Lead Senior Backend Engineer (m/f/d)

Job Description T-Systems is at the forefront of innovation, delivering advanced technology solutions across sectors including automotive, healthcare, and public services. Our AI Foundation Services team builds the platform infrastructure that powers AI inference at scale, including API gateways, authentication, billing, and multi-tenant serving. designs and builds high-performance backend systems and APIs that power intelligent applications across diverse industries. We cultivate a collaborative engineering culture where technical depth creativity and ownership technical expertise drive real-world impact.

Role Overview We are looking for a senior backend engineer highly skilled Python Developer with strong system design skills and experience building production infrastructure deep experience designing, building, and scaling distributed systems and APIs. In this role, Y y You will ou will own architect and drive the evolution of the maintain backend platform behind our AI inference endpoints - a multi-tenant system handling authentication, API key management, usage metering, billing and request proxy services that enable high-availability, data-intensive AI-powered solutions. The role is high-ownership and you will shape architecture decisions, raise the bar of engineering quality and build systems that are performant, secure and observable at scale. You’ll collaborate with experts in AI infrastructure and data engineering to build robust, secure, and efficient systems that scale to millions of requests.

Your Task

We are looking for a senior backend engineer with strong system design skills and experience building production infrastructure. This role involves architecting and maintaining backend platform services behind AI inference endpoints - a multi-tenant system handling authentication, API key management, usage metering, billing and request proxy. You will own and drive the evolution of backend services that enable high-availability, data-intensive AI-powered solutions. The role is high-ownership and you will shape architecture decisions, raise the bar of engineering quality and build systems that are performant, secure and observable at scale. You'll collaborate with experts in AI infrastructure and data engineering to build robust, secure, and efficient systems that scale to millions of requests.

Responsibilities

• Design and build core platform services: API gateway, authentication, authorization, key rotation, and multi-tenant isolation

• Design, implement, and optimize APIs and backend systems using Python frameworks such as primarily FastAPI (or Flask, or Django)

• Architect and implement usage metering, billing integration, and rate limiting for inference endpoints

• Build and maintain scalable, fault-tolerant microservices for data processing and AI integration

• Build and operate a high-throughput proxy/routing layer for AI model serving traffic

• Collaborate with cross-functional teams to design system architecture and ensure seamless system interoperability

• Design telemetry and observability into the platform from the ground up — structured logging, distributed tracing, metrics, and alerting

• Implement robust CI/CD pipelines, monitoring, and observability for high-performance production systems

• Drive technical decisions on architecture, data modeling, and technology choices

• Identify performance bottlenecks and drive improvements in reliability, scalability, and latency

• Establish engineering standards for the backend codebase: testing, code review, CI/CD, and deployment practices

• Ensure best practices for security, compliance, and maintainability across the API lifecycle

• Collaborate closely with the ML infrastructure team to integrate with model serving systems (e.g., NVIDIA Dynamo, vLLM, SGlang, TensorRT-LLM)

Your Profile

We are seeking a Senior Backend Engineer / Python Developer with extensive experience in building and operating production backend systems at scale, strong system design skills, and deep expertise in distributed systems and API development. The ideal candidate will have proven experience with authentication systems, cloud infrastructure, and modern Python development practices.

Must Have Skills

• Degree in Computer Science, Software Engineering, or equivalent professional experience

• 5+ years of experience building and operating backend systems in production with meaningful scale

• Strong proficiency in Python with deep knowledge of asynchronous programming, modern Python tooling and profiling

• Proficiency in at least one systems-oriented language (Go, Rust, Java, C++)

• Willingness to work across the current stack which includes Python (FastAPI)

• Proven experience designing and maintaining REST APIs in production environments

• Experience with REST, gRPC, WebSockets, and SSE protocols and understanding of the tradeoffs between them

• Experience with webhooks in production environments

• Solid understanding of distributed systems including consistency, fault tolerance, concurrency, performance and networking

• Experience with data pipelines and performance optimization

• Experience designing authentication and authorization systems (OAuth2, JWT, API key management, RBAC/ABAC)

• Experience with cloud infrastructure (AWS, GCP, or Azure)

• Experience with containerized environments (Docker)

• Experience with container orchestration (Kubernetes)

• Understanding of database design (SQL, ORMs) and data modeling at scale

• Fluent in English (written and verbal)

• Comfortable collaborating in international teams

Nice to Have Skills

• Experience with high-throughput, low-latency or real-time systems (e.g., message queues, event-driven architectures)

• Familiarity with generative AI or large language models (e.g., integration of AI APIs, RAG workflows, or vector databases)

• Knowledge of modern DevOps practices

• Experience with infrastructure as code

• Knowledge of GitOps workflows

• Experience with observability tools (Prometheus, Grafana, OpenTelemetry)

• Exposure to ML serving infrastructure (model servers, GPU scheduling, inference optimization)

• Comfortable occasionally touching or contributing to frontend code when necessary

• Experience in stress/load-testing and evaluating performance of production systems

• Strong problem-solving mindset and commitment to code quality and performance excellence

• Track record of improving engineering culture: mentoring junior engineers, introducing better practices, leading technical discussions

Additional Information What do we offer you?

• Work environment & flexibility

• International, dynamic and collaborative environment

• T-Social: social initiatives (sports, community, health, ...)

• Hybrid work model (remote/on-site)

• Flexible working hours

• Growth & development

• Customized training: access to Coursera to learn whatever you want, whenever you want

• Weekly language classes (English, Spanish & German)

• International Mentoring Sessions & Experience Days

• Compensation & benefits

• Flexible compensation plan (health insurance, meal vouchers, childcare, transport)

• Telemedicine

• Life and accident insurance

• Social fund

• Wellbeing & time off

• 26+ working days of vacation per year

• Free access to specialist services (medical, legal, wellness)

• 100% salary coverage during medical leave

• And many more advantages of being part of T-Systems!

If you are looking for a new challenge, do not hesitate to send us your CV! Please send CV in English. Join our team! T-Systems Iberia will only process the CVs of candidates who meet the requirements specified for each offer.