Senior Software Engineer, Full Stack (Python, Java, Rust, C#, C++)

HumanitApp; Northern (KY); Hybrid; USD 124,000 - 152,000; Full time

Job summary

HumanitApp is seeking Senior Full-Stack Software Engineers to join a leading GenAI team building foundational AI models and integrating frontier model APIs. You will work across Python, Java, Rust, C#, C++, and TypeScript to deliver production-ready software and tools that enable AI research.

This full-time W-2 position with Cincinnatus LLC places you at a top AI lab, offering hands-on ownership, fast ramp-up, and collaboration with a talented engineering manager to ship end-to-end solutions.

Qualifications

• 6+ years building and shipping production software at a top-tier organization.
• Proven delivery in at least two languages across different ecosystems.
• Hands-on ownership across backend, frontend, data modeling, and cloud deployment.
• Ability to onboard quickly to an unfamiliar codebase and deliver working code with minimal ramp-up.

Responsibilities

• Build and ship full-stack applications, services, and internal tools in Python, Java, Rust, C#, C++, or TypeScript.
• Integrate pre-release model APIs into working software and tooling.
• Diagnose and document model and integration failures for the research team.
• Prototype quickly against shifting requirements and deliver increments.
• Collaborate with the engineering manager and others to maintain code quality and architecture.

Skills

6+ years exp

Python/Java/Rust/C#/C++

Frontend: React

API design & cloud

Strong communication

Tools

React or equivalent

API design

Job description

Join a leading AI lab's cutting-edge GenAI team to be at the core of the AI revolution, where your expertise fuels the development of the most advanced Large Language Models.

1. Overview

Join a leading AI lab's cutting-edge GenAI team and help build foundational AI models from the ground up. We're seeking talented Senior Full-Stack Software Engineers with deep, hands-on production expertise across modern application stacks

Python, Java, Rust, C#, C++, and TypeScript

to build, integrate, and stress-test real software on top of frontier models before they ship. Engineers work directly with the AI lab's engineering manager on fast-moving projects and are expected to onboard quickly and contribute working code early. This is a full-time commitment of 40 hours per week.

This is a W-2 employment position with Cincinnatus LLC, with the opportunity to be placed at a leading AI Lab as part of their extended workforce.

2. Key Responsibilities

• Build and ship full-stack applications, services, and internal tools 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 the surrounding scaffolding: tool interfaces, evaluation harnesses, and telemetry.
• Diagnose and document model and integration failure modes surfaced while building, translating engineering observations into clear written feedback for the research team.
• Prototype quickly against shifting requirements, delivering working increments with limited up-front specification.
• Collaborate with the engineering manager and other engineers to maintain consistency in code quality, architecture, and technical documentation.

3. Core Qualifications

this cohort is intentionally staffed across multiple language ecosystems.

• 6+ years of dedicated professional experience building and shipping production software at a recognized, top-tier organization, including ownership of systems end to end.
• Deep production experience in at least one of Python, Java, Rust, C#, or C++, plus demonstrated delivery in a second language across a different ecosystem
• Hands-on ownership across the stack: backend service and API design, a modern front-end framework (React or equivalent), data modelling, and cloud deployment and operations.
• Demonstrated ability to onboard onto an unfamiliar codebase and deliver working code quickly with minimal ramp-up.
• Demonstrable career progression.
• Ability to engage reliably for at least 40 hours/week during weekdays.
• Strong written communication skills and the ability to explain complex technical decisions clearly.

About Cincinnatus LLC: Cincinnatus LLC is an enterprise staffing company that partners with leading technology companies to source and employ highly skilled professionals for contingent and contract-based opportunities. Cincinnatus serves as the employer of record for these engagements, providing W-2 employment, payroll, benefits, and compliance, while placing employees directly within client teams to work on high-impact initiatives.

Equal Employment Opportunity: Cincinnatus is proud to be an Equal Employment Opportunity employer. We do not discriminate based upon race, religion, color, national origin, sex (including pregnancy, childbirth, reproductive health decisions, or related medical conditions), sexual orientation, gender identity, gender expression, age, status as a protected veteran, status as an individual with a disability, genetic information, political views or activity, or any other legally protected characteristic.

AI evaluation Clinical reasoning Python Research

Who this role may fit

This opportunity may suit professionals with relevant experience in AI evaluation, Clinical reasoning, Python, Research.

Compensation context

The listing states $90 - $110 / hour.

• You can show recent, specific work involving AI evaluation, Clinical reasoning, Python.
• The listed commitment of 40 hours/week fits your schedule.
• You can communicate your reasoning clearly in the application language.
• You are comfortable with project availability and hours varying over time.