Lead Senior Backend Engineer (Python, AI Infrastructure)

About the role

T-Systems Iberia is looking for a senior backend engineer with strong Python skills and system design experience to own the architecture and evolution of the backend platform behind its AI inference endpoints. This is a multi-tenant system handling authentication, API key management, usage metering, billing and request routing, built for high availability and millions of requests. The role is high ownership and involves shaping architecture decisions and raising engineering quality.

Key responsibilities

• Design and build core platform services: API gateway, authentication, authorization, key rotation and multi-tenant isolation.
• Implement and optimize APIs and backend systems with Python frameworks such as FastAPI (or Flask, Django).
• Build usage metering, billing integration and rate limiting for inference endpoints.
• Build and maintain scalable microservices and a high-throughput proxy/routing layer for AI model serving traffic.
• Design telemetry and observability: structured logging, distributed tracing, metrics and alerting.
• Set up CI/CD pipelines, monitoring and observability for production systems.
• Drive architecture, data modeling and technology choices, and improve performance, reliability and latency.
• Establish engineering standards for testing, code review, CI/CD and deployment, and ensure security and compliance.
• Collaborate with the ML infrastructure team on model serving systems (e.g. NVIDIA Dynamo, vLLM, SGlang, TensorRT-LLM).

Required profile

• Degree in Computer Science, Software Engineering or equivalent professional experience.
• 5+ years building and operating backend systems in production at meaningful scale, focused on API design and high-scale environments.
• Proven experience designing and maintaining REST APIs (REST, gRPC, WebSockets, SSE, Webhooks) in production.
• Solid understanding of distributed systems, authentication/authorization (OAuth2, JWT, API keys, RBAC/ABAC) and cloud infrastructure (AWS, GCP, Azure) with Docker and Kubernetes.
• Fluent English, able to collaborate in international teams.

Required skills

• Strong Python and at least one systems-oriented language (Go, Rust, Java, C++); deep knowledge of asynchronous programming and Python profiling.
• Nice to have: DevOps practices, infrastructure as code, GitOps, Prometheus, Grafana, OpenTelemetry, load testing, and exposure to ML serving infrastructure.

What we offer

• Hybrid work model and flexible working hours.
• Customized training via Coursera, weekly language classes and international mentoring sessions.
• Flexible compensation plan covering health insurance, meal vouchers, childcare and transport.
• 26+ working days of vacation, free specialist services and 100% salary coverage during medical leave.