1. c2c4  1... g8f6  2. b1c3  2... e7e5  3. g1f3  3... b8c6  4. g2g3  4... d7d5  5. c4d5  5... f6d5  6. f1g2  6... f8c5 This variation has become popular since Caruana used it in his 2018 match against Carlsen. Of course there is nothing wrong with the main line, 6...Nb6. 7. e1g1  7... e8g8  8. d1c2 A new try. This move was played by Carlsen in a rapid game this year. 8... c6d4 The game quickly goes down little-trodden paths. 9. c2e4 The first new move. 9... d5c3  10. d2c3  10... d4f3  11. e2f3 The precise way to capture. Otherwise Black can try a plan with f5-e4, gaining space. Now White can press on the e-file and play f3-f4 at some point. 11... f8e8  12. f1e1  12... c7c6  13. f3f4  13... d8b6 Now it's not so easy to protect the f2-pawn. 14. c1e3 The exchange of the b2-pawn for the e5-pawn leaves the position unbalanced and sharp. 14... c5e3  15. e4e3  15... b6b2  16. f4e5  16... c8f5 An important move, developing the bishop and controlling the b1-square, preventing one of the rooks from threatening the black queen. 17. a2a4 Gaining space on the queenside and removing the pawn from a potential capture by the opponent's queen. 17... f7f6  18. f2f4  18... a8d8  19. g2f1  19... f6e5  20. f1c4  20... f5e6 This is not the best. The game finishes in perpetual check after the correct 21. a1b1 Now the position is dangerous for Black. 21... b2c2  22. c4e6  22... e8e6  23. b1b7  23... e6h6 The most natural move, especially in a rapid game. Computer analysis shows many subtleties in this position and it would be impossible to calculate everything in such a short time. To begin with, the best moves according to the machine, 23...a5 or 23...h6, are very difficult to play. 24. b7g7 This looks like a winning tactical shot, but actually it's not the best move. To prove this, however, requires machine-like precision. 24... g8h8  25. h2h4 Now it's all over. 25... h6e6  26. g7g5  26... e5e4  27. f4f5  27... e6e7  28. f5f6  28... e7f7  29. e3e4  29... c2c3  30. e4e8  30... f7f8  31. f6f7 A nice final tactical move.There is no defense to the threat of 32.Rg8+.