Games 31-32 started with a 24-ply book sequence, with white a rook up and a knight trapped in the corner, and the black king uncastled after moving. In game 31 Stockfish captured the knight and pushed pawns on the king side facing the white king. Its eval dropped to 0 as it opened the king side, the two black knights gave checks and AllieStein avoided a repetition. To get its king out of trouble AllieStein gave two pawns, Stockfish sacrificed a rook to finish the game in a check repetition.
In game 32 both engines did not castle. AllieStein pushed pawns on the king side and the white king walked to the queen side. After capturing the white knight in the corner AllieStein planned in its PV to capture the pawns on the king side. The plan included a knight sacrifice and allowing Stockfish to push a passer on the queen side. AllieStein went ahead with this and Stockfish played along. The engines' PVs disagreed on move 32, AllieStein made its move with 3 seconds thinking time.
Stockfish's eval jumped over 1.5 and climbed fast. AllieStein bet the game on the value of the three advanced passers in the center. Stockfish's advanced passer together with mate threats and attacks on pieces forced AllieStein to defend. AllieStein only realized it was in trouble on move 39.
After exchanging queens Stockfish captured one of the passers. The threat of the black central pawns was smaller, Stockfish could block them with its bishops. The extra rook was enough for a win, the game was adjudicated a few moves later.
AllieStein started game 33 with an eval under 1. The white king walked to the queen side, AllieStein's eval increased over 2 while Stockfish's eval remained low. AllieStein tried to press on the queen side but nothing came out of it, Stockfish's eval dropped to 0. The queen side pressure was released after several exchanges, Stockfish then gave a rook for a bishop and used a queen and knight combination to threaten the white king. The game reached a QRN vs QBN position and ended in a perpetual check draw. In game 34 Stockfish castled long, its eval went over 1. AllieStein had a bishop pair but in a closed position the two white knights were more useful. The pawn lines stabilized and the engines started to shuffle. Stockfish avoided a 50-move draw and its eval came down. The engines reduced to a N vs B ending and the game ended in a tablebase draw.
The engines castled in opposite directions in game 35. AllieStein's eval increased over 3 as the engines started to exchange pieces, its eval peaked around 4. The game reached a RN vs RB position with white a pawn up. Stockfish's eval came down to 0 and the engines started to shuffle. AllieStein created passers on the queen side and Stockfish had a passer on the king side. Stockfish gave its bishop to stop a white passer, AllieStein gave a rook to stop a black passer, the remaining N vs R ending was a draw. In game 36 AllieStein kept its king uncastled, Stockfish's eval was a little over 1 and did not increase. AllieStein opened the king side and the white king walked back to the center, Stockfish went up a pawn but its eval came down to 0. After a long series of exchanges only RRN vs RRB remained, Stockfish ended the game with a check repetition.
Evals were low from the start of game 37. AllieStein gave two pawns but had a bishop pair, the game reached a RBB vs RNN position on move 22. In the next 35 moves the engines exchanged a pair of pawns, AllieStein captured a black passer and then the engines reduced to a B vs N ending. The game should have ended by the draw rule on move 44, the game eventually ended on move 90. In game 38 Stockfish pushed pawns on the king side and its king became exposed. AllieStein's eval turned negative, it tried to press on the king side but Stockfish kept the files closed. The game reached a rook ending on move 48. Black's extra pawn was not enough, the game was adjudicated 25 moves later.
Games 39-40 started with a 20-ply book sequence in the Frence defense, Boleslavsky variation, where the engines castled in opposite directions. In game 39 AllieStein pushed a pawn to h6, a thorn pawn, its eval over 1.5. Stockfish pushed pawns on the queen side, it was surprised when AllieStein remained passive. Stockfish captured on b2 and the white king hid behind the pawn, AllieStein's eval jumped over 2.5.
AllieStein's eval climbed quickly, the black DS bishop was blocked and the white knight on d6 was a threat for the black pieces. The engines exchanged queens and Stockfish could no longer threaten the white king. Stockfish opened the long diagonal to find space for its bishop and to protect the b2 pawn, the only safe square it found was in the corner.
AllieStein soon captured the two black pawns on the b file. The trapped bishop could not get out of the corner, and the other black bishop on d5 was blocking the white rooks from attacking the back ranks.
AllieStein used its knight to drive the d5 bishop away and the rooks came forward. AllieStein captured a third pawn, the game was adjudicated 10 moves later.
There were many exchanges after the start of game 40, only RRN vs RRB remained on move 27. The pawn lines stabilized and the engines shuffled for a while as evals slowly came down. Stockfish moved both its rooks to the 7th rank and the game ended in a 3-fold repetition.
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