Senior Backend Engineer (LLM / AI Experience)Hybrid Tech Team Full-time Barcelona, SpainIn a few wordsBuild and scale backend systems powering conversational AI & digital humansHands-on senior role balancing architecture + production codeWork deeply with LLMs, RAG pipelines, and real-time systems Barcelona (hybrid) or remote in Europe | 50k-65kWhy this role is exciting: You'll shape the backend foundations of a cutting-edge digital human platform, where your architectural and performance decisions directly impact real-time AI experiences used by enterprise customers.About UNITHAt UNITH, we're transforming customer journeys with conversational AI. Listed on the ASX, we create lifelike digital humans using cutting-edge synthetic facial movement, voice engineering, and conversational design.Our digital humans speak 60+ languages with 600+ voices, redefining how businesses interact with customers worldwide. The RoleWe're looking for a Senior Backend Engineer with recent LLM product experience who combines strong architectural thinking with hands-on development.You'll work closely with the Head of Engineering, playing a key role in technical decisions while remaining deeply involved in day-to-day coding, feature delivery, and system optimization. You'll be a senior technical voice on the team someone who designs systems and builds them. What You'll DoArchitecture & System Operations (50%)Actively participate in architectural decisions with the Head of EngineeringCollaborate with the Cloud Infrastructure Engineer on platform architecture, observability (monitoring, logging, alerting), and deployment strategiesDesign and optimize systems: performance profiling, database queries, caching, and resource usageOwn production operations: troubleshooting, incident response, and on-callProvide technical guidance through code reviews, design discussions, and best practicesCollaborate on real-time streaming architecture with the Video Synthesis EngineerFeature Development & Implementation (50%)Implement backend features and services in production-grade Python and GoBuild conversation features: state management, history, and intelligence improvements Implement multi-document knowledge bases using AWS Bedrock Integrate LLM APIs (OpenAI, AWS Bedrock) and build RAG pipelines Develop APIs and service integrations (gRPC, REST) Work on core backend services: orchestration, caching, and platform APIs Own testing, CI/CD pipelines, and deployment automation Tech StackPython (FastAPI) and Go (gRPC services)AWS (S3, EC2, Lambda, Bedrock, managed services)Docker, Kubernetes, RabbitMQ, RedisLLM APIs (OpenAI, AWS Bedrock) What We're Looking ForMust-Have5+ years of backend engineering experience with distributed systems, microservices, and real-time architectures (WebSocket, gRPC, event-driven)Experience building and deploying complex, highly-performant Python applications2+ years building LLM-powered products in production (2022-2025), including hands-on experience with LLM APIs (OpenAI, Anthropic, AWS Bedrock) and RAG systemsComfortable balancing architecture design with hands-on implementationStrong AWS experience with focus on performance optimization, observability, and production operationsProven ability to optimize production systems (latency, throughput, technical debt)Excellent collaboration skills across backend, infrastructure, and AI/ML teamsBonus PointsGolang experienceExperience with video streaming, media processing, or conversational AI platformsData engineering or ML model serving infrastructure experience What Success Looks LikeFirst 6 monthsKnowledge transfer completed and ownership of critical backend services establishedMulti-document knowledge base and conversation features live in productionActive contributor to architecture discussions with measurable performance improvementsProduction systems well-monitored with improved observabilityFirst 12 monthsCore backend services and RAG pipeline running reliably in productionPlatform-wide performance optimizations delivered (Q1-Q3 targets met)Backend engineers unblocked and supported through your technical guidanceRecognized as the go-to expert for backend + LLM implementation What We OfferCompensation & Flexibility Salary: 50,000 - 65,000, depending on experience Hybrid work in Barcelona or remote options within EuropeImpact & GrowthOwnership of critical backend services used daily by enterprise customersHands-on technical work alongside architectural responsibilityDeep technical challenges across LLMs, RAG pipelines, real-time systems, and scalabilityHigh-impact role in a small, senior team (12 people)Close collaboration with Engineering, AI research, and infrastructure teamsOpportunity to build expertise in the fast-evolving digital humans domainAdditional Perks Office in the center of Barcelona Work from anywhere Lunch compensation when in the office Private health insurance with Alan Travel allowance (for team members living 10km+ from the office) Flexible benefits (tax-free under Spanish legislation) ClassPass discount How to Apply:Submit: Your CV highlighting ML production experience A short motivation (3-5 sentences) covering:Backend systems you've built and maintainedLLM features you've implemented in productionA performance optimization project you worked onYour experience with RAG or knowledge basesWhy digital humans excite youApply via the Easy Apply button, or reach out directly to [email protected] creativity is welcome Recruitment Process Technical interview with the tech team (60 min) Small take-home assignment Assignment review (60 min) Reference check Call with Joyce (30 min) Timeline: 2-3 weeks from application to offerReady to make digital humans faster, better, and more reliable?