Principal Backend Engineer

Flagship Pioneering, Inc.•Cambridge, MA

5d•$188,000 - $258,500•Onsite

About The Position

As a Principal Backend Engineer, you’ll be a technical leader responsible for architecting, building, and scaling the core backend systems that power our agentic platform. You’ll drive the design of high-throughput services, resilient data pipelines, real time agent clouds, and integrations with mission-critical third-party providers. You’ll translate complex requirements into robust, elegant systems that support rapid growth. You’ll be a key contributor to our technical strategy, helping evolve our platform architecture to maintain security and reliability as we scale.

Requirements

8+ years of backend engineering experience.
Experience with high velocity agentic coding under strict security requirements.
Bachelor’s degree in Computer Science, Software Engineering, or equivalent practical experience.
Strong expertise in backend languages and frameworks (Node.js/TypeScript, Go, Python, or similar).
Experience designing scalable distributed systems, microservices, and event-driven architectures.
Deep experience with third-party integrations, REST/GraphQL APIs, webhooks, and rate-limited services.
Proficiency with SQL/NoSQL databases, data pipelines, and performance optimization.
Familiarity with cloud platforms (AWS, GCP) and containerized/deployed systems (Docker, Kubernetes).
Strong testing, CI/CD, and observability practices.
Comfortable working in a fast-paced, evolving environment with minimal oversight.

Nice To Haves

Experience building and shipping features quickly in early-stage startups.
Exposure to multiple backend domains (analytics, payments, notifications, workflow orchestration).
Hands-on experience with serverless or edge architectures for rapid iteration.
Familiarity with low-friction integrations with third-party tools and SaaS platforms.
Track record of scaling systems from small MVPs to production-ready services.
Comfort with ambiguity and making trade-offs between speed, quality, and maintainability.

Responsibilities

All things AI agents – from harness selection to prompt optimization and eval system, you’ll work side by side with your teammates to deliver best in class agent experiences.
Own Core Backend Systems – Design, build, and maintain scalable services, APIs, and platform infrastructure. Ensure reliability, observability, and maintainability.
Build and Maintain Large-Scale Data Pipelines – Architect and operate high-volume, resilient data pipelines for ingestion, transformation, and analytics.
Lead Third-Party Integrations – Build and maintain integrations with external vendors, ensuring reliability, observability, and long-term maintainability.
Influence Architecture & Best Practices – Shape backend architecture, coding standards, testing frameworks, CI/CD pipelines, and operational excellence.
Wear Multiple Hats – Support DevOps, troubleshooting, or other platform needs when necessary.