https://en.wikipedia.org/wiki/Endgame_tablebase

This market resolves yes when a complete 8 man tablebase is finished and released. This tablebase must include every position, not just "nontrivial" positions. In the event something is released but it takes time to verify, this market resolves to the year in which the complete version of the tablebase was accessible by a member of the public. It's okay if the tablebase requires a fee or subscription to access, as long as any member of the public could theoretically access it and it is verified to be complete. It is unlikely that I bet on this market, and if I do I will sell all my shares before resolving the market