Senior Backend Engineer in London

The AI Operating System for Private Capital.

Capsa AI

Private capital funds have to find potential investments, research and analyse them thoroughly, monitor them over time, drive improvements, and decide when to buy and sell.

They've got to see through the marketing.

They've got to outbid the competition.

And they've got to learn from every deal they do.

Historically, these processes have run on people, we are building the AI Operating System that will run them in the future.

We're focused, ambitious, and obsessed with building a category-defining company.

In the last 12 months we've grown ARR 15x, achieved product–market fit with leading multi-billion-dollar PE firms, and expanded across the US, UK, and Europe.

Now we're doubling down: we've raised a large Series A from top-tier VC investors to scale the team.

We're hiring hyper-talented people who want to work at the forefront of AI and revolutionise an industry.

• At a glance
• Role: Senior Fullstack Engineer
• Location: London, UK (Hybrid, in-person 4 days per week)
• Team: Engineering
• Compensation: Top of market. Competitive base + OTE

The role

Take what you already know about building reliable systems, or about infrastructure that has to work at scale, into a category-defining company.

A fast track to owning the backend that powers decisions at the world's leading PE firms.

You'll build and own the services, pipelines, and infrastructure that sit underneath our AI platform - the systems that ingest documents, process financial data, and make everything downstream possible.

Whether you've built high-throughput data pipelines, designed distributed systems that don't fall over, or shipped backend services used by demanding professional users, you bring rigour most engineers don't have, and the job is to point that rigour at problems the industry has never had good tooling for.

This isn't a place to keep the lights on.

We hire engineers who want to build the foundation, not inherit it.

Scope grows fast, ownership is real from day one, and the founding team is close enough that the decisions you make now will shape the architecture for years.

The opportunity

• Build the infrastructure the platform runs on. Design and ship the services, APIs, and systems that underpin everything our AI does, reliable, performant, built to scale.
• Own the data pipelines. Ingest, process, and index large volumes of documents and financial data. The quality of the agent's outputs starts here.
• Expand what the agent can see. Integrate new data sources into the loop and increase the depth and breadth of analysis our customers can perform.
• Support the AI layer. Work closely with the AI team to design and implement backend capabilities that give our agent genuine investment expertise.
• Keep the codebase clean. Uphold rigorous standards across everything you ship. Tech debt is a tax on velocity, and you don't let it accumulate.
• Recent projects include
• Agentic assistant with a finance-focused toolkit and advanced document authoring features
• Scalable document ingestion and indexing pipeline
• In-house, streaming-first agent framework
• AI-assisted document editor
• Track record
• Backend depth, not just breadth.

Four or more years building production software at a venture-backed startup or top tech firm, owning services and systems end-to-end, not just contributing to them.

• You've shipped things that mattered.

Entire features or products taken from ideation to production, with impact you can speak to.

If you can't point to what changed because of your work, that's a flag.

• The right technical toolkit.

Strong Python, hands-on experience with Fast API, Postgres, Elastic Search, Rabbit MQ, Redis, message queues, and distributed systems, or close enough that the gaps close fast.

• Domain curiosity, not just technical ability.

You go deep on the problem, not just the implementation.

You care about what the system does for the person depending on it, and that shows in how you build.

• Comfortable at pace. Fast-moving environments are where you do your best work, not something you tolerate.
• How you operate
• Low ego, high ownership. You want to be part of building something that matters more than you want a title that says so.
• Hungry and resilient. Start-up pace is the appeal, not the trade-off. Rejection doesn't slow you down.
• Bias for action over planning theatre. You move with incomplete information and adjust as you go.
• Genuinely curious about AI. Using it, breaking it, building it into how you work.
• If this opportunity excites you

We'd like to meet you. Initial conversations are direct and substantive, going deep on the work, the team, and what you'd own in the first six months.

Capsa AI provides equal employment opportunities (EEO) to all employees and applicants for employment without regard to race, color, religion, sex, national origin, age, disability, genetics, sexual orientation, gender identity, or gender expression.

We are committed to a diverse and inclusive workforce and welcome people from all backgrounds, experiences, perspectives, and abilities.

Capsa AI is committed to a fair and transparent hiring process.

We confirm that this advertisement is for an active, existing vacancy within our organization.

Please be advised that we may use artificial intelligence-driven tools to assist our recruitment team in screening, assessing, and selecting candidates for this position.

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