Senior Fullstack Engineer, AI Observability & Evals Platform

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 onsite 5 days/week in Boston, MA We're looking for a Senior Fullstack Engineer to work on LangSmith. In this role, you'll have the opportunity to shape the technical direction of our platform while working closely with our enterprise customers, developer end-users, and cross functional internal stakeholders. WHAT YOU WILL DO - Lead the technical architecture and implementation of key product features for LangSmith, working across our entire Go, Python, and Typescript stack. - Collaborate closely with product and design teams to iterate on new features. - Help drive aggressive project timelines while ensuring high engineering standards are being met. - Lead by example in writing clean, maintainable, and well-tested code. WHAT YOU BRING - 5+ years of experience in software engineering working on complex platform products - Fullstack engineering experience with Go or Python on the backend and React + Typescript on the frontend. - Strong understanding of database systems, particularly Postgres and Redis - Experience designing and scaling APIs, preferably in a high-performance, data-intensive application - A “get stuff done” attitude - comfortable shipping fast and iterating based on user feedback - Strong communicator with the ability to collaborate closely with various internal stakeholders and engage directly with our top-tier customers - Strong ownership mindset - Bonus: Experience with AI/LLM-powered applications, developer tools, or observability platforms Compensation - Annual salary range: $175,000-$240,000 USD 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.