engineering
Posted Apr 17Senior Backend Engineer (IAM and Billing)
at Langfuse
GermanyRemote
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Responsibilities
- Design fine-grained authorization: You'll architect the permission model that lets enterprises manage complex organizational structures — projects, roles, and scoped access controls.
- Build usage-based billing infrastructure: Langfuse bills based on trace volume.
- Create shared platform APIs: Auth and billing touch every surface of the product.
- Support self-hosted flexibility: Many teams run Langfuse on their own infrastructure with their own identity providers.
Requirements
- ABOUT LANGFUSE Open Source LLM Engineering Platform that helps teams build useful AI applications via tracing, evaluation, and prompt management (mission https://tracking.us.nylas.com/l/6d586a21a6fc4e1a8aacc7eb75882b72/0/82383757e54352130f65066e1b2fc4708aacab7897561bcb8000fe4c8a9c6a21?cache_buster=1761124921, product https://tracking.us.nylas.com/l/6d586a21a6fc4e1a8aacc7eb75882b72/1/b9fba3a93b6ffcc0f99ecda62767a17cc437fe8fe0b16181d1c43c1391212e3d?cache_buster=1761124921).
- Largest open source solution in this category: trusted by 19 of the Fortune 50, >2k customers, >26M monthly SDK downloads, >6M Docker pulls.
- Together we can move faster on product while staying true to open source and self-hosting, and join forces on GTM and sales to accelerate revenue.
- Few backend roles offer this combination: mission-critical scope, open source visibility, and direct impact on how thousands of companies adopt and pay for AI tooling.
- YOU WILL GROW AT LANGFUSE BY Own authentication and identity: You'll build and evolve how users and API keys authenticate with Langfuse — supporting SSO/SAML, OAuth, API key management, and session handling.
- You'll build the RBAC (and eventually ABAC) layer that product engineers rely on when shipping every new feature.
- You'll make sure our auth layer integrates cleanly with enterprise identity stacks (LDAP, OIDC, SAML).
- Experience building authentication and authorization systems — SSO/SAML, OAuth, RBAC, API key management - Familiarity with billing or payments infrastructure — usage-based metering, payment provider integrations (Stripe or similar), entitlements - You think carefully about security, edge cases, and failure modes — especially in multi-tenant environments - You organize yourself.
- Experience building multi-tenant SaaS platforms with enterprise identity
- requirements - Background in usage-based billing systems or fintech infrastructure - Familiarity with compliance frameworks (SOC 2, GDPR) as they relate to auth and data access - Former founder PROCESS We can run the full process to your offer letter in less than 7 days (hiring process https://langfuse.com/handbook/how-we-hire/hiring-process).
- TECH STACK We run a TypeScript monorepo: 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.
- New joiners get all PRs reviewed to learn the codebase, patterns, and how the systems work (onboarding guide https://langfuse.com/handbook/product-engineering/how-we-work/onboarding). - We use AI as much as possible in our workflows to make our users happy.
- We encourage everyone to experiment with new tooling and AI workflows.
- WHY LANGFUSE (NOW PART OF CLICKHOUSE) - This role puts you at the forefront of the AI revolution, partnering with engineering teams who are building the technology that will define the next decade(s). - This is an open-source devtools company.
- You’ll own the full delivery end to end. - We're solving hard engineering problems: figuring out which features actually help users improve AI product performance, building SDKs developers love, visualizing data-rich traces, rendering massive LLM prompts and completions efficiently in the UI, and processing terabytes of data per day through our ingestion pipeline. - You'll work closely with the ClickHouse team and learn how they build a world-class infrastructure company.
- The AI space develops at breakneck speed and our customers are at the forefront.
Benefits
- You have strong opinions about API design, system boundaries, and how to ship shared infrastructure safely - Comfortable reading and writing TypeScript (our backend) and SQL - Interest in open source software and empathy for self-hosted operators who need to integrate with their own identity stacks - Thrives in a small, accountable team where your output is visible and matters - CS or quantitative degree preferred Bonus points: -
Contact
- We are also hiring for engineering in EU timezones and expect one week per month in our Berlin office (how we work https://langfuse.com/handbook/how-we-work/principles).
- You should be familiar with a good chunk of this, but we trust you'll pick up the rest quickly (Stack https://langfuse.com/handbook/product-engineering/tech-stack, Architecture https://langfuse.com/handbook/product-engineering/architecture).
- HOW WE SHIP Link to handbook https://langfuse.com/handbook/how-we-work/principles - We trust you to take ownership (ownership overview https://langfuse.com/handbook/how-we-work/ownership) for your area.
- You'll appear on changelog posts https://langfuse.com/changelog for the features you build, and during launch weeks, you'll produce videos https://langfuse.com/blog/2025-10-29-launch-week-4 to announce what you've shipped to the community.
- We're in a period of strong growth: Langfuse is growing organically and accelerating through ClickHouse's GTM. (Why we joined ClickHouse https://langfuse.com/blog/joining-clickhouse) - If you wonder what to build next, our users are a Slack message or a Github discussions post away. - You’re on a continuous learning journey.
Additional details
- We're building the "Datadog" of this category; model capabilities continue to improve, but building useful applications is really hard, both in startups and enterprises.
- Previously backed by Y Combinator, Lightspeed, and General Catalyst.
- We're a small, engineering-heavy, and experienced team in Berlin and San Francisco.
- WHY IAM & BILLING AT LANGFUSE Your work will be the foundation everything else is built on.
- Every API call, every dashboard load, every team invitation, every usage-based invoice — they all flow through the systems you'll own.
- Authentication, authorization, and billing aren't features at Langfuse; they're the shared platform that every product team depends on.
- You'll design the identity and access model that lets Fortune 50 companies manage hundreds of users across projects and environments with fine-grained permissions.
- You'll build the billing infrastructure that translates billions of trace events into accurate, real-time usage metering and invoicing.
- And you'll do it all in a way that works seamlessly for both Langfuse Cloud and self-hosted deployments.
- The stakes are high — get auth wrong and nothing works; get billing wrong and the business doesn't work — but that's exactly what makes this role rewarding.