Historically, games claiming the record often fall into the range of . One specific type of game that generates these numbers is a Force Repetition .
Many deep theoretical lines are pioneered in Daily (Correspondence) Chess, where players have days to consult databases, pushing the boundaries of what is considered "book." Summary of Theoretical Depth by Opening Common Theoretical Depth Variation with Longest Theory Ruy Lopez 15–25 moves Marshall Attack, Breyer Defense Sicilian Defense 10–25 moves Najdorf Variation Semi-Slav 12–30 moves Botvinnik Variation King's Indian 15–20 moves Mar del Plata Variation Longest "book opening" - Chess Forums longest book move sequence chess.com
Endgame theory starts here. The Berlin Endgame has been analyzed to move by human GMs, but the book on Chess.com usually runs out around move 30 because players deviate early to avoid boring draws. Still, you can find sequences—specifically the 9.h3 line—where moves 1 through 29 are all in the Masters’ database. Historically, games claiming the record often fall into
If you are looking to "stay in book" as long as possible, these openings are notorious for their deep theoretical branches: Ruy Lopez (Zaitsev or Marshall Attack) The Berlin Endgame has been analyzed to move
Crucially, While a supercomputer like Stockfish 16 might see 50 moves ahead, the human book typically runs dry between move 15 and move 25 in most mainstream lines. But there are exceptions.