From a FIDE Online Arena Facebook post (which appears copy/pasted from elsewhere), I'm interested in the part in bold:

(Image of a chess board with two kings and no pawns nor pieces omitted.)

This was the position after 91.Kxb8 in the game NewRival1816 - Faile06 in a computer tournament in 2001. According to the rule, the game should have been stopped as a draw here, but this rule apparently wasn't implemented ... 493 moves is a new world record, ...

I find it hard to believe this is up-to-date, but I didn't immediately find examples to indicate otherwise (e.g. long computer chess games didn't give anything relevant).

Question: Have there been computer-vs-computer chess games exceeding 493 moves?

For this to be meaningful, I insist that both engines were actually playing "good moves", i.e., moves that both engines thought maximized its score. Or in other words, the engines were actually playing chess, and not trying to maximize the length of the game.

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Tim Krabbe discusses this in his website (see section 328).

It's an old post - dating to 2006 - so it's certainly possible. However 2006 was also a long time ago. Since then engines have gotten more familiar with the rules, and all the top engines I'm aware of are aware of the 50-move rule. 493 moves is very long, but it should still be fairly trivial to get longer games if one just got engines to play and never adjudicate (see example). All one has to do is set some very short time control and play a billion games, and eventually a game will get there.

Games played in tournaments is a different matter, with a necessarily small sample size. In that case I think it's quite likely that 493 moves is the longest on record. It's about 100 moves longer than the next-longest games I'm aware of.

Caveat: the 493-move game wouldn't happen under real tournament rules since the 75-move rule would've been invoked to force a draw.

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