Principal / Senior Software Engineer

The Company FL105 is a privately held, early-stage company pioneering the use of artificial intelligence to transform human psychological fitness and wellbeing. We are creating a platform that empowers people to build a life they are proud of and fulfilled by. FL105 is backed by Flagship Pioneering, an innovation enterprise that conceives, creates, resources, and builds companies that invent breakthrough technologies that transform the world. Flagship has created over 100 groundbreaking companies since 2000, including Moderna. The Role We are seeking an experienced, creative, and talented Principal / Senior Software Engineer. The ideal candidate will have a strong background in software and product development, with the ability to lead projects and communicate effectively across teams and with ML researchers. Key Responsibilities In this role, you will: Lead the design and development of customer-facing features across the front-end and back-end application stack. Partner closely with product managers, designers, and researchers to translate customer needs and product strategy into well-designed, high-impact features. Own features throughout the full product development lifecycle, from discovery and technical design through implementation, release, measurement, and iteration. Manage the release process for new features, including rollout planning, feature flagging, monitoring, and coordination across engineering and product teams. Use product analytics, feature experiments, and customer feedback to evaluate feature performance and guide continued development. Design scalable system architecture for rapidly evolving, AI-enabled back-end components. Contribute to user interface and interaction design, bringing technical insight into product and design decisions. Improve application delivery practices by implementing continuous integration, continuous delivery, automated testing, and operational best practices. Leverage AWS cloud infrastructure to build scalable, reliable, and efficient applications and AI-powered services. Uphold high standards of data security, privacy, and compliance across all applications. Successful candidates will be able to thrive in a fast-paced, action-oriented, team environment and display a clear passion for AI innovation and impact. The role offers a unique opportunity to help drive the strategy of an early stage AI-focused company. The candidate must be an entrepreneurial, highly motivated, and purpose-driven individual. The successful candidate will have a track record of building consumer applications or large internal applications. They must exhibit strong collaboration and communication skills. They should be ready to lead application development in a very dynamic and innovative environment. Qualifications: 5+ years of experience in software development, with a strong focus on building applications. Extensive experience with AWS services (including ECS, S3, Lambda, etc) or a similar cloud services provider. Proficient in Python. Demonstrated ability to build scalable, efficient, and secure software applications. Motivated and team oriented, with an ability to thrive in a multidisciplinary environment. Excellent communication and collaboration abilities. Preferred Qualifications: Experience with LLM development. AWS Certifications, such as Solutions Architect Associate or Professional. Able to build applications using the AWS CDK and Typescript. Knowledge of security best practices for SaaS solutions. About Flagship Flagship Pioneering is a bioplatform innovation company that invents and builds platform companies, each with the potential for multiple products that transform human health or sustainability. Since its launch in 2000, Flagship has originated and fostered more than 100 scientific ventures, resulting in more than $90 billion in aggregate value. Many of the companies Flagship has founded have addressed humanity’s most urgent challenges: vaccinating billions of people against COVID-19, c