More than one year ago, leading developers of the chess engine Stockfish, Tord Romstad and Stéphane Nicolet, with broad support from the development community, filed suit against ChessBase GmbH before the District Court Munich I (Az. 42 0 9765⁄21) to enforce the GNU General Public License v3 (GPL) license termination provision, claiming repeated violation of the license conditions by ChessBase with their products Fat Fritz 2 and Houdini 6. We are pleased to announce that we have found an agreement (PDF in German and English) that strengthens the Stockfish project in its aim to deliver the world’s number #1 chess engine as Free Software and that allows ChessBase to distribute our software in the future.
Fat Fritz 2 and Houdini 6 are based on Stockfish, and ChessBase infringed on the license by not distributing these products as Free Software in accordance with the GPL. Their customers have not received the necessary information, namely the text of the GPL license covering these programs and the corresponding source code of these programs, to exercise the rights granted by the GPL. These rights include the right to reproduce, modify and distribute GPLed programs royalty-free. This infringement is not without consequences, and in the near future ChessBase will no longer sell products containing Stockfish code, while informing their customers of this fact with an appropriate notice on their web pages. Existing customers can continue to use the software, and, if ChessBase provides a download in a GPL compliant way, download an already purchased copy.
Nevertheless, in one year from now, Tord and Stéphane will reinstate ChessBase’s license. We feel that this is in the spirit of Free Software and to the benefit of the community. ChessBase has now acknowledged the value and potential of open source software, and Stockfish in particular, and made a clear commitment to respecting the Free Software principles. To prevent future violations, ChessBase will create the position of a Free Software Compliance Officer, and will maintain a domain [foss.chessbase.com] that lists their products containing Free and Open Source Software (FOSS). Last but not least, in the future ChessBase will give appropriate credit for the use of Stockfish in their products and neural networks offered by ChessBase for use with Stockfish will be provided under GPL or a compatible license.
Finally, the Stockfish team, unpaid hobbyists that all prefer coding over litigating, did not seek damages or other forms of financial compensation. We would like to thank the community for their essentially unlimited time, advice and financial support that made this possible.
For the Stockfish team,