Karjakin already qualified for 2018 Candidates Tournament as the loser of the World Championship match against Carlsen.
Aronian and Ding Liren already qualified via 2017 World Cup as the top 2 finishers.
Kramnik already qualified as the Wild Card pick from the Russian Organizers.
Caruana and So are virtually in as the top 2 by rating average for the year.
So there are only 2 spots left, which will come from the Grand Prix. Top 2 in total points will qualify.
Mamedyarov and Grischuk are done and in the lead at the moment. However, Radjabov and MVL still have one more GP event coming up in Palma de Mallorca. If they win clear first or even tie for 1st, they will pass the other two.
The winner of the 8-player double-round robin Candidates Tournament will face Magnus Carlsen for a shot at the World Championship!
This is the current Grand Prix Standings after 3 events: