Three-year follow-up of the phase 3 KEYNOTE-966 trial confirms that adding pembrolizumab to gemcitabine and cisplatin maintains a durable overall survival benefit in advanced biliary tract cancer, with no new safety signals reported. The long-term readout is designed to address durability and tolerability questions that can emerge after earlier interim analyses. For oncology decision-makers, the persistence of benefit beyond the initial trial window strengthens the case for pembrolizumab-based combination strategies as a treatment standard in a disease area where survival improvements have historically been incremental. The update also reinforces trial design relevance for subsequent studies layering checkpoint blockade with other modalities in biliary cancers, where biomarker strategy and patient selection will likely remain central.