Senior Software Engineer (SDK)

Details

About Langfuse

Langfuse is an open-source LLM engineering platform that helps teams build useful AI applications through tracing, evaluation, and prompt management. Langfuse is now part of ClickHouse. The platform is trusted by 19 of the Fortune 50, has more than 2,000 customers, over 26 million monthly SDK downloads, and more than 6 million Docker pulls.

The team is small, engineering-focused, and based in Berlin and San Francisco, with additional engineering hiring across EU time zones. The role involves spending approximately one week per month in the Berlin office.

Responsibilities

• Own Langfuse's Python and TypeScript SDKs, which are built on OpenTelemetry.
• Ensure SDK reliability, performance, and developer experience across production environments, including serverless functions and long-running agent loops.
• Design developer-friendly APIs, including interfaces, parameter structures, error handling, versioning, breaking-change communication, and documentation.
• Work on SDK capabilities such as batching, asynchronous flushing, graceful degradation, and minimizing CPU and memory impact.
• Maintain integrations with major AI frameworks and model providers, including OpenAI SDK, Vercel AI SDK, LangChain, LlamaIndex, Pydantic AI, OpenAI Agents, CrewAI, Amazon Bedrock AgentCore, and LiveKit.
• Add new integrations as the LLM framework ecosystem evolves.
• Maintain the OpenTelemetry endpoint and ensure it is robust, well documented, and supports Langfuse features.
• Extend language support through OpenTelemetry, including Java and Go, and work with the OpenTelemetry community on GenAI conventions.
• Write and maintain SDK documentation, integration guides, and migration paths.
• Manage projects independently, identify what to build, propose solutions through RFCs, and deliver work end to end.
• Collaborate with the engineering team through whiteboard sessions, code reviews, demos, and regular priority check-ins.

Requirements

• Strong software engineering skills and enthusiasm for developer experience, API design, and reliable production software.
• Experience building or maintaining SDKs, client libraries, or developer tools, ideally in Python and/or TypeScript.
• Deep understanding of performance, including profiling, benchmarking, and minimizing CPU and memory overhead in hot paths.
• Ability to independently manage projects and develop strong conviction about what to build and how to ship it.
• Understanding of versioning, backward compatibility, and migration paths.
• Interest in open-source software and enthusiasm for discussing integration challenges with developers.
• Ability to thrive in a small, accountable engineering team.
• A computer science or quantitative degree is preferred.

Bonus Qualifications

• Experience with OpenTelemetry internals or observability instrumentation.
• Founder or early-stage startup experience.
• Contributions to popular open-source SDKs or developer tools.
• An ML/AI background or familiarity with the LLM framework ecosystem.

Tech Stack

Langfuse operates a TypeScript monorepo with Next.js on the frontend, Express workers for background jobs, PostgreSQL for transactional data, ClickHouse for tracing at scale, S3 for file storage, and Redis for queues and caching. The SDKs use Python, TypeScript, and OpenTelemetry.

Working Practices

• Engineers own their areas, identify and propose work, and ship solutions.
• The team uses a maker schedule with a Monday priority check-in and Friday demo session.
• Code reviews are used for mentorship and onboarding.
• The team experiments with AI tooling and workflows.

Additional Information

The company can run the full hiring process through the offer letter in less than seven days. The role offers the opportunity to work on open-source developer tools, AI engineering, SDK reliability and performance, data-rich traces, and large-scale ingestion systems while collaborating closely with the ClickHouse team.