Epoch AI published Mystery Game Puzzles, a benchmark of 100 mid-game positions from a puzzle-oriented variant of an undisclosed well-known game, in which models must select the single best next move. The setup mirrors Epoch's existing Chess Puzzles benchmark, but the game's identity is withheld to reduce the risk of benchmark-specific preparation by model developers. Puzzles were generated programmatically by sampling random games, rolling forward to mid-game states, and filtering to states with a single best move. Models receive the state as text in a minimal agent scaffold and submit a move through a tool; submissions are normalized to the game's standard notation, illegal moves are marked incorrect, and unextractable responses are recorded as unanswered. Epoch is not publishing the prompt, example positions, or model transcripts.

• epoch.ai2026-08-06