Amazon Prime Air designs and operates autonomous delivery drones for fast, environmentally friendly, last-mile package delivery. Ensuring precise localization for autonomous drones within dense urban environments is challenging due to limitations with global navigation satellite system (GNSS)-like multipath interference. The Prime Air Clinic team is trading alternative localization technologies during GNSS-denied phases of flight. Down-selection is supported by data from flight testing with small drones and assessments on accuracy, scalability, cost and weight. Success translates to increasing the robustness of Prime Air drones and supporting Amazon’s commitment to customer obsession.