Lead Full-Stack Engineer
We're looking for an ambitious, hands-on Lead Full-Stack Developer who builds with AI coding agents every day and knows how to make that fast and reliable.
Our platform builds and quality-checks reinforcement-learning tasks for frontier AI labs: authoring, review, automated QA in cloud sandboxes, and customer acceptance. It's built quickly by a small team working heavily with AI agents. This is an opportunity to own how we build software: ship features, spot what to improve, deliver our roadmap, and establish engineering practices from scratch. You can then grow into leading the engineering team.
What You'll Do
Ship, constantly: Take feature requests from our researchers, reviewers and operators, and deliver them to production within days, across a FastAPI backend and a Next.js frontend.
Vibe code with discipline: Build with AI coding agents as your main tool, and set the standard for doing it well: clear context, tight scope, tests that mean something, and diffs that get read.
Establish engineering best practices from 0 to 1: Introduce code review, linting, testing and CI gates that make the team safer without slowing it down.
Find what to improve: Spot weak points in the code and product, such as tangled modules, missing tests or slow pages, and fix them incrementally while features keep shipping.
Deliver the plan: Turn our existing roadmap into sequenced, shippable work, and push back with evidence when something should change.
Guard correctness where it matters: Make sure the rules behind reviews, acceptance and payouts are enforced in code and covered by tests.
Shape the future team: Review others' work, mentor, share knowledge, and potentially lead the engineering team as it grows.
What We're Looking For
Proven engineering experience: A track record of shipping production software as a hands-on senior or lead engineer.
AI-native workflow: You build with Claude Code, Cursor, Codex or similar every day, and you have opinions on how to keep agent-written code correct.
Full-stack generalist: Strong Python (FastAPI, SQLAlchemy, asyncio), TypeScript and React (Next.js), and PostgreSQL. Comfortable with any part of the stack on any given day.
Builder mentality: You enjoy creating systems and processes, solving ambiguous problems, and taking ideas all the way to production.
Strong ownership and autonomy: You take responsibility for the things nobody else sees, because you see them. You drive them to measurable results without constant supervision.
Pragmatic quality: You know the difference between practices that protect a team and ceremony that slows it down.
Ambition and drive: A highly motivated, resourceful and results-oriented person who wants to grow quickly, stays hands-on, and is ready to lead a team forward.
We value demonstrated achievements, intellectual curiosity and the ability to execute over years of experience or impressive job titles.
Nice to Have
Experience establishing engineering practices in a startup or high-growth company.
Experience combining hands-on development with tech-lead or team-lead responsibilities.
Experience improving a codebase written largely by AI agents.
Experience building agent tooling: project context files, custom review prompts, MCP servers.
Experience with marketplaces, payouts or review workflows, where correctness carries money.
Exposure to LLM evaluation, reinforcement learning or AI research tooling.
Why Join ARIMLABS?
Build something from scratch: Take ownership of how we build software and set the standards the team grows with.
Exceptional growth opportunities: Join a fast-scaling AI research company at an early stage, grow alongside the business, and potentially lead your own team.
High autonomy: Freedom to experiment, make decisions and ship without unnecessary bureaucracy.
Work with exceptional people: Collaborate with highly skilled researchers, engineers and domain experts working on challenging problems at the frontier of artificial intelligence.
Exposure to frontier AI: Work with frontier models every day, both in your own workflow and in the product you build.
Entrepreneurial environment: Work in a company that values initiative, speed, ownership and ambitious thinking.
Career flexibility: Shape your long-term career toward engineering leadership or deep technical ownership as the organization expands.
Compensation & Working Conditions
Engagement: B2B contract.
Time off: 24 days of paid time off annually.
Autonomy: Significant freedom to organize your work and establish effective processes.