Principal Software Engineer - M365 Core

You'll join the Experimentation and Configuration Service (ECS) team, where you'll build infrastructure that operates at massive scale with billions of requests per day. We're the team that customers trust to deliver configuration changes safely, quickly, and reliably. Our client SDKs are the critical interface between services and the ECS platform, and we're looking for engineers who want to solve hard problems in security, resilience, and distributed systems. As a Principal Software Engineer working on the ECS Client SDK, you'll own the development of client libraries that provide security, resilience, and observability for mission-critical services. You'll design and implement features like authentication, caching with multi-layer fallbacks, telemetry, and failure recovery mechanisms. You'll collaborate with service teams across Microsoft to understand their operational challenges and translate them into reusable SDK capabilities that benefit the entire ecosystem.