Fullstack Software Engineer, Agent Platform

About Mercor Mercor's mission is to organize human intelligence to power the AI economy. We're a leading AI data company, building the layer between human expertise and frontier models. Millions of domain experts on the platform are paid over $4 million per day to train frontier AI models. Mercor's APEX benchmark family measures AI's real-world impact on professional work. Mercor Enterprise brings this same infrastructure to Fortune 500 companies: helping companies capture how their best people actually work, translating that expertise directly back into agents. 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 Our agent platform is the core system Mercor uses to build, run, and showcase AI agents — the same platform our teams rely on internally every day and the one we demo live on customer calls. It is simultaneously our internal workbench and our external storefront. As a Full Stack Software Engineer on the Agent Platform team, you'll own these journeys end-to-end: the React frontend people interact with and the backend services that orchestrate agents, data, and integrations. You'll be directly responsible for the enablement of hundreds of internal users who depend on the platform daily, and dozens of enterprise clients who run on it in production. Because what you build is used in-house and demoed to customers, it has to be both genuinely powerful and demo-ready polished. 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 the platform faster and more effective. YOU WILL - Own the agent platform across the full stack — from the internal- and client-facing React interfaces to the backend APIs and services orchestrating agents, workflows, and integrations. - Enable hundreds of internal users and dozens of enterprise clients — ship the features, reliability, and polish that make the platform their daily driver and a confident live demo. - Build the foundational layer other teams depend on to stand up new agent use cases, task formats, and client configurations quickly and without rework. - Ship high-leverage product features that raise both internal productivity and the customer-facing quality of the platform. - Translate ambiguous requirements into well-scoped technical solutions through close collaboration with Applied AI researchers, product, design, and operations. WHAT WE'RE LOOKING FOR - 2+ 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 — 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 agent frameworks, LLM-powered products, or human-in-the-loop AI workflows. - Background in design systems, developer-facing APIs, or internal platform engineering. - Exposure to AI tools, real-time data, or data visualization. - Experience at top-tier tech companies or fast-scaling startups. WHY THIS ROLE MATTERS - The platform you build is Mercor's core agent product — run internally and shown to every enterprise client. - The systems you ship will be used daily by hundreds of internal users and dozens of enterprise clients. - You'll help define how new agent use cases are built, delivered, and demonstrated at Mercor. - Your work directly shapes both how Mercor works and how customers experience us. BENEFITS - Bi-annual performance bonus structure - Generous equity grant vested over 4 years - Up to $15k Relocation