It is extremely hard to guess what will Caruana choose against the Najdorf, but this modest-looking move seems to suit his style well.
1. e2e4  1... c7c5  2. g1f3  2... d7d6  3. d2d4  3... c5d4  4. f3d4  4... g8f6  5. b1c3  5... a7a6 