Senior Backend Engineer

About 9fin

9fin is the AI platform powering global debt markets — the world’s largest asset class at over $145 trillion.

Debt markets are vast, global, and mission-critical, yet still run on fragmented data, PDFs, and manual workflows. 9fin replaces this broken infrastructure with a single platform that centralises proprietary credit data, deep analysis, and high-value workflows across global markets.

Today, 9fin powers teams at 300+ blue-chip institutions worldwide, including global banks, asset managers, private equity firms, law firms, and advisors. The business is scaling at exceptional speed, with rapid expansion in the US and best-in-class retention driven by deep workflow adoption.

We’re at a defining inflection point. With proven product-market fit and strong, global market pull, 9fin is accelerating toward becoming the category-defining platform for debt markets worldwide.

What you'll work on

Join 9fin's cross-functional Search and AI team, where you'll play an impactful role in shaping how our users find and interact with the information and content on the 9fin platform. The current team has expertise across backend, frontend, design, data science and product.

As a backend engineer on the team, you will:

• Drive the development of backend services and APIs that power our AI tools, including generative AI features.

• Build and optimise the backend systems that underpin 9fin’s search experience, focusing on performance, scalability and reliability. You’ll work with technologies like Elasticsearch for complex data retrieval.

• As a senior IC, you’ll raise the bar for our engineering practices. This includes leading code reviews, mentoring other engineers, contributing to technical architecture and providing input on new features and products.

• Get involved in early research, experimentation and proof-of-concepts with new technologies, especially as we enhance our AI and search offerings for our users.

• Work across a broad and complex backend, tackling changes in financial data modelling, access control logic, integrating ML/AI prediction services, and building data visualisation infrastructure.

• Drive codebase health through impactful refactoring, automation and clear documentation.

• Take ownership of projects and features, driving them from initial scoping through to delivery, taking part in the full software development lifecycle.

• Work directly with product managers, designers, data scientists and our financial, legal and editorial teams. Your ability to explain and break down complex projects to non technical audiences will enable productive and efficient team progress.

Our Backend Stack

Our core backend is built primarily with Python, leveraging:

• Elasticsearch for search capabilities

• Flask & FastAPI

• Typing is used within our Python stack to power automated documentation and API definitions

• Relational Databases (PostgreSQL) at the heart of majority of services

• We have our own internal developer platform with standardised paved road approaches to infrastructure to bring your code into production as quickly as possible.

• We’re AWS for Cloud hosted services

• Heavy use of AWS lambda Serverless

• Docker (AWS ECS) for uniform development/deployment from dev to prod

Requirements

This role will be a great fit if you have:

• Experience operating as a Senior IC Engineer, leading systems design and infrastructure discussions, mentoring more junior team members, and scoping work within cross-functional product teams.

• Backend expertise:

  • Experience with Python and its web frameworks (we currently use FastAPI with strong typing & Pydantic)

  • Experience designing data flow through software, from persistent storage to API endpoints, while applying industry best practices for validation

  • Good working knowledge of SQL statements for retrieving data

• Search and AI:

  • Experience with or a strong understanding of search technologies (eg. Elasticsearch, OpenSearch, Solr) or experience with high-performance NoSQL databases for information retrieval.

  • A strong interest in Generative AI and broader AI concepts

• Collaboration and quality:

  • The ability to plan and reason about software effectively, clearly and compellingly communicating its purpose within systems and its business impact on clients

  • Strong communication skills, and are comfortable collaborating with colleagues across various roles and specialisms.

  • Code Quality: Through writing testable, maintainable code, and by engaging in code review for your own work and for reviewing others

Benefits

We’re a scaling start up and we enjoy sharing our success, when the company succeeds, we always reinvest that in our people. We also offer huge amounts of responsibility, an abundance of opportunity for growth and a platform to truly excel.

Financial & Insurance

• Competitive Salary (our salary bands are benchmarked at the top end of the market)

• Pension (your minimum contributions are 4% with 9fin matching up to 7%)

• Private Medical Insurance

• Paid sick leave with Income Protection for long periods of illness

• Group Life Assurance

• Season Ticket Loan & Cycle to Work schemes

Time off

• 25 holiday days per year

• Local public holidays (with the ability to exchange them for alternative days)

• Hybrid working model, to allow you the flexibility to decide how, where and when you do your best work

• Work abroad for up to 3 months a year

• 1 month paid sabbatical after 5 years of service

• Enhanced parental leave & flexible working arrangements available

Training & Culture

• Professional learning and development budget

• Quarterly team socials

• Summer and Winter company social events

9fin is an equal opportunities employer

At 9fin we are dedicated to building and promoting a fair and inclusive workplace where everyone can reach their full potential and truly belong. We recognize that building diverse teams enables a more creative and productive environment. If you’re excited about this role but your experience doesn’t perfectly align with the job description, we encourage you to apply anyway. You might just be who we’re looking for — either for this role, or perhaps another.