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Official Stockfish pre-release: Stockfish dev-20250906

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Official prerelease Stockfish dev-20250906
Rating Chess Engines Diary CEDR=3761,4

Great news for chess enthusiasts! 
The pre-release version of Stockfish dev-20250906, 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-20250906 version?

Adjustment of the aspiration window after fail high/low.

For the new bound in the opposite direction of the fail, use a weighted average of alpha, beta and best value +- delta. In the case of a fail high, different average weights are used depending on whether or not there was a best move change during the last search.
The weights are determined from the following two consecutive LTC tunings.

First tuning: https://tests.stockfishchess.org/tests/view/68ab727975da51a345a5ac2e
Second tuning: https://tests.stockfishchess.org/tests/view/68aba3fe75da51a345a5ad52

Passed LTC:
LLR: 2.94 (-2.94,2.94) <0.00,2.00>
Total: 39504 W: 10243 L: 9947 D: 19314
Ptnml(0-2): 25, 4182, 11041, 4480, 24
https://tests.stockfishchess.org/tests/view/68acbb6d6217b8721dca95f8

Passed VLTC:
LLR: 2.95 (-2.94,2.94) <0.50,2.50>
Total: 91196 W: 23574 L: 23167 D: 44455
Ptnml(0-2): 13, 8943, 27276, 9356, 10
https://tests.stockfishchess.org/tests/view/68af64786217b8721dca993d

closes https://github.com/official-stockfish/Stockfish/pull/6292
Bench: 2785713

Stockfish dev-20250906 download (all files: stockfish-windows-armv8.exe, stockfish-windows-armv8-dotprod.exe, stockfish-windows-x86-64.exe, stockfish-windows-x86-64-avx2.exe, stockfish-windows-x86-64-avx512.exe, stockfish-windows-x86-64-avx512icl.exe, stockfish-windows-x86-64-avxvnni.exe, stockfish-windows-x86-64-bmi2.exe, stockfish-windows-x86-64-sse41-popcnt.exe, stockfish-windows-x86-64-vnni256.exe, stockfish-windows-x86-64-vnni512.exe  )

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





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