Principal Software Engineer

Senior Backend Engineer | London | £100,000 - £160,000 | Python | FastAPI | Systems

Location: London based - hybrid

Salary: £100,000 - £160,000 + equity

Tech Stack:

• Backend: Python (FastAPI)
• Cursor, Claude Code
• AWS

Are you a backend engineer who cares more about building robust systems than chasing AI hype?

We are working with a recently funded Series A technology company building AI powered automation for real world, critical workflows. Their platform captures operational knowledge and turns it into production grade systems that AI can interact with safely and reliably.

This is not applied machine learning, not foundation model development, and not experimental agent playgrounds.

The work is focused on the engineering around AI: evaluation, control, reliability, and building systems that behave predictably in production. Engineers work closely with users, own problems end to end, and shape both the technical and product direction in a small, high trust team. It is an intellectually demanding environment where quality, correctness, and long term system design genuinely matter.

Responsibilities

• Design and build backend systems that power a complex, evolving platform using Python
• Own data models, schemas and database design with a strong focus on correctness and scale
• Build ingestion pipelines and integrations with production customer systems
• Develop tooling that enables AI capabilities while maintaining strong control and evaluation standards
• Work directly with customers to understand workflows and translate them into reliable systems
• Contribute to architectural decisions and long term platform evolution

Requirements for Success

• Strong experience as a backend or systems focused engineer
• Deep Python experience with excellent engineering fundamentals, or equivalent depth in a strongly typed language
• Strong SQL skills and experience designing schemas
• Experience building complex backend systems that evolve over time
• Comfort working in ambiguous, early stage product environments
• Experience with data ingestion pipelines or internal tooling for AI or data teams

The engineering team is currently small and senior, with a strong academic and systems background. There is no formal product team. Engineers own user experience, technical decisions and delivery. The culture values thinking time, technical rigour and clear communication over speed for its own sake.

Benefits

• Salary between £120,000 and £160,000 depending on experience
• Meaningful equity
• High ownership role with direct influence on product and technical direction

This role will not suit engineers who want to build flashy demos or constantly switch problems. It will suit someone who enjoys hard systems, deep thinking, and building things that actually hold up in the real world.

If you're looking for a role where you can make meaningful decisions, work on incredibly interesting and complex problems, and be part of an exceptional team, get in touch at imogen@sr2rec.co.uk.