Senior Back End Engineer

Elixirr Digital is transforming how consulting services are delivered. This role is critical to designing and implementing the backend infrastructure that powers our AI-driven solutions and internal agent platform.

As a Senior Back End Engineer, you will design and build scalable, production-grade backend services primarily using Python and FastAPI, while integrating AI capabilities into the systems and products we develop.

We’re looking for someone who combines strong backend engineering fundamentals with hands-on experience working with AI in production. You’ll be expected to independently design solutions, make technical decisions, and take ownership from idea through implementation.

This is an engineering role for someone who wants to move fast in a modern, AI-assisted software development lifecycle and actively uses AI development tools to improve the way software is built.

At Elixirr Digital, you’ll have the opportunity to work with advanced technologies, grow alongside a team of talented professionals, and make a lasting impact across diverse industries.

Candidates applying for employment contract kindly note this position is a hybrid working opportunity from our locations in Rijeka or Zagreb.

What you will be doing as a Senior Back End Engineer at Elixirr Digital?

Backend Architecture & Development

• Design, build, and maintain scalable backend services using Python and FastAPI.

• Take end-to-end ownership of backend components and features, from solution design and technical decision-making through implementation, testing, and deployment.

• Build production-grade services with scalability, performance, reliability, and maintainability in mind.

• Design and integrate APIs, internal systems, and third-party services.

• Work within our AWS and Azure ecosystem to develop and operate backend solutions.

• Identify technical trade-offs, propose solutions, and communicate architectural decisions clearly to the wider team.

AI-Enabled Backend Engineering

• Build and integrate AI and LLM capabilities into production backend systems.

• Work with AI and agent frameworks to integrate models, agents, and AI-powered services into our platform.

• Design backend services that support scalable AI inference, streaming, and increasing system throughput.

• Build integrations between AI tooling, internal data and services, and third-party systems.

• Contribute to building scalable, reliable, and production-ready AI-enabled systems.

• Work closely with AI Engineers to bridge strong backend engineering practices with our growing AI ecosystem.

Security & Production Readiness

• Build backend services with security, reliability, and production readiness in mind from the start.

• Apply authentication and authorization practices when designing and implementing APIs and backend services.

• Follow secure coding practices and ensure appropriate protection of sensitive data across services and integrations.

• Design systems with appropriate logging, monitoring, error handling, and observability to support reliable production operations.

• Identify potential security risks and contribute to maintaining secure and resilient backend systems.

AI-Assisted Software Development

• Use modern AI-assisted and agentic development tools such as Codex, Cursor, or similar tools as part of your day-to-day engineering workflow.

• Use AI tooling to accelerate development while maintaining high standards for code quality, security, and maintainability.

• Review and validate AI-generated code with the same rigor as traditionally written code.

• Help continuously improve how AI-assisted development is used across the engineering lifecycle.
  

Cross-Functional Collaboration & Ownership

• Work closely with AI Engineers, DevOps, Front End Engineers, Data teams, and other stakeholders to turn complex requirements into production-ready solutions.

• Contribute to technical discussions and help drive engineering best practices across the team.

• Take ownership of features and components rather than relying on predefined technical solutions.

• Collaborate effectively across our international teams.

Competencies and skillset we expect you to have to successfully perform your job

Technical Expertise

• Strong hands-on experience with Python backend development and FastAPI.

• Experience designing, building, and operating production-grade backend systems.

• Experience working with AWS and Azure cloud-native environments.

• Hands-on experience integrating AI/LLM capabilities into production applications, beyond experimentation or simply consuming AI tools.

• Experience working with AI or agent frameworks such as LangChain, LangGraph, Google ADK, or similar technologies.

• Experience designing APIs and integrating internal and third-party services.

• Strong understanding of scalable backend architectures and experience building systems designed for increasing throughput.

• Strong understanding of backend security principles, including authentication, authorization, API security, and secure handling of data.

• Experience with relational and/or NoSQL databases.

• Demonstrable experience using AI-assisted and agentic development tools, such as Codex, Cursor, or similar tools.

Preferred Qualifications

• Experience creating, managing, or integrating MCP servers.

• Experience with AI observability tools, such as LangFuse or similar technologies.

• Experience with observability in high-scale or AI-enabled production systems.

• Familiarity with containerization and modern CI/CD practices.

• Previous experience working in consulting or professional services environments.

• Experience working in distributed international teams.