening variant. Only in two (3.0%) game pairs the ECO first letter was not repeated twice.

Reverse pairs, wins

Reverse pairs, same moves  

Pairs of reverse games diverged very quickly, 34.8% diverged immediately out of book, 66.7% of the pairs diverged at most after 1 move. The longest repeated sequence of moves was 11 plys (Wasp - Tucano, games 24 and 90, English Mikenas-Carls, Flohr variation, Wasp won as white)