Stockfish 11

It is our pleasure to release Stockfish 11 to our fans and supporters.

Downloads are freely available at

This version 11 of Stockfish is 50 Elo stronger than the last version, and 150 Elo stronger than the version which famously lost a match to AlphaZero two years ago. This makes Stockfish the strongest chess engine running on your smartphone or normal desktop PC, and we estimate that on a modern four cores CPU, Stockfish 11 could give 1:1000 time odds to the human chess champion having classical time control, and be on par with him. More specific data, including nice cumulative curves for the progression of Stockfish strength over the last seven years, can be found on our progression page, at Stefan Pohl site or at NextChessMove.

In October 2019 Stockfish has regained its crown in the TCEC competition, beating in the superfinal of season 16 an evolution of the neural-network engine Leela that had won the previous season. This clash of style between an alpha-beta and an neural-network engine produced spectacular chess as always, with Stockfish emerging victorious this time.

Compared to Stockfish 10, we have made hundreds of improvements to the codebase, from the evaluation function (improvements in king attacks, middlegame/endgame transitions, and many more) to the search algorithm (some innovative coordination methods for the searching threads, better pruning of unsound tactical lines, etc), and fixed a couple of bugs en passant.

Our testing framework Fishtest has also seen its share of improvements to continue propelling Stockfish forward. Along with a lot of small enhancements, Fishtest has switched to new SPRT bounds to increase the chance of catching Elo gainers, along with a new testing book and the use of pentanomial statistics to be more resource-efficient.

Overall the Stockfish project is an example of open-source at its best, as its buzzing community of programmers sharing ideas and daily reviewing their colleagues' patches proves to be an ideal form to develop innovative ideas for chess programming, while the mathematical accuracy of the testing framework allows us an unparalleled level of quality control for each patch we put in the engine. If you wish, you too can help our ongoing efforts to keep improving it, just get involved :-)

Stockfish is also special in that every chess fan, even if not a programmer, can easily help the team to improve the engine by connecting their PC to Fishtest and let it play some games in the background to test new patches. Individual contributions vary from 1 to 32 cores, but this year Bojun Guo made it a little bit special by plugging a whole data center during the whole year: it was a vertiginous experience to see Fishtest spikes with 17466 cores connected playing 25600 games/minute. Thanks Guo!

The Stockfish team