Senior Backend Developer - Python

iO Associates; England; Hybrid; GBP 60,000 - 90,000; Full time

Job summary

A UK-based deep tech start-up is seeking a Senior Backend Engineer (Python & Django or Flask) to develop scalable backend systems for generative AI products. This hybrid role entails architecting APIs, optimizing databases, and collaborating with AI teams. Ideal candidates have over 5 years of experience in backend development and a strong focus on performance and security.

Qualifications

• 5+ years' backend development with Python (Django or Flask).
• Proven experience designing, scaling, and operating production REST APIs.
• Deep expertise in relational database design and performance tuning.

Responsibilities

• Architect and evolve scalable backend services in Python.
• Design and operate RESTful APIs aligned with OpenAPI.
• Implement authentication and authorization strategies.

Skills

Backend development

Python

Django or Flask

REST API design

PostgreSQL

Docker

AWS services

Problem-solving

Tools

Docker

PostgreSQL

AWS

GitHub Actions

Terraform

Job description

Overview

Senior Backend Engineer - Python

Outside IR35
Hybrid - Oxford or London | Contract

Our client, a UK-based deep tech start-up, is seeking an experienced Senior Backend Engineer (Python & Django or Flask) to own and operate mission-critical backend services powering generative AI products. You'll architect, build, and run scalable APIs and data services end-to-end, collaborating closely with AI engineers to deliver new features from concept to production. This role offers the opportunity to shape the backend systems at the core of cutting-edge AI, with a strong focus on performance, reliability, and security.

Key Responsibilities

• Architect and evolve scalable backend services in Python (FastAPI/Django/Flask).
• Design and operate RESTful APIs aligned with OpenAPI/Swagger.
• Implement authentication and authorization (OAuth2/OIDC, permissions, session management).
• Optimise relational database design and performance (PostgreSQL).
• Introduce caching, rate limiting, and queuing to meet performance goals.
• Integrate with AI pipelines and model-serving endpoints (async inference, streaming).
• Containerise services with Docker; maintain IaC with Terraform/CloudFormation.
• Operate services on AWS with CI/CD pipelines (GitHub Actions/Argo CD).
• Lead security hardening, monitoring, and compliance readiness.
• Own backup, disaster recovery, incident response, and runbook creation.
• Mentor engineers and communicate technical trade-offs to stakeholders.

Requirements

• 5+ years' backend development with Python (Django or Flask).
• Proven experience designing, scaling, and operating production REST APIs.
• Deep expertise in relational database design, performance tuning, and migrations (PostgreSQL).
• Strong knowledge of Docker, Git workflows, and AWS core services (EC2, VPC, IAM, S3, ALB/ELB, ECR/ECS).
• Familiarity with API versioning, testing strategies, and documentation best practices.
• Eligible for SC clearance (or ability to obtain; DV clearance required later).
• Excellent problem-solving, communication, and high ownership.

Desired Skills

• Experience with OpenSearch/ELK, Prometheus, or Grafana for logging/monitoring.
• Knowledge of compliance frameworks (ISO 27001, GDPR, NIST SSDF, OWASP ASVS/SAMM).
• Background in building and operating high-throughput, low-latency services.
• Strong mentoring and technical leadership abilities.

This role is ideal for a high-agency engineer who thrives on building and operating scalable backend systems in production, with the autonomy to directly shape the core infrastructure of a fast-moving AI start-up.