The 50-kilometer Reistad race from Setermoen to Bardufoss in Norway is described as Ski Classics' perhaps toughest course.
Andreas Nygård, who won the Vasaloppet, leads the overall cup on the men's side, followed by Emil Persson and Max Novak from Sweden.
On the women's side, Britta Johansson Norgren is at the top before Ida Dahl.
The competition will also be spiced up with William Poromaa and Ebba Andersson who have both chosen to extend the season with long runs.
Commentators are Jacob Hård and Anders Blomquist.