Senior Full-Stack Software Engineer

Build and ship full-stack systems that exercise cutting-edge large language models before they are released, integrating pre-release model APIs into real software and delivering production-quality code quickly. You will be placed on a GenAI engineering team at a leading AI lab, working directly with the engineering manager on fast-moving projects and contributing functioning code early in each engagement.

• Develop full-stack applications, internal tools, and services in Python, Java, Rust, C#, C++, or TypeScript that exercise frontier model capabilities end to end.
• Integrate pre-release model APIs into working software, including building tool interfaces, evaluation harnesses, and telemetry around model behavior.
• Diagnose, document, and communicate model and integration failure modes discovered while building, converting engineering observations into clear feedback for research teams.
• Prototype and iterate rapidly against shifting requirements, delivering working increments with limited up-front specification.
• Collaborate with the engineering manager and other engineers to maintain code quality, consistent architecture, and up-to-date technical documentation.

• 6+ years of professional experience building and shipping production software at a recognized, top-tier organization, with end-to-end ownership of systems.
• Deep production experience in at least one of Python, Java, Rust, C#, or C++, plus demonstrated delivery in a second language from a different ecosystem. This cohort is intentionally staffed across multiple language ecosystems.
• Hands-on ownership across the stack, including backend service and API design, a modern front-end framework such as React or equivalent, data modeling, and cloud deployment and operations.
• Proven ability to onboard into unfamiliar codebases and deliver working code quickly with minimal ramp-up.
• Clear career progression and strong written communication skills, able to explain complex technical decisions.
• Ability to engage reliably for at least 40 hours per week during weekdays.

• Employment type: hourly, W-2 position employed by Cincinnatus LLC.
• Placement: you will be placed as part of the AI lab''s extended workforce to work directly within the client team.
• Time commitment: full-time, 40 hours per week, weekday availability required.
• Location: United States based placement.

Hourly pay range: 90 - 110 hourly.

• This is a W-2 employment position with Cincinnatus LLC, which serves as the employer of record and places employees with client engineering teams.
• Cincinnatus is an Equal Employment Opportunity employer. Decisions are made without regard to race, religion, color, national origin, sex, sexual orientation, gender identity, gender expression, age, protected veteran status, disability, genetic information, political views, or any other legally protected characteristic.

Selected candidates will be employed by Cincinnatus LLC and placed at the client AI lab. In that placement you will work directly with the engineering manager on fast-paced projects, onboard quickly, and are expected to deliver working code early in the engagement.