I’m not sure. I’ve read a few north of 1,000 pages. 1Q84 by Haruki Murakami and Atlas Shrugged by Ayn Rand leap to mind. I don’t read too many very long books as I generally find they are badly in need of editing. [That is certainly the case for Atlas Shrugged.] And, you know, they take a long time to read.
The fattest book on my physical bookshelf at the moment is Stephen Wolfram’s A New Kind of Science, but I’m pretty sure I never got through that one.
Tiger Riding for Beginners 