Principal Software Engineer, AI Observability & Evals Platform

About the Team

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, 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.

We’re looking for a Principal/Lead level Software Engineer to join the Lang Smith 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.

• Lead architectural decisions across our Go, Python, and Type Script 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.

• 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.

• 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.

• 10+ years of professional experience in backend or full‑stack engineering on highly complex, production systems.
• Strong programming skills across multiple parts of the stack: backend (Python and/or Go) and frontend (Type Script, React, or similar).
• Demonstrated experience making and owning architectural decisions, including tradeoffs around data systems, APIs, and service reliability.
• Experience with high‑throughput or mission‑critical systems, and a proven ability to optimize for performance and reliability.
• Depth in operationalizing technical work — you’ve taken systems from prototype to production and kept them running well at scale.
• Demonstrated track record of mentoring engineers and raising the technical quality of a team, not just the codebase.
• Strong communication skills and comfort operating cross‑functionally with product, design, and engineering leadership.
• Customer centricity and an ownership mentality — you care how the product lands, not just how the code reads.
• You exemplify our operating principles.

• Experience with database systems (Postgres, Redis, Click House) and cloud platforms (AWS, GCP, or Azure).
• Familiarity with observability tooling, evaluation frameworks, or AI/LLM infrastructure.

Salary Range: $230,000 - $270,000

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.