Senior Software Engineer Infrastructure / Platform

KTS is hiring on behalf of a fast-growing YC-backed AI startup building core infrastructure used by frontier AI labs. We are looking for a Senior Software Engineer Infrastructure / PlatformThis is a high-ownership engineering role for someone who wants to build the platform layer behind large-scale data generation, evaluation systems, human-in-the-loop workflows and agentic AI experimentation. You will work directly with the founding team to design and build the shared infrastructure that enables engineers and researchers to run high-throughput workflows reliably at scale.This is not a standard backend role. The ideal candidate has strong production infrastructure experience, deep systems judgement, and the ability to build reliable platforms in a fast-moving, early-stage environment.What you’ll work onYou will help architect and build the infrastructure powering data generation platforms, evaluation pipelines and human-in-the-loop systems used in frontier AI development. You’ll create reusable APIs and internal platforms, improve reliability and observability, design high-throughput async processing systems, and help define engineering standards across deployment, infrastructure, system design and operations.What we’re looking forStrong candidates will bring:5+ years building production distributed systems, backend platforms or core infrastructureStrong Python and/or JavaScript/Node.js/Next.js experience, or similar backend technologiesExperience designing and operating cloud systems on AWS or GCPHands-on experience with message queues and event-driven systems such as Kafka, RabbitMQ, Pub/Sub or similarStrong understanding of scalability, reliability, performance, observability and fault toleranceExperience owning production systems used at scaleBackground from a high-growth startup, top-tier engineering company or FAANG-equivalent environmentComfort working closely with founders, engineers and researchers in a high-velocity environmentBonus points for experience with AI infrastructure, LLM evaluation systems, ML pipelines, human-in-the-loop workflows, workflow orchestration, large-scale data processing or internal developer platforms and top-tier university.Why this role is excitingYou’ll be joining an early, high-calibre team building infrastructure that directly supports the next generation of AI development. This is a chance to own major technical decisions, shape platform architecture from an early stage, and work with world-class engineers and researchers on systems that need to be fast, scalable and reliable from day one.Location: San Francisco, in-personEmployment: Full-timeHiring process: Recruiter screen, technical conversations, system design rounds, work trial, references and offer