Staff / Principal / Lead Backend Software Engineer

Backend / Python Software Engineer — Staff / Principal / Lead San Francisco, CA — Onsite Full-Time Relocation Assistance Available | H-1B Transfer Supported About the Role We are hiring a Staff / Principal / Lead Backend Engineer for a well-funded San Francisco fintech startup building next-generation infrastructure across banking, payments, digital wallets, and cryptocurrency. The platform handles real money at international scale, integrating with banking providers, cryptocurrency wallets, payment rails, authentication systems, ledgers, and other financial services. You will work directly with the technical founders and take significant ownership of the backend architecture, engineering standards, scalability, reliability, and security of the platform. The current backend is a Python / FastAPI monolith running on AWS with PostgreSQL and Redis, with the flexibility to introduce Go or Rust services where performance or scale requires it. What You'll Do • Design, build, and scale mission-critical backend systems and APIs • Own architecture across payments, wallets, ledgers, and financial integrations • Build highly reliable systems where transaction accuracy and data integrity are critical • Improve performance, scalability, fault tolerance, and observability • Design APIs, database models, and distributed system components • Integrate with banking, payment, crypto, authentication, and compliance providers • Make key technical decisions alongside the founders • Mentor engineers and help establish backend engineering standards as the team grows What We're Looking For ✓ 5+ years of backend software engineering experience ✓ Strong production experience with Python ✓ Experience building and operating high-scale backend applications ✓ Strong knowledge of FastAPI or similar Python web frameworks ✓ Experience with PostgreSQL, Redis, and AWS ✓ Strong understanding of system design, APIs, databases, scalability, and reliability ✓ Proven ownership of production systems from design through deployment and operation Highly Preferred Experience building financial technology involving one or more of: • Payments / Payment Processing • Transaction Ledgers / Double-Entry Accounting • Digital Wallets • Banking Infrastructure • Settlement & Reconciliation • Fraud / Risk Systems • AML / KYC • Crypto / Blockchain / Stablecoins Experience with Go, Rust, Kafka, Docker, Kubernetes, Terraform, CI/CD, or event-driven architectures is a plus. We particularly value engineers who have architected systems, built products from scratch, scaled high-volume platforms, reduced latency, improved reliability, or owned critical production infrastructure.