Senior Backend Engineer

Senior Backend Engineer (LLM / AI Experience)
Hybrid

• Tech Team
• Full-time Barcelona, Spain In a few words
• 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.

About UNITH
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.

The Role
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.

What You'll Do
Architecture & System Operations (50%)

• 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

Feature Development & Implementation (50%)

• 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

Tech Stack

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

What We're Looking For
Must-Have

• 5+ 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 applications
• 2+ years building LLM-powered products in production , 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

Bonus Points

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

What Success Looks Like
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 expert for backend + LLM implementation

What We Offer
Compensation & Flexibility

• Salary: €50,000 - €65,000, depending on experience
• Hybrid work in Barcelona or remote options within Europe

Impact & Growth

• Ownership of critical backend services used daily by enterprise customers
• Hands-on technical work alongside architectural responsibility
• Deep technical challenges across LLMs, RAG pipelines, real-time systems, and scalability
• High-impact role in a small, senior team (12 people)
• Close collaboration with Engineering, AI research, and infrastructure teams
• Opportunity to build expertise in the fast-evolving digital humans domain

Additional 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 maintained
• LLM features you've implemented in production
• A performance optimization project you worked on
• Your experience with RAG or knowledge bases
• Why digital humans excite you

Apply via the
Easy Apply
button, or reach out directly to

— creativity is welcome

Recruitment Process

• Intro call with Joyce (30 min)
• Technical interview with Head of Engineering & Product Manager (90 min)
• Team meeting with backend video synthesis, and/or infrastructure engineers (90 min)
• Practical exercise (short, relevant implementation task)
• Reference check

Timeline:
2-3 weeks from application to offer

Ready to make digital humans faster, better, and more reliable?
Apply now