Fullstack Engineer, RL Environments

ABOUT MERCOR Mercor's mission is to organize human intelligence to power the AI economy. We partner with leading AI labs and enterprises to provide the human intelligence essential to AI development. Our vast talent network trains frontier AI models in the same way teachers teach students: by sharing knowledge, experience, and context that can't be captured in code alone. Today, more than 30,000 experts in our network collectively earn over $3 million a day. Mercor is creating a new category of work where expertise powers AI advancement. Achieving this requires an ambitious, fast-paced and deeply committed team. You’ll work alongside researchers, operators, and AI companies at the forefront of shaping the systems that are redefining society. Mercor is a profitable Series C company valued at $10 billion. We work in-person five days a week in our San Francisco, NYC, or London offices. ABOUT THE ROLE Studio is one of Mercor's highest-priority initiatives. It is the internal platform that powers every workflow our teams use to generate, manage, quality-review, and deliver data to the world's leading AI labs — and its quality directly shapes the frontier models that billions of people interact with. As a Senior Fullstack Software Engineer on the Studio Experience team, you'll own the Studio user journeys end-to-end: the React frontend used daily by thousands of expert contributors and internal Strategic Project Leads, and the backend services powering data pipelines and delivery of outputs to customers. You'll also build and maintain the foundational layer that Mercor depends on to rapidly deploy new data types and task formats across the company. Four distinct stakeholders — AI labs, SPLs, expert contributors, and engineers— rely on what you build. This is a role for someone who cares equally about engineering craft and product impact: shipping scalable, reliable systems and intuitive interfaces that make everyone who touches Studio faster and more effective. YOU WILL - Own the Studio platform across the full stack — from contributor-facing and operator-facing React interfaces to the backend APIs and pipelines driving data ingestion, QA review, and AI lab delivery. - Lead engineering best practices across the team, setting the bar for frontend architecture, component design, and performance, and establishing patterns that others can build on reliably. - Build the foundational layer that other teams depend on to support new data types, task formats, and customer configurations quickly and without rework. - Ship high-leverage product features that improve throughput and quality across our core data generation and delivery pipelines. - Translate ambiguous requirements into well-scoped technical solutions through close collaboration with Applied AI researchers, product, design, and operations. WHAT WE'RE LOOKING FOR - 5+ years of fullstack engineering experience building and shipping production software. - Deep proficiency in JavaScript/TypeScript (React + Next.js) and a strong grasp of frontend architecture, state management, and design patterns. - Solid backend experience in Python and/or Node.js — experience designing and building relational databases, REST APIs, and async task infrastructure. - Strong design sense and empathy for end-users; you hold a high bar for usability. - Experience with complex, high-throughput systems — pipelines, large data volumes, or multi-tenant architectures. - High ownership mindset; able to navigate ambiguity and drive projects from design through delivery. - Strong communication skills and ability to articulate technical and product tradeoffs clearly. NICE-TO-HAVES - Experience building tooling for data labeling, annotation, or human-in-the-loop AI workflows. - Background in design systems, developer-facing APIs, or internal platform engineering. - Exposure to AI tools, LLM-powered products, or real-time data and visualization. - Experience at top-tier tech companies or fast-scaling startups. WHY TH