Langfuse, a scalable open-source LLM observability platform, evolved from a simple prototype to a robust infrastructure capable of processing tens of thousands of events per minute. Originating from the Y Combinator Winter 2023 batch, Langfuse faced several challenges in scaling its architecture, including building a resilient high-throughput ingestion pipeline, optimizing prompt delivery, and ensuring fast analytical reads. To address these, the team implemented asynchronous processing, decoupled infrastructure, and switched to an OLAP database, ClickHouse, for better query optimization. They also leveraged Redis for caching and S3 for persistent storage, which significantly improved performance and reliability. The recent V3 release, praised by both cloud and self-hosting users, marks a milestone in Langfuse's journey, demonstrating the success of their iterative "hypothesis-experiment-feedback" loop. The team plans to maintain a data-driven culture and expand their operations, inviting interested candidates to join their efforts in Berlin.