Senior Backend Software Engineer, AI Observability & Evals Platform; LangSmith

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.

With $125M raised at Series B from IVP, Sequoia, Benchmark, Capital

G, 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.

In person 5 days/week in San Francisco, Boston, MA, New York.

We are looking for a Senior Backend Engineer to join us. In this role you will be building the backend systems that power Lang Chain’s observability and evals platform. You will work on the core services that allow developers to monitor and evaluate their AI applications le the focus is on backend feature development, familiarity with fullstack or frontend engineering, performance tuning, and debugging production issues would be extremely valuable.

• Design, develop, and maintain backend services and APIs to support Lang Smith’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.

• 5+ years of professional experience in backend engineering working on highly complex products
• Proficiency in one or more backend languages/frameworks, ideally Python or Go
• Strong understanding of API design and building reliable data services.
• Experience with high-throughput or 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)
• Strong communication skills, with the ability to collaborate cross-functionally
• Customer centricity and ownership mentality

Compensation

Annual salary range: $175,000—$240,000

Compensation Philosophy:

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.