Founding Senior Product Engineer

Partnering with a well-backed seed-stage AI company in London, Foundation Partners are hiring for several founding Senior Engineers to a technically strong & lean Eng team, shape 'how' in addition to 'what' is built and help the company prepare for the next iteration of their scaling journey.

The Role

This is a full-stack product role with a backend-heavy centre of gravity. You'll own complete product slices end-to-end and you'll ship these without needing to be guided.

You're not a specialist who hands off at the API boundary. You think in user outcomes and delivery units, and you're reliable: your code handles edge cases, your APIs have clean contracts, and the work you ship stays shipped.

What You'll Do

• Own product delivery — take features from spec to production, backend-first but covering frontend and integration where needed

• Build and maintain backend systems — product APIs, data pipelines, and core infrastructure on our Python/FastAPI/Postgres stack

• Build with LLMs and agents — ship product features with significant LLM integration; contribute to the voice agent backend and information extraction systems

• Work across the stack — ship workable React/TypeScript frontend for product features; not a frontend specialist, but comfortable and pragmatic

• Collaborate with product and design — translate ambiguous requirements into concrete shipped work; be the engineer who unblocks, not the one who waits

• Maintain quality at speed — handle data integrity, error paths, API evolution, and operational concerns as a default, not an afterthought

What We're Looking For

• Independent delivery - You can own and ship end-to-end product slices with minimal supervision; your track record shows features that shipped, stuck, and scaled

• Product trade-off judgment — you balance speed, quality, and user impact under ambiguity; you push back when something is underspecified and make pragmatic calls when it needs to ship

• Reliability and API discipline — you handle data integrity, error paths, idempotence, and API versioning as standard practice; production reliability is your default, not a later concern

• Cross-functional pragmatism — you work effectively with product and design, can unblock yourself across the stack, and ship workable frontend when that's what's needed

Strong technical depth in:

• Python backend (FastAPI or equivalent, async patterns, Postgres, Redis)

• LLM integration — building products where AI is in the critical path, not bolted on

• API design and data modelling

• JavaScript/TypeScript — comfortable enough to ship frontend features and review frontend PRs

Nice to Have

• Experience with voice agents or real-time audio pipelines

• Familiarity with evals, guardrails, or agent observability

• Familiarity with GCP / cloud infrastructure

• Experience in recruiting tech, marketplaces, or matching systems

The Stack

A modern Python stack: FastAPI, Postgres, Redis, Docker, Pydantic AI, running on GCP. Frontend in React/TypeScript. We iterate fast and keep the codebase clean.

We'll offer you

• Above market salary

• Meaningful equity

• Full private healthcare & dental

• Fertility benefits & enhanced parental support

• Gym membership & wellness benefits

• LOTS of Claude tokens

• Regular socials, offsites and an annual trip

• MacBook Pro + team kit

• "Whatever you need" approach to tools and support