Senior II Engineer

Senior II Engineer LocationLondonEmployment TypeFull timeDepartmentEngineeringAbout 9fin9fin 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.We're looking for a Senior Engineer II to take broad technical ownership of the backend systems powering 9fin's platform.You will sit between our Senior and Staff engineering tracks. You will own meaningful systems end to end, lead multi sprint initiatives across a product domain, and shape how we build for scale. You will operate as a strong senior IC, leading design, raising the engineering bar through review and mentorship, and partnering closely with Product, Data, and our financial and legal domain experts.This role suits someone who has already grown beyond a typical senior remit. You enjoy diving into distributed systems problems, and you have firsthand experience scaling services under real production load.What you'll doOwn the design and delivery of significant backend systems and services across a product domain, from data modelling through API surface to operational concerns.Lead complex, multi sprint engineering initiatives that span several engineers and stakeholders.Drive scaling work: identify bottlenecks, propose architectural changes, and execute migrations safely in production.Make pragmatic decisions about distributed systems concerns including consistency, idempotency, partitioning, retries, and observability.Contribute to platform level discussions on service boundaries, data ownership, and how systems evolve as we enter new markets.Run thorough code reviews, mentor senior and mid level engineers, and help define what good looks like in the codebase.Partner with cross functional teammates from Product, Data Engineering, and our editorial and legal domain experts to scope work and ship the right thing.Improve developer experience by investing in tooling, testing, observability, and the paved road so the whole team moves faster.Ramp on legacy areas of the system, find the highest leverage cleanup, and execute it without stalling delivery.Use AI assisted engineering to move faster on understanding, prototyping, and shipping code.Our backend stackPython is the dominant backend language.Flask and FastAPI, with strong typing and Pydantic powering automated documentation and API definitions.PostgreSQL at the heart of most services.AWS for cloud hosted services, with heavy use of AWS Lambda serverless.Docker on AWS ECS for uniform development and deployment.Internal developer platform with a standardised paved road from code to production, plus managed preview environments and feature flags.What we're looking forYou will be a great fit if you have:Several years operating as a senior backend engineer, with a clear track record of leading technical initiatives end to end across a product domain.Experience contributing to the design of distributed systems in production, including the operational realities such as failure modes, observability, data consistency, and graceful degradation.A track record of solving scaling problems, whether database scaling, throughput, latency, or cost. You can talk through a real example end to end: how you measured the problem, what...