Bristol Myers Squibb and Johnson & Johnson halted a phase III trial of their factor XIa inhibitor milvexian in acute coronary syndrome after an interim analysis showed the drug was unlikely to meet its primary endpoint. The failure marks another setback for the class of next‑generation anticoagulants seeking safer alternatives to current standards of care. Milvexian remains under evaluation in other phase III indications (e.g., atrial fibrillation, secondary stroke prevention), but the acute coronary syndrome miss will weigh on program economics and investor expectations. The result compounds a challenging year for novel anticoagulants and raises questions about indication selection, trial design, and biomarker strategies for the class. Developers of factor XIa inhibitors may pivot to smaller, better‑stratified populations or revisit dosing and combination approaches. The outcome will influence investment appetite and partnership decisions across anticoagulant R&D.