Chess.com does not publish a single absolute world‑record number (because the opening library updates over time, and ultra‑long forced lines are rare). However, from public data and forum discussions:
This line is frequently cited as one of the longest, with some sequences reaching up to 36 total plies (18 moves for each side). longest book move sequence chess.com
The Poisoned Pawn Variation and other main lines in the Najdorf are heavily analyzed, with theory often lasting 25 to 30 moves . longest book move sequence chess.com