Senior AI Engineer - LLMs and Finetuning in London

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.

The Opportunity

The Data Science team is growing at 9fin! We are doing world-class work with groundbreaking technologies to build data-driven products using machine learning, computer vision, natural language processing, speech and audio, and knowledge/data mining. We are looking for a Senior AI Engineer to accelerate our application of AI across teams and products. Come and join us, you will get to build large-scale AI powered systems, learn and apply the latest techniques, and work alongside other great researchers and engineers!

Every day is different, but here's an example of the kind of things you'll work on:

• Design and build generative AI applications tailored to complex financial and legal workflows, leveraging state-of-the-art models to deliver innovative, practical solutions that streamline decision-making and unlock new efficiencies.
• Drive end to end model development lifecycle, leading the team in best practices, ensuring reproducible research and well managed model delivery/deployment.
• Collaborate cross functionally to share diverse ideas, understand business problems, and elevate/mentor your teammates.
• Translate complex problems into well-defined scoped bets in an internal startup style environment, dynamic and fast-paced.
• Learn and apply ground-breaking research and approaches in advanced topics, iterating improvements with a fail fast mentality.
• Be a proactive sharer of compelling ideas/work to the rest of the team and organisation. We want you to help lead/push the adoption of AI throughout 9fin.

What Makes This Role Different

This role is focused on improving the models themselves. While experience with retrieval systems, knowledge graphs, and AI applications is valuable, the core challenge is building proprietary financial-domain models that outperform general-purpose LLMs on the workflows that matter most to 9fin users.

About You

This role will be a great fit if you:

• Open-Weight LLMs: Deep experience evaluating, adapting, and deploying open-weight models such as Llama, Qwen, Mistral, and Gemma for production use cases.
• Fine-Tuning & Post-Training: Expertise in supervised fine-tuning, preference optimisation, instruction tuning, and domain adaptation to improve model performance on specialised tasks.
• Training Data & Synthetic Data Generation: Strong experience building high-quality datasets, generating synthetic training data, and creating data flywheels that continuously improve model quality.
• Model Evaluation: Ability to design rigorous benchmarks, evaluation frameworks, and regression testing systems that measure real-world model performance.
• Financial Domain Modelling: Experience applying AI to complex financial and legal domains, including credit, restructuring, debt instruments, filings, court documents, and capital markets workflows.
• Training Infrastructure: Familiarity with distributed training, parameter-efficient fine-tuning, GPU optimisation, inference acceleration, and cost-performance trade-offs.
• Model Optimisation: Experience with distillation, quantisation, and other techniques for improving model quality, latency, and operating costs.
• Production ML Engineering: Ability to build and operate training pipelines, deployment systems, evaluation infrastructure, and model monitoring in production environments.
• Strong proficiency in Python for production ready delivery.
• You have a strong product focus with a desire to understand the end-to-end impact of your solutions for our end users.
• Good knowledge of AWS’s AI infrastructure.

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.

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

AI experimentation budget of £800 (UK) per employee to trial AI tools

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.