[aoanla]

This seems to be a thing that Stephenson likes: The Diamond Age has apparently deliberate significant changes in style and genre across it, Cryptonomicon is part very-near-future tech thriller and part-1940s spy thriller, Seveneves (as noted elsewhere here) has a big genre change some way through, and arguably The Rise and Fall of D.O.D.O also blends a few different genres together, some of them historical. He's certainly more egregious about it in Fall, but it's something he obviously likes doing...