Senior Fullstack Engineer, AI Observability & Evals Platform

About Us

At Lang Chain, 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.

At Lang Chain, 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 h $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.

Lang Chain is a place where your contributions can shape how this technology shows up in the real world. Today, our platform includes Lang Smith (Observability, Evaluation, Deployment, Fleet, and Sandboxes), our open source frameworks (Lang Chain, Lang Graph, and Deep Agents), and the newly launched Lang Smith Engine for autonomous agent improvement. We have 100M+ monthly open source downloads, 6,000+ active Lang Smith customers, and 5 of the Fortune 10 use Lang Smith in production (+ 35% of the Fortune 500 overall), including teams at Klarna, Clay, Coinbase, Workday, Lyft, Cloudflare, Harvey, Rippling, Vanta, Linked In, , Nvidia, and Bridgewater.

The Lang Smith team owns and builds Lang Chain'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 Lang Smith end-to-end. If you want to define what great AI observability looks like at production scale, this is where that work gets done.

This role is onsite 5 days/week in Boston, MA.

We're looking for a Senior Fullstack Engineer to work on Lang Smith. 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.

• Lead the technical architecture and implementation of key product features for Lang Smith, 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.

• 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

• Annual salary range: $175,000-$240,000 USD

We offer competitive compensation that includes base salary, variable compensation for relevant roles, meaningful equity, benefits, and perks. Actual compensation and offerings will vary based on role, level, and location. Team members in the EU, UK, and APAC receive locally competitive benefits aligned with regional norms and regulations.

Benefits include medical, dental, and vision coverage, flexible vacation, a 401(k) plan, meals on in-office days in the US and more.