Senior Backend Software Engineer, AI Observability & Evals Platform (LangSmith)

Location: Boston, MA; New York, NY Workplace: OnSite ABOUT US At LangChain, our mission is to make intelligent agents ubiquitous. We build the foundation for agent engineering in the real world, helping developers move from prototypes to production-ready AI agents that teams can rely on. We began as widely adopted open-source tools and have grown to also offer a platform for building, evaluating, deploying, and operating agents at scale. With $125M raised at Series B from IVP, Sequoia, Benchmark, CapitalG, and Sapphire Ventures, we’re at a stage where we’re continuing to develop new products, growth is accelerating, and all team members have meaningful impact on what we build and how we work together. LangChain is a place where your contributions can shape how this technology shows up in the real world. Today, our platform includes LangSmith (Observability, Evaluation, Deployment, Fleet, and Sandboxes), our open source frameworks (LangChain, LangGraph, and Deep Agents), and the newly launched LangSmith Engine for autonomous agent improvement. We have 100M+ monthly open source downloads, 6,000+ active LangSmith customers, and 5 of the Fortune 10 use LangSmith in production (+ 35% of the Fortune 500 overall), including teams at Klarna, Clay, Coinbase, Workday, Lyft, Cloudflare, Harvey, Rippling, Vanta, LinkedIn, Monday.com, Nvidia, and Bridgewater. ABOUT THE TEAM The LangSmith team owns and builds LangChain's core platform for observability, evaluation, and production reliability of AI systems. From tracing and annotation to run rules, evaluations, and beyond, this team owns LangSmith end-to-end. If you want to define what great AI observability looks like at production scale, this is where that work gets done. ABOUT THE ROLE This role is based onsite in Boston, MA. We are looking for a Senior Backend Engineer to join our growing engineering team in Boston. In this role you will be building the backend systems that power LangSmith, LangChain’s observability and evals platform. You will work on the core services that allow our customer's developer teams to monitor and evaluate their AI applications at scale. While the focus is on backend feature development, familiarity with fullstack or frontend engineering, performance tuning, and debugging production issues would be valuable. WHAT YOU'LL DO: - Design, develop, and maintain backend services and APIs to support LangSmith’s tracing, monitoring, and evaluation workflows. - Collaborate on architectural decisions to ensure systems are performant and maintainable. - Optimize storage and query performance for high-volume observability and evaluation data. - Ensure system reliability through strong testing, monitoring, and alerting practices. - Troubleshoot and resolve production issues, performing root-cause analysis and implementing long-term fixes. - Create and maintain technical documentation, including system design and API references. - Work closely with full-stack engineers, product managers, and product designers on rolling out new features. WHAT YOU'LL BRING: - 4+ years of professional experience in backend engineering working on highly complex products - Proficiency in one or more backend languages/frameworks, ideally Python and/or Go - Strong understanding of API design and building reliable data services. - Experience with high-throughput, mission-critical systems. - Demonstrated ability to optimize backend services for performance and reliability. - Experience with database systems (Postgres, Redis, Clickhouse), and cloud platforms (AWS, GCP, Azure) would be a bonus. - Strong communication skills, with the ability to collaborate cross-functionally. - Customer centricity and ownership mentality Annual salary range: $170,000- $235,000 Compensation Philosophy: We offer competitive compensation that includes base salary, variable compensation for relevant roles, meaningful equity, benefits, and perks. We are hiring for this role across a range of scope, and the compensation band reflects that. Your offer depends on what we learn about your impact, craft, leadership, and communication during the interview process. We will tell you early where you’re tracking and talk comp with you before offer stage. Team members in the EU, UK, and APAC receive locally competitive benefits aligned with regional norms and regulations. BENEFITS Benefits include medical, dental, and vision coverage, flexible vacation, a 401(k) plan, meals on in-office days in the US and more.