What is the opening with the most book moves in chess?

I recently played the King's Indian Defense: Normal Variation, 4.e4 d6 5.Nf3 c5 6.dk O-O with 6 book moves in it, so I got curious as to what is the opening with the most book moves.

I just found that The Sicilian defense: Open, Najdorf, Poisoned pawn variation accepted has 9 book moves:

https://www.chess.com/openings/Sicilian-Defense-Open-Najdorf-Poisoned-Pawn-Variation-Accepted

Do you just mean, in chess.com's book?

Or modern book theory?

That Najdorf game that I keep showing around followed book until my novelty on move 28.

I mean in chess.com's book moves.

I think Berlin Defense could go up to 40 moves force draws.. I've heard it somewhere. Kindly check it out 😅

All I could find was this three- move opening: https://www.chess.com/openings/Ruy-Lopez-Opening-Berlin-Defense

There is so much more than that brother. 😅 

Fried Liver Attack has 12 book moves 

Sorry for replying this late, but the Ruy López Opening: Marshall Attack, Modern, Main Line, Spassky Variation has 18 book moves.

Najdorf has a ton

my candidates are sicilian najdorf and ruy-lopez marshall / spassky

Sometime i just want to say i don't give shit with all this so called either opening theory or opening book

Thanks for the information.

A99 Dutch 16 book moves
B99 Najdorf 21 book moves
C99 Ruy Lopez 21 book moves
D99 Grünfeld 22 book moves
E99 King's Indian Defence 23 book moves

Nice.

     Probably the Queen's Gambit if you count all the QGA, QGD, Slav (just another way of declining), Tarrasch, Albin and on and on and on.