We are looking for a founding backend engineer with unusually strong engineering and design taste. The world’s most critical infrastructure—banking, airlines, utilities—is held together by millions of lines of COBOL and mainframe logic written decades ago. The engineers who built it are retiring and the documentation is fading. These systems are "too big to fail" and "too complex to change," leaving global infrastructure frozen in the 1970s. At Hypercubic, we’re building AI systems that can understand, reason about, and rearchitect large-scale legacy applications. We work at the intersection of program analysis, knowledge extraction, and agentic systems, applied to some of the most critical enterprise software in the world. Learn https://www.hypercubic.ai/insights/mainframe-modernization-is-a-hard-and-fun-problem-to-solve why we're excited about mainframe modernization. ABOUT THE ROLE We’re looking for a backend engineer with unusually strong engineering and design taste. You will work directly with the CTO to design, prototype, and productionize AI-powered systems from first principles. This is a founding role with meaningful ownership over architecture, product direction, and engineering culture. It is suited for someone with strong fundamentals and comfortable operating across abstraction layers, from low-level system reasoning to high-level interactions. WHAT YOU’LL DO - Rapidly prototype new concepts and features to validate ideas before full implementation. - Ship AI-driven features end to end, from model interaction to user-facing workflows. - Set early engineering standards around testing, reliability, and code quality. - Translate ambiguous problem statements into concrete experiments, constraints, and working systems. - Lead architecture decisions and long-term technical direction with the CTO. - Collaborate with a highly diverse group of subject matter experts and customers from various industries (banks, insurance, airlines, and more). YOU ARE A FIT IF… - You care deeply about your work and the product. - You are comfortable with uncertainty and enjoy figuring out what to build before how to build it. - You have built complex agentic products or infrastructure. - You think in systems and feedback loops, not just features. - You can move fast and slow. Prototyping ideas in hours, then building enterprise-grade features to a high-quality bar. - You want to become world-class at AI engineering. - You have a bias for action and a track record of working in fast-paced environments with urgency. NICE TO HAVE - Strong testing intuition, including TDD and property-based testing. - Experience building and maintaining production-grade agentic or autonomous systems. - Exposure to legacy systems (especially mainframes or COBOL), compilers, program analysis techniques, or high-performance computing (HPC). - Familiarity with enterprise software constraints. LOGISTICS - Location: This role is in-person based in San Francisco, California. - Benefits: Hypercubic offers generous health, dental, and vision benefits, PTO, and relocation support as needed. - Sponsorship: Unfortunately, we are unable to sponsor new H1B employment visas at this time. However, we can support H1B transfers and OPT.