This is a phase 3 randomized, multicenter, non-inferiority open-label RCT. 190 eligible APS patients with arterial or venous thrombotic history receiving acenocumarol will be stratified according the presence of SLE and venous/arterial thrombotic history and randomized (1:1) either to continue vitamin K antagonists (standard of care, normalized ratio (INR) 2-3 or 2.5 to 3.5 in those with recurrent thrombotic episodes) or to switch to rivaroxaban (20 mg/day). The primary efficacy outcome is the development of any thrombotic event during the study period. Secondary efficacy outcomes include time to thrombosis, type of thrombosis (arterial or venous), overall causes of death, evaluation of a prognostic biomarker panel of recurrent thrombosis. The primary safety outcome will be major bleeding. Secondary safety outcomes include any adverse event and minor bleeding.