Staff Backend Engineer (d/f/m)

At Kleinanzeigen, search is the beating heart of how millions of users discover listings every day. We're evolving our search platform — moving to Vespa, expanding semantic and vector search capabilities, and building ranking models grounded in real buyer and seller signals. We're looking for a Senior Search Engineer who bridges the gap between search infrastructure and data science: someone who can both architect a high-performance retrieval pipeline and run rigorous offline experiments to validate relevance improvements.

You'll join our Core Experience engineering team and work closely with Product, UX, and fellow engineers to shape search quality for one of Europe's largest classifieds platforms.

• Design and implement search features end-to-end: from indexing pipeline changes and schema design to query rewriting, ranking, and autocomplete.
• Lead data-driven technical initiatives — write RFCs grounded in query log and user behaviour analysis, then own delivery from design to production.
• Champion semantic and vector search: design embedding-based retrieval components, integrate LLMs for query understanding or evaluation, and measure real impact via A/B experiments.
• Build and maintain offline evaluation pipelines (relevance judgment, NDCG, MRR) to accelerate the feedback loop between experimentation and deployment.
• Improve indexing reliability and throughput — reduce re-ingestion times, ensure consistency, and tighten SLAs.
• Contribu