Backend Software Engineer (Senior) at Mercor

About MercorMercor is training models that predict how well someone will perform on a job better than a human can. We use our platform to source, vet, and onboard expert contractors who help train AI models in a wide variety of domains. Our technology is so effective it’s used by all of the top 5 AI labs.We scaled from $1–500M in revenue run rate in the last 17 months, making us the fastest growing company in the world. Our growth is accelerating: 11% week-over-week in July, 18% in August, and 19% in September. The team is small, profitable, and growing as fast as we can hire exceptional people.About the RoleAs a Senior Software Engineer at Mercor, you’ll take end-to-end ownership of complex projects that power the workflows of the world’s leading AI companies. You’ll architect and scale distributed systems, mentor other engineers, and set technical direction for high-impact initiatives. This role goes beyond coding: you’ll help shape engineering culture, influence product decisions, and ensure our systems scale in lockstep with our hyper-growth.What You’ll DoDesign, build, and scale production-grade backend APIs, services, and infrastructure.Take ownership of system design and architecture decisions that impact core workflows.Mentor and support junior engineers through code reviews, pair programming, and design discussions.Partner with Product and Design to deliver features quickly without sacrificing quality or scalability.Anticipate technical bottlenecks, propose solutions, and drive initiatives that increase reliability.Contribute to the systems that enable OpenAI, Anthropic, Google, and others to train and evaluate their models.What We’re Looking ForStrong coding fundamentals in Python (our primary backend), though interviews are language-agnostic.Deep understanding of distributed systems, scalability challenges, and system design.Experience shipping production systems at scale in high-growth or high-stakes environments.Ability to reason about trade-offs and make decisions balancing speed and reliability.Strong communication skills with an ability to align technical and business goals.Bias toward ownership, curiosity, and delivering simple solutions to complex problems.Why MercorImpact: Your work powers how the world’s leading AI labs train and test their models.Learning: Get early insights into frontier model capabilities months before the market.Growth: Work on both infrastructure and research-adjacent projects with fast paths to ownership.