Senior Software Engineer, Oncology at Billiontoone

Ready to redefine what's possible in molecular diagnostics? 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. With over 700 employees, half a million patients helped, and one of the most successful IPOs in medical diagnostics history behind us, we're just getting started. 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 to join our dynamic software engineering Oncology 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: • Build a seamless digital experience so clinicians and patients across a diversity of care centers and socioeconomic status can have access to BillionToOne’s highly complex genetic testing • Help digitize laborious and error-prone paper-based workflows at busy Oncology clinics • Enable better transfer of care through portable electronic medical records Technologies We Use: Python, Django, Flask, Postgres, AWS, Alpine.js, HTMX, Salesforce, and emerging AI-assisted coding environments (e.g., Cursor, GitHub Copilot, OpenAI). Responsibilities: • Collaborate with talented engineers to design and develop our backend services, data processing pipelines, and interfaces, driving innovation and efficiency • Build user-facing features to optimize performance and reliability, enhancing overall user experience • Elevate BTO Oncology’s backend systems, including the test order record database, third-party integrations, test scheduling and reports management software, and distributed systems architecture, to ensure they meet the highest standards • Demonstrate a creative and out-of-the-box mindset, offering innovative solutions and approaches to complex technical challenges • Prioritize quality by writing comprehensive unit / integration / end-to-end tests and ensuring superior test coverage across all components and modules. Highly skilled in writing technical documentation and validation reports that assure correct functionality of medical informatics systems • Demonstrate a strong sense of ownership and take responsibility for end-to-end project delivery. The ideal candidate will thrive in an environment where they have the autonomy to make informed decisions and take the initiative to drive projects forward • Collaborate cross-functionally, actively seeking input from team members and fostering a positive and inclusive work environment Qualifications: • 5+ years of professional software development experience with a proven track record of delivering complex projects and adhering to best practices • Expertise in Python backend frameworks (e.g., Django or Flask), delivering high-quality, scalable code • Strong foundation in cloud services, preferably AWS, including ECS, S3, AWS Batch, EC2, and AWS Lambda, enabling effective architecture and management of complex systems • Familiarity with modern AI-driven development practices and tools • Excellent communication and collaboration skills, with the ability to work effectively in a team-oriented environment • Proven track record of building products and features from conception to deployment, showcasing your ability to innovate and deliver results Nice-to-haves: • Experience in healthcare-related software or a passion for improving healthcare systems • Experience working at a fast-paced startup or high-growth company • Familiarity with healthcare data standards, such as FHIR and HL7 • Experience with medical software and authoring technical verification / validation reports • Experience leveraging AI-assisted coding and debugging tools • Experience building AI agents, fine-tuning machine learning models, or deploying LLM-based applications If you’re passionate about creating technology that transforms healthcare and thrive in a collaborative, fast-paced environment, we’d love to hear from you. 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) • 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 $307,321 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. 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 has already transformed the lives of over half a million patients worldwide. Our Impact 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. Our Growth 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. Our Recognition 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. Our Future 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