Senior Software Engineer, Prenatal

Join a team of brilliant, passionate innovators determined to transform healthcare. At BillionToOne, we've built a category-defining, publicly traded company on Nasdaq where transparency fuels trust, collaboration drives breakthroughs, and every contribution moves the needle on our mission to make life-changing diagnostics accessible to all. We don't just aim for incremental improvements; we build products that are 10x better than anything that exists today.

Our scientists, engineers, sales executives, and visionaries are united by an unwavering commitment to changing the standard of care in prenatal and cancer diagnostics. This is where cutting-edge science meets human compassion, and every innovation you contribute helps remove the fear of the unknown from some of life's most critical medical moments.

If you're driven by purpose, energized by innovation, and ready to help shape the future of precision medicine at scale, this is where you belong.

We are currently looking for a high-performing Senior Software Engineer, Prenatal to join our dynamic software engineering team. Software engineers at BillionToOne work in highly collaborative and interdisciplinary teams of clinicians, computational biologists, and other engineers to robustly scale personalized genomic medicine to millions of patients. If you have experience performing in a full life-cycle development, love seeing your work positively affect your colleagues and patients, and thrive in a fast-paced entrepreneurial environment, this could be a great opportunity for you. In this role, you can have an impact both through many small tools and large product development. This role is a hybrid (onsite 2-3 days/week) position.

• Scaling and future-proofing core systems to support rapid volume growth, enterprise workloads, and long-term platform expansion.
• Building shared platform libraries and modular, domain-aligned services that reduce coupling, improve maintainability, and enable teams to integrate and deliver independently.
• Driving core architectural initiatives including service boundaries, data flows, observability patterns, and modernization of legacy components to enhance reliability and developer velocity.
• Establishing foundational infrastructure and automation that strengthens deployment workflows, improves system health visibility, and enables consistent, high-quality engineering execution.

Technologies we use include: Python, Django, Postgres, React, Typescript, AWS, Heroku, Salesforce, and emerging AI-assisted coding environments (e.g., Cursor, GitHub Copilot, Claude Code)

• →Design, build, and operate scalable, high availability backend services, APIs, and data integrations that power customer facing product experiences
• →Lead technical delivery across the full lifecycle: architecture, design, implementation, testing, deployment, and ongoing operations
• →Collaborate closely with product, design, and cross functional engineering teams to deliver performant, reliable, and intuitive platform capabilities
• →Develop clean abstractions and platform APIs that simplify complex LIS workflows while balancing developer velocity with long term system stability
• →Build and maintain secure, reliable cloud infrastructure on AWS, including compute environments, networking, container orchestration, storage, and environment automation
• →Implement CI/CD pipelines, Infrastructure as Code, configuration management, and automated environment provisioning to standardize and accelerate delivery
• →Embed observability and operational excellence into the platform by default through robust monitoring, logging, alerting, and reliability patterns
• →Ensure the scalability, maintainability, and overall health of backend and cloud systems as the platform grows to support large enterprise workloads and future global expansion
• →Foster a culture of ownership, technical excellence, learning, and continuous improvement within the engineering team
• →Apply AI-assisted tooling and workflows to improve developer productivity, automate routine engineering tasks, enhance code quality, and accelerate troubleshooting

• 5 - 7 years of professional software development experience with a proven track record of delivering complex projects adhering to best practices
• Deep understanding and experience using web frameworks like Django and FastAPI
• Strong system design and architecture capabilities, applying domain-driven design to translate complex business domains into clear, scalable service and data boundaries.
• Familiarity with modern AI-driven development practices and tools.
• Strong foundation in cloud services, preferably AWS, including ECS, S3, AWS Batch, EC2, and AWS Lambda, enabling effective architecture and management of complex systems
• Excellent communication and collaboration skills, with the ability to work effectively in a team-oriented environment
• Excited about working in-person with our team in Menlo Park

Unity Complete™ is the only non-invasive prenatal screen capable of assessing fetal risk for both common recessive conditions and aneuploidies from a single maternal blood sample. Our Northstar® liquid biopsy test uniquely combines treatment selection with real-time monitoring, giving oncologists unprecedented precision in cancer care.

From $0 to $150M+ in Annual Recurring Revenue in just five years. In 2025, we completed one of the most successful IPOs for a medical diagnostics company, building on nearly $400M in private funding,including our $130M Series D in 2024 and backed by world-class investors including Hummingbird, Adams Street Partners, Neuberger Berman, Baillie Gifford, and Premji Invest.

Forbes named us one of America's Best Startup Employers for 2025 and we're Great Place to Work certified, with 100% of our people willing to go the extra mile, even as we've scaled to over 700 employees.

Headquartered in Menlo Park with facilities in Union City, CA, and a new lab opening in Austin, TX in 2027, we're continuing to push the boundaries of what's possible in molecular diagnostics. We're just getting started.

Ready to help us change the world, one molecule at a time? Learn more at billiontoone.com