As a Senior Backend Software Engineer, your responsibilities encompass gathering requirements from cross-functional teams and developing fault-tolerant, high-performance distributed systems. You will lead and participate in technical design discussions, gain in-depth domain understanding, and contribute creative ideas. Mentoring other engineers and challenging the status quo while focusing on details and end-user experience will also be key. This role impacts millions of Apple users, requiring a passion for software delivered as a service to maximize reuse, efficiency, and simplicity.