Frontend-Focused Full Stack Engineer

$50-$65/hour | Full-time, 40 hours/week | United States | W-2 This is a frontend-focused full-stack engineering opportunity supporting a leading AI lab. Engineers build, integrate, and stress-test production software around frontier models, with hands-on work across React or an equivalent frontend framework, TypeScript, backend services, APIs, databases, and cloud deployment. What you'll do • Build and ship full-stack applications, internal tools, and services that exercise frontier model capabilities end to end. • Develop responsive frontend interfaces and integrate pre-release model APIs. • Build evaluation harnesses, tool interfaces, telemetry, and supporting application infrastructure. • Diagnose model and integration failures and translate findings into clear technical feedback. • Prototype quickly against changing requirements while maintaining strong code quality and documentation. What we're looking for • 3+ years of professional experience building and shipping production software at a recognized organization. • Production experience in Python, Java, Rust, C#, or C++, plus working proficiency in a second language. • Hands-on experience across the stack, including React or an equivalent frontend framework, APIs, databases, and cloud deployment. • Strong TypeScript and modern web-development judgment. • Ability to work reliably for 40 hours per week on weekdays. • Clear written communication and the ability to explain technical decisions. Employment This is a full-time W-2 position with Cincinnatus LLC, with the opportunity to join a leading AI lab as part of its extended workforce. Apply directly through Mercor: https://work.mercor.com/jobs/list_AAABn8oCPAhaAFmwEEhPDYO5/software-engineer-full-stack-python-java-rust-c-c?referralCode=e9602361-4eb5-474f-9c0c-5d1fe341d07b&utm_campaign=job&utm_content=list_AAABn8oCPAhaAFmwEEhPDYO5&utm_medium=direct&utm_source=referral Applications, assessments, selection, employment terms, and role availability are managed by Mercor. HumanitApp is independent and may receive referral credit. We consider all qualified applicants without regard to legally protected characteristics and provide reasonable accommodations upon request.