Senior Software Engineer, Backend

Flex is building the AI-native private bank for business owners . We’re re-architecting the entire financial system for entrepreneurs—from the first dollar a business earns to how that value compounds, moves, and is ultimately spent in real life. Banking, credit, payments, personal finance, and financial operations—rebuilt from the ground up as a single, intelligent system. Flex is the full financial home for ambitious owners. Since launching publicly in September 2023 , Flex has scaled from zero to nine-figure annualized revenue , with a clear path to profitability by late 2026 . We move fast, ship relentlessly, and operate with extreme ownership. Our customers are affluent business owners ($3–$200M in revenue) —the backbone of the economy and one of the most underserved segments in finance. They’re stuck with outdated banks and fragmented tools. We’re replacing all of it. The opportunity is massive: a ~$1T+ revenue market hiding in plain sight. Our ambition is to build a $100B+ company by delivering a product that is fundamentally better—not incrementally improved. Flex has raised $100M+ in equity and $300M+ in debt. - Mission-critical problems : We build software that directly controls how money moves at scale. - High bar, low ego : Small teams, exceptional people, real ownership. - Speed over comfort : We prioritize execution, quality, clarity, and results. - Enduring impact : What we’re building will define how a generation of owners runs their businesses. Team & Locations We hire exceptional people who want to build hard things and see their work matter immediately. Roles are available in: San Francisco, Miami, New York, and fully remote. Flex Fuels Ambition. The Role We are looking for engineers who are excited to be part of our early story and help us build a diverse and vibrant company. As a senior software engineer you will have the opportunity to work across the entire stack with a focus on the back-end. You will have the opportunity to learn and drive the creation of financial products and experiences to help our customers reach their full potential. You should have a strong sense of ownership and enjoy taking projects from inception to release. As an early employee, you’ll be working with a nimble team of committed and talented engineers and having a large, long-term impact on technical design and engineering culture. We are open to candidates from Canada, the United States, and Colombia. What You’ll Do Ownership over large domains and features related to card processing/issuing, and core ledgering of financial transactions Play a critical role in the development, design, and maintenance of Flex's platform and services. Architect well thought-out services and data models that ensure Flex's continued growth Own problems end-to-end, thinking through everything from api contracts, data, scalability, security, observability, and metrics. Lead by example and mentor engineers in all aspects of planning, development and testing. Be a catalyst for driving best-in-class technology frameworks and tooling while staying engaged with the latest technology trends. Be on call, with the expectation to ability to solve problems and find solutions for the servicing team What You Need Proficiency in NodeJS+Typescript and server design principles. An understanding and interest in architectural patterns for highly available, scalable, low-latency, asynchronous systems Ability to hold yourself and the team to high standards. Strong communication (written and verbal) and interpersonal skills. Ability to provide in-depth evaluation of multiple technical directions and determine tradeoffs of each. Strong propensity to make data-driven decisions on technical architecture and project prioritization. Exposure to modular monoliths and micro-services along with the benefits and challenges they bring. Experience with any cloud based provider like Google Cloud, AWS, or Azure. Four or more years of relevant industry experience with a track record of shipping high-quality products and features at scale. A strong work ethic and are ready to grind Have built and shipped a working project or product, ideally something complex Compensation Additional Information Interested? We'd love to hear from you At Flex, we value passion, determination, and honesty. Even if you don't fully match the job specifics, we encourage you to apply. Unusual career paths and unique skills can help you stand out. We believe diversity drives our success. Join us at jobs@flex.one Why Join Us Build something generational — Capture the full lifecycle of money for ambitious business owners. Work on real money, real risk — Payments, credit, and banking at serious scale. Solve hard problems — AI, underwriting, compliance, and global finance from first principles. True ownership — Small teams, high trust, real accountability. Founder-level exposure — Direct access to leadership, customers, and investors. High bar, high taste — Move fast without cutting corners. Elite peers — People here are builders, not tourists. Real upside — Meaningful equity if you help build something big.