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

$90–110/hrrate as listed

Build production-grade full-stack software against pre-release frontier models, then document where the models and integrations break. It is a full-time, 40 hr/week W-2 engagement through Cincinnatus LLC placed inside a leading AI lab's GenAI team, with pay observed in the $90–110/hr range.

Summary, eligibility guidance and screening preparation are prepared by Sidequest from the platform's posting. Check the source listing before applying.

What the work actually involves

This is engineering work first and evaluation work second. You are handed shifting requirements and early access to model APIs, and you ship real applications, services, and internal tools on top of them — backend and API design, a React-or-equivalent front end, data modelling, and cloud deployment. Around that you build the scaffolding the research team needs: tool interfaces, evaluation harnesses, telemetry. The valuable output is twofold: working code, and precise written accounts of how the model failed while you were building with it — where tool calls degraded, where long-context reasoning broke, where the API contract did not survive contact with production.

The cohort is staffed deliberately across language ecosystems. Deep production ownership in at least one of Python, Java, Rust, C#, or C++ is the bar, plus real delivery in a second language from a different ecosystem. Expect to work directly with the AI lab's engineering manager, onboard onto unfamiliar codebases fast, and produce working increments without much up-front specification.

What the screening measures

Mercor's screen is AI-led and drills on verifiable specifics. Expect follow-ups that push past framework names into architecture decisions, tradeoffs you rejected, incident history, and what you personally owned versus what your team owned. Also assessed:

Breadth claims held up under probing — a second language you can genuinely defend, not one you touched once
Ramp-up evidence: a concrete story of landing meaningful code in an unfamiliar repo within days
Written communication, since failure-mode reports are a primary deliverable
Career progression at recognized engineering organizations, 6+ years of shipped production work

Logistics

Remote, weekday-aligned, and genuinely full-time — 40 hours per week with reliable overlap for collaboration with the engineering manager. This is W-2 employment with Cincinnatus LLC acting as employer of record, including payroll, benefits, and compliance, with placement inside the client lab's extended workforce. Pay in the $90–110/hr band reflects observed rates for this cohort and is not guaranteed; final rate depends on language depth, seniority, and the lab's staffing needs.

What they look for

6+ years shipping production software with end-to-end system ownership
Deep production depth in one of Python, Java, Rust, C#, or C++
Demonstrated delivery in a second language from a different ecosystem
Full-stack ownership: API design, React or equivalent, data modelling, cloud deployment
Fast onboarding onto unfamiliar codebases with minimal specification
Strong technical writing for failure-mode reports and documentation

Before you apply

Would you pass this screen?

Drawn from what this listing actually requires. Answered in your browser — nothing is sent to us, and we do not store your answers.

Have you spent at least six years of your professional career building and shipping production software at a recognized, top-tier technology organization (e.g., FAANG, unicorn startup, major tech company, or established enterprise software firm)?
Production experience in 6+ years at top-tier organization · required
Have you shipped production code (systems running in real user-facing or internal service environments) in at least one of Python, Java, Rust, C#, or C++?
Hands-on production depth in Python, Java, Rust, C#, or C++ · required
Have you owned systems across the full stack: backend service and API design, a modern frontend framework (React or equivalent), data modelling, and cloud deployment and operations—either in a single system or across the roles and projects in your career?
Full-stack delivery: backend, frontend, data, and cloud · required
Have you shipped production code in at least two different programming languages from different language families (e.g., Python and Java; Rust and C#; C++ and TypeScript)?
Multi-language production experience · required
Are you able to commit to and maintain 40 hours per week during US business hours (weekdays) for the duration of this role?
40 hours/week weekday availability · required
Can you point to clear evidence of career progression—increased scope, responsibility, or technical depth—across your professional history?
Demonstrated career progression · preferred

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Included with this listing

Interview prep — 10 questions

Matched to what this platform's screening actually measures. Answer each out loud in 60–90 seconds: claim → concrete example → implication.

What it tests: Whether you have genuine full-stack ownership experience (not just feature work in a service written by someone else) and whether you can articulate clear tradeoffs in technology selection and deployment.
A strong answer: Describe a specific system you architected and shipped, name the languages/frameworks you used for backend and frontend, explain why those choices made sense for the constraints (scale, latency, team size), and give a concrete metric or user outcome that proved it worked.
Where people lose it: Naming technologies without explaining why you chose them, dwelling on debugging rather than design decisions, claiming ownership of work that was really driven by someone else, or describing a proof-of-concept instead of something that had to scale or stay up.