Senior Full-Stack Software Engineer

Work on a GenAI engineering team building and integrating full-stack software that exercises frontier large language models end to end. You will design, implement, and stress-test applications and tooling that sit on top of pre-release model APIs, collaborate closely with an engineering manager, and deliver production-quality code quickly in a fast-moving research and engineering environment. This is a full-time, 40 hours per week commitment.

• Build and ship full-stack applications, services, and internal tools in one or more of Python, Java, Rust, C#, C++, or TypeScript that exercise frontier model capabilities.
• Integrate pre-release model APIs into working software, including creating tool interfaces, evaluation harnesses, and telemetry systems to observe behavior.
• Diagnose, document, and report model and integration failure modes discovered while building, translating technical observations into clear written feedback for the research team.
• Prototype rapidly against shifting requirements and deliver working increments with limited up-front specification.
• Collaborate with the engineering manager and other engineers to maintain code quality, architecture consistency, 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.
• 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.
• Documented career progression demonstrating increasing responsibility.
• Availability to engage reliably for at least 40 hours per week on weekdays.
• Strong written communication skills and the ability to explain complex technical decisions clearly.

• Location: United States.
• Employment type: hourly, W-2 employment through Cincinnatus LLC as the employer of record, placed as part of an extended workforce on-site or remotely with a leading AI lab.
• Time commitment: full-time, 40 hours per week, weekdays.

Hourly rate range: 90 to 110 per hour.

• This role is offered as W-2 employment through Cincinnatus LLC, which handles payroll, benefits, and employment compliance for placed employees.
• Cincinnatus LLC is an Equal Employment Opportunity employer and does not discriminate on the basis of legally protected characteristics.

The team is intentionally staffed across multiple language ecosystems. Placements and project assignments are organized to ensure coverage across these ecosystems, so candidates should expect to be placed where their language strengths align with cohort needs.

Engineers on this team work directly with the AI lab''s engineering manager on fast-moving projects. Candidates should be prepared to onboard quickly and begin contributing working code early in the engagement. During the early phase you will be expected to implement integrations, prototypes, and diagnostic feedback that inform ongoing research and product development.