Biliary tract cancer continues to show durable benefit with pembrolizumab plus chemotherapy. Three-year follow-up of the phase 3 KEYNOTE-966 trial confirmed an ongoing overall survival advantage from adding pembrolizumab to gemcitabine and cisplatin in advanced disease, with no new safety signals reported. The long follow-up strengthens the case for sustained checkpoint inhibitor exposure in a tumor type where post-progression options can be limited. It also provides additional evidence for clinicians weighing time-on-therapy tradeoffs. For development planners, the result may raise confidence for further combinations in biliary tract malignancies, including in earlier lines or biomarker-selected populations, given the persistence of benefit beyond initial response windows.