Ulhumbrus: Instead of 7 Bb3, 7 Qd2 Be6 8 Bb5 was played in the game Chigorin vs Tarrasch, 19029 h3?! prepares d4 but spends as well a tempo for development upon moving a pawn in the opening. Instead of this 9 Qd2 connects the rooks.
An alternative to 9...Re8 is 9...Ba5 so that on 10 d4 Bxc3 11 bxc3 a further displacement of the d pawn will leave White with a crippled Queen side pawn structure.
11...h6?! spends a tempo for development upon moving a pawn in the opening. An alternative to 11...h6 is 11...Qd7 12 Ng3 Rad8 and Black's rooks are two moves ahead in development of White's rooks.
Instead of 13...b5?! 13...Qd6 14 Re1 Rad8 gains a lead in development.
15...dxc3 is a major concession. It moves the d pawn a third time to exchange it for a c pawn moved once, making a loss of two tempi for development, and it strengthens White's centre into the bargain. It is a sign that things have gone wrong badly for Black.
Two alternatives to 21 d5 are 21 Ne5 with f4 and 21 Nh4 with Nf5 and f4. On 21 Ne5 Carlsen pointed out 21...Qe7 22 f4 Bxb3! 23 Qxb3 Ra3 skewering the white queen to the N on g3. In this sequence an alternative to 22 f4 is 22 Re3! avoiding this combination.
On 21 Nh4 Qe7 22 Nh4-f5 attacks the black queen, giving Black no time to play ...Bxb3.
An alternative to 24 Qd3 is 24 f4 fxe5 25 Rxe5 beginning the plan of Rde1