Senior Software Engineer, SDK

📍 Germany
📍 Spain
📍 France
📍 Italy
📍 Netherlands
📍 Portugal

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 API @ 4 GenAI Go Java LLM @ 4 LangChain Machine Learning @ 3 Observability @ 4 OpenTelemetry @ 4 Profiling @ 7 Python @ 4 TypeScript @ 4

Details

The SDK team owns Langfuse's open-source Python and TypeScript SDKs, which are built on OpenTelemetry and downloaded more than 26 million times per month. The role focuses on reliability, performance, developer experience, API design, integrations, and documentation for developers building LLM applications.

Responsibilities

Own the Python and TypeScript SDKs, including reliability, performance, developer experience, error handling, batching, asynchronous flushing, and graceful degradation.
Design developer-friendly APIs, including function naming, parameter structures, documentation, versioning, and migration paths.
Maintain integrations with 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 ecosystem evolves.
Maintain and document the OpenTelemetry Protocol (OTLP) endpoint and support Langfuse features across languages with OpenTelemetry SDKs, including Java and Go.
Collaborate with the OpenTelemetry community on GenAI conventions.
Own SDK documentation, integration guides, and migration paths.
Manage projects independently and make decisions about what to build and how to ship it.

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 profiling, benchmarking, and minimizing CPU and memory overhead in hot paths.
Experience with versioning, backward compatibility, and migration paths.
Interest in open-source software and enthusiasm for helping developers solve integration challenges.
Ability to thrive in a small, accountable team.
A computer science or quantitative degree is preferred.

Bonus Qualifications

Experience with OpenTelemetry internals or observability instrumentation.
Former founder or early-stage startup experience.
Contributions to popular open-source SDKs or developer tools.
Machine learning or artificial intelligence experience, or familiarity with the LLM framework ecosystem.

Benefits

Flexible, remote-friendly work environment in a globally distributed company operating in more than 25 countries.
Employer healthcare contributions.
Company stock options for new team members.
Flexible time off in the United States and generous entitlement in other countries.
USD 500 home-office setup allowance for remote employees.
Company-wide global gatherings and offsites.
Equal employment opportunities and a non-discrimination policy.