Principal Software Engineer, AI Observability & Evals Platform

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, they own this end-to-end. If you want to help define what great AI observability looks like at production scale, this is where that work gets done. ABOUT THE ROLE We're looking for a Principal/Lead level Software Engineer to join the LangSmith team and help drive the technical direction of the platform. You'll build across the full stack from backend services and APIs to frontend product surfaces, and you'll play a central role in shaping how we build: setting engineering standards, mentoring engineers across the team, and making architectural decisions that hold up as we scale. If you're energized by both hands-on engineering and the multiplier effect of leveling up those around you, this role is built for that. Location: This role can be based in our Boston, San Francisco, or NYC office. WHAT YOU'LL DO DRIVE TECHNICAL DIRECTION - Lead architectural decisions across our Go, Python, and TypeScript stack, ensuring systems are performant, maintainable, and built to scale - Work across the full stack, owning features end-to-end from backend services and APIs through to frontend product experiences - Drive tracing, monitoring, and evaluation workflows at scale, with a focus on reliability and query performance across high-volume data - Help shape the product roadmap by partnering closely with product and design — not just executing on it RAISE THE BAR FOR THE TEAM - Set engineering standards for the team: define patterns, lead code reviews, and establish the foundations others build on - Mentor and grow engineers at all levels through code review, design feedback, pairing, and ongoing technical guidance - Drive projects from ambiguity to delivery while maintaining high engineering standards and aggressive timelines OWN RELIABILITY AND QUALITY - Troubleshoot and resolve production issues with a root-cause mindset, and implement durable fixes - Ensure system reliability through strong testing, monitoring, and alerting practices - Create and maintain technical documentation, including system design docs and API references WHAT YOU'LL BRING - 10+ years of professional experience in backend or fullstack engineering on highly complex, production systems - Strong programming skills across multiple parts of the stack: backend (Python and/or Go) and frontend (TypeScript, React, or similar) - Demonstrated experience making and owning architectural decisions, including tradeoffs around data systems, APIs, and service reliability - Experien