? 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 (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

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)

? Versátil 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 [email protected] — creativity is welcome ?

? Recruitment Process

1. Intro call with Joyce (30 min)

2. Technical interview with Head of Engineering & Product Manager (90 min)

3. Team meeting with backend video synthesis, and/or infrastructure engineers (90 min)

4. Practical exercise (short, relevant implementation task)

5. Reference check

⏱️ Timeline: 2–3 weeks from application to offer

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

📌 Senior Backend Engineer (LLM / AI Experience) (Barcelona)
🏢 Importante grupo
📍 Barcelona