Senior Backend Engineer (IAM and Billing)

About Langfuse

Open Source LLM Engineering Platform that helps teams build useful AI applications via tracing, evaluation, and prompt management. We are now part of ClickHouse.

We are building the "Datadog" of this category; model capabilities continue to improve, but building useful applications is really hard, both in startups and enterprises.

We are the largest open source solution in this category, trusted by 19 of the Fortune 50, >2k customers, >26M monthly SDK downloads, >6M Docker pulls.

We joined ClickHouse in January 2026 because LLM observability is fundamentally a data problem and Langfuse already ran on ClickHouse. 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.

Previously backed by Y Combinator, Lightspeed, and General Catalyst.

We are a small, engineering‐heavy, experienced team in Berlin and San Francisco. We are also hiring for engineering in EU timezones and expect one week per month in our Berlin office.

IAM & Billing Role Overview

Every API call, dashboard load, team invitation, and usage‐based invoice flow through the systems you will own. Authentication, authorization, and billing are shared platform components that every product team depends on.

This role has unusual scope: design the identity and access model to let Fortune 50 companies manage hundreds of users across projects and environments with fine‐grained permissions, build billing infrastructure that translates billions of trace events into accurate real‐time usage metering and invoicing, and ensure the platform works seamlessly for both Langfuse Cloud and self‐hosted deployments.

The stakes are high – auth errors break the platform; billing errors break the business. You will own these critical components end‐to‐end, from design through production.

Key Responsibilities

• Own authentication and identity: build and evolve how users and API keys authenticate with Langfuse, supporting SSO/SAML, OAuth, API key management, and session handling.


• Design fine‐grained authorization: architect the permission model for enterprises with projects, roles, and scoped access controls; build RBAC (and eventually ABAC) layer that product engineers rely on.


• Build usage‐based billing infrastructure: own the metering pipeline that counts events accurately at massive scale, integrate with payment providers, and generate trustworthy invoices; handle plan management, entitlements, and self‐serve upgrade flows.


• Create shared platform APIs: design clean, well‐documented internal APIs and abstractions that let product engineers ship quickly without worrying about permission checks or billing edge cases.


• Support self‐hosted flexibility: ensure the auth layer integrates with enterprise identity stacks (LDAP, OIDC, SAML).


• Scale for enterprise adoption: prepare for audit logging, compliance requirements, multi‐tenant isolation, and complex pricing models as demand grows.

Qualifications

• Strong backend engineer focused on secure, reliable platform systems.


• 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.


• Good understanding of security, edge cases, and failure modes, especially in multi‐tenant environments.


• Strong organizational skills and clear API design principles.


• Comfortable reading and writing TypeScript and SQL.


• Interest in open source software and empathy for self‐hosted operators.


• Thrives in a small, accountable team where output is visible and matters.


• CS or quantitative degree preferred.

Bonus Points

• 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) related to auth and data access.


• Former founder.

Process

We can run the full process to your offer letter in less than 7 days.

Tech Stack

TypeScript monorepo: Next.js frontend, Express workers for background jobs, PostgreSQL for transactional data, ClickHouse for tracing at scale, S3 for file storage, Redis for queues and caching.

How We Ship

• Ownership: identify what to build, propose solutions (RFCs), ship them.


• Collaboration: whiteboard sessions, shared discussions.


• Schedule: two recurring meetings a week (Monday priorities, Friday demo).


• Code reviews: mentorship oriented; new joiners get all PRs reviewed.


• AI adoption: use AI tools in workflows to improve user experience.

Why Langfuse (now part of ClickHouse)

• Front‐line role in the AI revolution, partnering with engineering teams that define future tech.


• Open‐source devtools company that ships daily, focuses on developer experience, reliability, and performance.


• Public credit: your work appears on changelog posts and launch videos.


• Hard engineering problems: building helpful features, SDKs, visualization, efficient rendering, data ingestion at terabyte scale.


• Learning: work closely with ClickHouse team and continue to grow in a high‐growth environment.


• Community engagement: help guide product direction via Slack or GitHub discussions.


• Continuous learning: stay ahead of the rapidly evolving AI space.

Compensation Range: €90K - €160K