Senior Software Engineer, Prenatal

Ready to redefine what's possible in molecular diagnostics? Join a team of brilliant, passionate innovators who wake up every day determined to transform healthcare. At BillionToOne, we've built something extraordinary—a culture where transparency fuels trust, collaboration drives breakthroughs, and every voice matters in our mission to make life-changing diagnostics accessible to all. We don't just aim for incremental improvements; we strive to build products that are 10x better than anything that exists today. Our people are our greatest asset: talented scientists, engineers, sales professionals, and visionaries 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—every innovation you contribute helps remove fear of unknown from some of life's most critical medical moments. If you're driven by purpose, energized by innovation, and ready to help build the future of precision medicine, 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.

Projects you may work on include:

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)

Responsibilities:

• 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

Qualifications:

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

Benefits And Perks:

Working alongside brilliant, kind, passionate and dedicated colleagues, in an empowering environment, toward a global vision, striving for a future in which transformative molecular diagnostics can help millions of patients Open, transparent culture that includes weekly Town Hall meetings The ability to indirectly or directly change the lives of hundreds of thousands patients

Multiple medical benefit options; employee premiums paid 100% of select plans, dependents covered up to 80% Extremely generous Family Bonding Leave for new parents (16 weeks, paid at 100%) Supplemental fertility benefits coverage Retirement savings program including a 4% Company match Increase paid time off with increased tenure

Latest and greatest hardware (laptop, lab equipment, facilities) Free daily on-site lunches provided from top eateries A variety of perks on campus (state of the art gym, restaurant) Free on-site EV charging (compatible with all EVs, including Tesla) At BillionToOne, we are proud to offer a combination of a (1) base pay range (actual amount offered is based on experience and salary/equity options split that the candidate chooses), (2) generous equity options offering, (3) corporate bonus program, on top of (4) industry leading company benefits (free healthcare options, 401k match, very generous fully paid parental leave, etc.).

For this position, we offer a total compensation package of $297,321 per year, including a base pay range of $190,081 - $211,201 per year. BillionToOne is an equal opportunity employer. We do not discriminate on the basis of race, religion, color, national origin, gender, sexual orientation, age, marital status, veteran status, or disability status.

For more information about how we protect your information, we encourage you to review our Privacy Policy.

About BillionToOne:

BillionToOne is a next-generation molecular diagnostics company on a mission to make powerful, accurate diagnostic tests accessible to everyone. Our revolutionary QCT molecular counting technology enhances disease detection resolution by over a thousandfold using cell-free DNA—a breakthrough that's already transformed the lives of over half a million patients worldwide.

Our Impact: We've pioneered game-changing diagnostic solutions that are redefining industry standards. Unity Complete™ stands as the only non-invasive prenatal screen capable of assessing fetal risk for both common recessive conditions and aneuploidies from a single maternal blood sample. In oncology, our Northstar® liquid biopsy test uniquely combines treatment selection with real-time monitoring, giving oncologists unprecedented precision in cancer care.

Our Growth: From $0 to $125 million in Annual Recurring Revenue in just four years. We've raised close to $400 million in funding, including a $130 million Series D round in June 2024, achieving a valuation of over $1 billion. This backing comes from world-class investors including Hummingbird, Adams Street Partners, Neuberger Berman, Baillie Gifford, and Premji Invest.

Our Recognition: Forbes recently named us one of America's Best Startup Employers for 2025, and we were awarded Great Place to Work certification in 2024—with an incredible 100% of our people reporting they are willing to give extra to get the job done. These honors recognize not just our innovation but the exceptional culture we've cultivated—one that remains authentically collaborative and transparent even as we've scaled.

Our Future: Headquartered in Menlo Park with facilities in Union City, California, we're continuing to push the boundaries of what's possible in molecular diagnostics. Recent clinical outcomes data for Unity Fetal Risk Screen and new advances in cancer diagnostics prove we're just getting started. At BillionToOne, you'll join a diverse team of passionate innovators who believe that the best science happens when brilliant minds collaborate openly, think boldly, and never lose sight of the patients whose lives depend on our work.

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