Senior Backend Software Engineer, Observability & Evals Platform; LangSmith

Senior Backend Software Engineer, Observability & Evals Platform (Lang Smith)

Apply for the Senior Backend Software Engineer, Observability & Evals Platform (Lang Smith) role at Lang Chain.

Location:

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

About Lang Chain: At Lang Chain, our mission is to make intelligent agents ubiquitous. We provide the agent engineering platform and open source frameworks developers need to ship reliable agents fast. Lang Chain’s open‑source frameworks, Lang Chain and Lang Graph, see over 90+ million downloads per month and help developers build agents with speed and granular control. Lang Smith offers observability, evaluation, and deployment for rapid iteration, enabling teams to transform LLM systems into dependable production experiences.

Lang Chain is trusted by millions of developers worldwide and powers AI teams at companies like Replit, Clay, Cloudflare, Harvey, Rippling, Vanta, Workday, and more.

We are looking for a Senior Backend Engineer to build the backend systems that power Lang Chain’s observability and evals platform. You will work on core services that allow developers to monitor and evaluate their AI applications le the focus is on backend feature development, familiarity with full‑stack 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.
• 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.

• Competitive compensation that includes base salary, meaningful equity, and benefits such as health and dental coverage, flexible vacation, a 401(k) plan, and life insurance. Actual compensation will vary based on role, level, and location. For team members in the EU and UK, we provide locally competitive benefits aligned with regional norms and regulations.
• Annual salary range: $170,000 – $195,000.

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