It's Magnus's Birthday. The Champion is 31 today, and most people are expecting (who knows why) him to push hard and get the first win in the match. Sunday, during her live commentary, Judit Polgar said that she happened to play important games on her birthday, and that's not always been easy.
Game 4 started with a Petrov's defense, the very mainline.
At move 9, Magnus played Re1, which is not a novelty, but neither a super-common move in the opening.
Ian thought a bit too much on move 9 and then went for Bf5.
By move 14, the game was still in theory.Looking at Ian and Magnus's moves in the first part of the game, one feels that both players wanted an easy day at the office. By move 17, they were playing an endgame already. But it was not the case. At move 18, Magnus played Nh4. A move that engines don't like particularly, but which had Ian think a bit. Probably the Russian didn't expect such a move.
The plan was to bring the Knight to g2.At move 21, Magnus played Bf4, the move engines wanted, showing his flawless preparation. Ian fell into a long deep thinking phase.
Ian took the bishop after a relatively long time, and Magnus replied immediately, coming out of the exchange with a dominating Knight in d5. At move 27, Magnus avoided a repetition that would have led to a draw and played the natural d5. The Champ was trying to win, or at least to make it hard for his opponent.
After Ian's 27…a4, all of a sudden, the game got sharp. A slight mistake now would have meant defeat. After move 29, Magnus thought for a long time, evaluating the tricky position. The commentators were going through tons of variations without finding anything decisive. It looked like the topic moment of the game. After 35 minutes(!) Magnus went for Nf8+. Carlsen sat still, blinking his eyes at a rapid pace, without changing his facial expression. Not a usual thing to see.
Magnus, in his amazingly long thinking moment, didn't find anything decisive for white. The players repeated the moves once again. Now Carlsen had the chance to claim a draw with the third repetition, and he spent more time trying to devise an effective plan. There was no way for the Norwegian Champ to find something practical for white, and after another repetition, they agreed to a draw.
In the short interview right after the game, Carlsen said he tried, but he just didn't find it. And that he is not frustrated at all, as it's normal to try and OK not to find a win over the board.