Three-year follow-up from the Phase 3 KEYNOTE-966 trial confirms that adding pembrolizumab to gemcitabine plus cisplatin maintains a durable overall survival benefit in advanced biliary tract cancer, with no new safety signals reported. The update strengthens the evidence base for continued first-line checkpoint inhibitor use alongside chemotherapy. For oncology teams, the longer-duration dataset narrows the gap between earlier readouts and durability questions that often shape uptake decisions and guideline positioning.