Antifa was never anti-Marxist. They have always been Communists, or Communist supporters:
"The original organization called Antifa was the Antifaschistische Aktion (19321933), set up by the then-Stalinist Communist Party of Germany (KPD) during the late history of the Weimar Republic."
The national socialists version of the antifa was set up against the burgeoning communiust movement in pre war Germany. Then as now the antifa were the Facist anarchists.