Senior Software Engineer (SDK)

📍 Spain
📍 Netherlands
📍 Switzerland
📍 France
📍 United Kingdom
📍 Berlin, Germany
📍 Paris, France
📍 Munich, Germany
📍 Zurich, Switzerland
📍 London, United Kingdom
📍 Germany
📍 San Francisco, United States

EUR 90,000-160,000 per year

SENIOR

✅ Hybrid

Tech Stack
Tag name is followed by "@" symbol and proficiency level value. About proficiency levels:

1-2 — basic awareness. Minimal hands-on experience, and a rudimentary understanding of the technology's purpose;

3-6 — daily use. Comfortable and regular usage, capable of handling common tasks and challenges related to the technology;

7-9 — you are an expert, you can teach others, you know all the pitfalls and tricks;

10 — exceptional knowledge, comprehensive understanding, and adeptness in all aspects of the technology, including advanced problem-solving. Think twice before claiming or demanding such level.

AI @ 4 API @ 4 ClickHouse @ 4 GenAI @ 4 Go @ 4 Hiring @ 4 Java @ 4 LLM @ 4 LangChain @ 4 Machine Learning Next.js @ 4 Observability @ 4 OpenTelemetry @ 4 PostgreSQL @ 4 Profiling @ 7 Python @ 4 Redis @ 4 TypeScript @ 4

Details

Open Source LLM engineering platform (Langfuse, now part of ClickHouse) focused on tracing, evaluation, and prompt management. Small, engineering-heavy team with offices in Berlin and San Francisco and hiring across EU timezones. Role expects a hybrid arrangement with roughly one week per month in the Berlin office.

Responsibilities

Own and maintain Langfuse SDKs (Python and TypeScript) built on OpenTelemetry: reliability, performance, developer experience, error handling, batching, async flushing, and graceful degradation.
Design APIs and developer-facing interfaces: naming, parameter structure, versioning, backwards compatibility, migration paths, and documentation.
Integrate and maintain integrations with major AI frameworks and model providers (40+): OpenAI SDK, Vercel AI SDK, LangChain, LlamaIndex, Pydantic AI, OpenAI Agents, Amazon Bedrock AgentCore, LiveKit, and others; add new integrations as the ecosystem evolves.
Maintain the OpenTelemetry (OTLP) endpoint path to support languages beyond Python/TypeScript (Java, Go, etc.) and collaborate with the OpenTelemetry community on GenAI conventions.
Write and own public SDK documentation, integration guides, and migration paths; ship docs alongside SDK releases.

Requirements

Strong software engineer excited about developer experience, API design, and building code that runs reliably in customers' production systems.
Experience building or maintaining SDKs, client libraries, or developer tools, ideally in Python and/or TypeScript.
Deep understanding of performance: profiling, benchmarking, and minimizing CPU/memory overhead in hot paths.
Ability to manage projects independently: identify what to build, develop conviction, and ship features (RFCs, ownership of area, manage own Linear tasks).
Thoughtful about versioning, backwards compatibility, and migration paths.
Interest in open source and direct engagement with developers about integration challenges.
Comfortable working in a small, accountable team where output is visible and matters.
CS or quantitative degree preferred.

Bonus

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

Tech Stack

TypeScript monorepo (frontend: Next.js; backend/background: Express workers)
PostgreSQL (transactional data), ClickHouse (tracing at scale), S3 (file storage), Redis (queues and caching)
SDKs built on OpenTelemetry; support for many LLM frameworks and model providers

How We Ship / Process

Ownership model: you identify what to build, propose solutions (RFCs), and ship them.
Code reviews used as mentorship; maker schedule and focused asynchronous work.
Hiring process can complete to offer in less than 7 days.