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Official Stockfish pre-release: Stockfish dev-20250804

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Official prerelease Stockfish dev-20250804
Rating Chess Engines Diary CEDR=3763

Great news for chess enthusiasts! The pre-release version of Stockfish dev-20250804, widely recognized as the world's top chess engine, has been released. This brings us one step closer to the next official release. Our team is excited to begin testing it today, and we'll be sure to share the results on our website. Stay tuned!

What changes in the new Stockfish dev-20250804 version?

Only set ep square if ep capture is possible for positions such as:

position fen rr6/2q2p1k/2P1b1pp/bB2P1n1/R2B2PN/p4P1P/P1Q4K/1R6 b - - 2 38 moves f7f5
position fen 8/p2r1pK1/6p1/1kp1P1P1/2p5/2P5/8/4R3 b - - 0 43 moves f7f5
position fen 4k3/4p3/2b3b1/3P1P2/4K3/8/8/8 b - - moves e7e5

ep is not possible for various reasons. Do not set the ep square and the do not change the zobrist key, as if ep were possible.

This fixes 3-fold detection, which could in rare cases be observed as a warning generated by fastchess for PVs that continued beyond an actual 3-fold.

Also fixes wrong evals for certain moves e.g. a2a1 for
position fen 4k3/1b2p2b/8/3P1P2/4K3/8/8/r7 b - - 0 1 moves e7e5 e4e3 a1a2 e3e4 a2a1 e4f3 a1a2 f3e4
fixes https://github.com/official-stockfish/Stockfish/issues/6138

originally written and tested by rn5f107s2, with small buglet as
https://tests.stockfishchess.org/tests/view/685af90843ce022d15794400

failed STC
LLR: -2.93 (-2.94,2.94) <-1.75,0.25>
Total: 130688 W: 33986 L: 34362 D: 62340
Ptnml(0-2): 414, 13292, 38302, 12928, 408
https://tests.stockfishchess.org/tests/view/688bcb35502b34dd5e7111c9

passed LTC
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 99018 W: 25402 L: 25273 D: 48343
Ptnml(0-2): 54, 9097, 31089, 9204, 65
https://tests.stockfishchess.org/tests/view/688c613c502b34dd5e7112d3
https://github.com/official-stockfish/Stockfish/pull/6211

Bench: 2946135
Co-authored-by: Joost VandeVondele



Here are some sample tournament wins for the Stockfish engine on Android and Windows::





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