Backend Engineer - AI/ML

As a Senior Backend Engineer at Proximity, you will be responsible for building and operating core AI/ML-backed systems that power large-scale, consumer-facing products. You are expected to have hands-on experience in shipping ML-backed backend systems in production. **Role Overview:** You will work on production-grade AI runtimes, retrieval systems, and ML-adjacent backend infrastructure, making pragmatic tradeoffs across quality, latency, reliability, and cost. At Proximity, you will not just build APIs but also own critical backend systems end-to-end, collaborate closely with Applied ML and Product teams, and help define the foundations that power intelligent experiences at scale. **Key Responsibilities:** - Own and deliver end-to-end backend systems for AI product runtime, including orchestration, request lifecycle management, state/session handling, and policy enforcement. - Design and implement retrieval and memory primitives, covering end-to-end document ingestion, chunking strategies, embeddings generation, indexing, vector/hybrid search, re-ranking, caching, freshness, and deletion semantics. - Productionize ML workflows and interfaces, including feature and metadata services, online/offline parity, model integration contracts, and evaluation instrumentation. - Drive performance, reliability, and cost optimization, owning P50/P95 latency, throughput, cache hit rates, token and inference costs, and infrastructure efficiency. - Build observability by default, including structured logs, metrics, distributed tracing, guardrail signals, failure taxonomies, and reliable fallback paths. - Collaborate closely with Applied ML teams on model routing, prompt and tool schemas, evaluation datasets, and release safety gates. - Write clean, testable, and maintainable backend code, contributing to design reviews, code reviews, and operational best practices. - Take systems from design to build to deploy to operate, including on-call ownership and incident response. - Continuously identify bottlenecks and failure modes in AI-backed systems and proactively improve system robustness. **Qualifications Required:** - Bachelor's degree in Computer Science, Engineering, or a related field, or equivalent practical experience. - 6-10 years of experience building backend systems in production, with 2-3 years working on ML/AI-backed products such as search, recommendations, ranking, RAG pipelines, or AI assistants. - Strong practical understanding of ML system fundamentals, including embeddings, vector similarity, reranking, retrieval quality, and evaluation metrics (precision/recall, nDCG, MRR). - Proven experience implementing or operating RAG pipelines, covering ingestion, chunking, indexing, query understanding, hybrid retrieval, and rerankers. - Solid distributed systems fundamentals, including API design, idempotency, concurrency, retries, circuit breakers, rate limiting, and multi-tenant reliability. - Experience with common ML/AI platform components, such as feature stores, metadata systems, streaming or batch pipelines, offline evaluation jobs, and A/B measurement hooks. - Strong proficiency in backend programming languages and frameworks (e.g., Go, Java, Python, or similar) and API development. - Ability to work independently, take ownership of complex systems, and collaborate effectively with cross-functional teams. - Strong problem-solving, communication, and system-design skills. **Additional Details:** Proximity is a global team of coders, designers, product managers, geeks, and experts. They solve complex problems and build cutting-edge technology at scale. The team of Proxonauts is growing quickly, providing significant impact on the company's success. Working at Proximity means challenging yourself daily and growing alongside some of the best minds in the industry. As a Senior Backend Engineer at Proximity, you will be responsible for building and operating core AI/ML-backed systems that power large-scale, consumer-facing products. You are expected to have hands-on experience in shipping ML-backed backend systems in production. **Role Overview:** You will work on production-grade AI runtimes, retrieval systems, and ML-adjacent backend infrastructure, making pragmatic tradeoffs across quality, latency, reliability, and cost. At Proximity, you will not just build APIs but also own critical backend systems end-to-end, collaborate closely with Applied ML and Product teams, and help define the foundations that power intelligent experiences at scale. **Key Responsibilities:** - Own and deliver end-to-end backend systems for AI product runtime, including orchestration, request lifecycle management, state/session handling, and policy enforcement. - Design and implement retrieval and memory primitives, covering end-to-end document ingestion, chunking strategies, embeddings generation, indexing, vector/hybrid search, re-ranking, caching, freshness, and deletion semantics. - Productionize ML workflows and interfac