As far as I remember, Anand was(is) primarily an 1.e4 player throughout his career. Yet in the first game of the Carlsen-Anand match he opted to open with 1.d4. What are the potential benefits of such an opening choice in a situation like this? Is Anand simply wary of having to face the Berlin Defense, or is there another benefit to choosing 1.d4?
Anand primarily played 1. d4 in each of his 3 successful world championship matches between 2008 and 2012. In his 2013 match vs. Carlsen he favored 1. e4 before switching to 1. d4 for his last white of the match (game 9). Given the disastrous result of the 2013 match for him, I don't think it's surprising that he is apparently relying on 1. d4 this time.