Senior Backend Engineer; LLM​/AI

🧠 Senior Backend Engineer (LLM / AI Experience)

Hybrid
· Tech Team
· Full-time
📍 Barcelona, Spain

• Build and scale backend systems powering conversational AI & digital humans
• Hands-on senior role balancing architecture + production code
• Work deeply with LLMs, RAG pipelines, and real-time systems

• 📍 Barcelona (hybrid) or remote in Europe | 💰 €50k–€65k

Why 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.

At
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.

We’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.

• Actively participate in architectural decisions with the Head of Engineering
• Collaborate with the Cloud Infrastructure Engineer on platform architecture, observability (monitoring, logging, alerting), and deployment strategies
• Design and optimize systems: performance profiling, database queries, caching, and resource usage
• Own production operations: troubleshooting, incident response, and on-call
• Provide technical guidance through code reviews, design discussions, and best practices
• Collaborate on real-time streaming architecture with the Video Synthesis Engineer

• Implement backend features and services in production-grade Python and Go
• Build 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

• Python (FastAPI) and Go (gRPC services)
• AWS (S3, EC2, Lambda, Bedrock, managed services)
• Docker, Kubernetes, Rabbit
  
  MQ, Redis
• LLM APIs (OpenAI, AWS Bedrock)

• 5+ years of backend engineering experience with distributed systems, microservices, and real-time architectures (Web Socket, gRPC, event-driven)
• Experience building and deploying complex, highly-performant Python applications
• 2+ years building LLM-powered products in production (2022–2025), including hands-on experience with LLM APIs (OpenAI, Anthropic, AWS Bedrock) and RAG systems
• Comfortable balancing architecture design with hands-on implementation
• Strong AWS experience with focus on performance optimization, observability, and production operations
• Proven ability to optimize production systems (latency, throughput, technical debt)
• Excellent collaboration skills across backend, infrastructure, and AI/ML teams

• Golang experience
• Experience with video streaming, media processing, or conversational AI platforms
• Data engineering or ML model serving infrastructure experience

First 6 months

• Knowledge transfer completed and ownership of critical backend services established
• Multi-document knowledge base and conversation features live in production
• Active contributor to architecture discussions with measurable performance improvements
• Production systems well-monitored with improved observability

First 12 months

• Core backend services and RAG pipeline running reliably in production
• Platform-wide performance optimizations delivered (Q1–Q3 targets met)
• Backend engineers unblocked and supported through your technical guidance
• Recognized as the go-to…