Lead Senior Backend Engineer; m​/f​/d

Puesto: Lead Senior Backend Engineer (m/f/d)
Job  Senior Backend Engineer (m/f/d)
A Coruña, Bilbao, Gijón, Granada, Madrid, Reus, Seville, Valencia Professional Regular T-Systems Iberia 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.

This is a high-ownership role where you will shape architecture decisions, raise the bar of engineering quality and build systems that are performant, secure and observable '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.

Must Have Skills Degree in Computer Science, Software Engineering, or equivalent professional experience5+ years of experience building and operating backend systems in production with meaningful scale5+ years of experience developing backend systems with a focus on API design and high-scale production environments

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, Web Sockets, and SSE protocols and understanding of the tradeoffs between them

Experience with websockets, SSE, and Webhooks Solid understanding of distributed systems including consistency, fault tolerance, concurrency, performance and networking

Solid understanding of data pipelines and performance optimization

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

Experience…