Senior Backend Engineer | Early-Stage AI FinTech | London | Up to £80k + Equity | C#/Python
OB have recently partnered with an early-stage AI fintech start-up that’s building from the ground up, and they’re looking for a Senior Backend Engineer to join the early team and have genuine ownership over the product and platform.
This is a high-agency role for someone who wants to build, ship and own rather than inherit an established codebase.
What you’ll be doing
- Design, build and own core backend services, APIs and infrastructure
- Build event-driven, multi-tenant systems from the ground up
- Ship LLM and agentic workflows into production
- Own data models, failure modes, auditability and system performance
- Build API-first products and infrastructure
- Work directly with the founders and have a major influence on technical direction
- Be comfortable jumping into React / Frontend when a feature needs it
What they’re looking for
- 3–4+ years building, shipping and owning backend systems
- Strong experience with C# and/or Python
- Experience working with AI tooling / LLMs / agentic systems
- Fintech experience is essential, ideally across payments, banking, open finance, ledgers or adjacent financial infrastructure
- Comfortable working across the stack when needed, React experience is a bonus
- Someone who enjoys ambiguity, moves quickly and is comfortable taking ownership
The opportunity
You’ll be joining at a genuinely early stage, meaning you’ll have high agency, direct founder exposure and significant influence over what gets built and how.
You’ll be building core infrastructure for an AI-native fintech from the ground up.
Early team | High ownership | Fast-paced | AI + FinTech
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