TL;DR
Crimson, a YC X25 startup building an AI assistant for litigation, is recruiting a founding full-stack engineer to join its London office. The role includes end-to-end product ownership, work across a Python backend and Next.js/TypeScript frontend, and a salary of £80–120k plus equity.
What happened
Crimson, a Y Combinator-backed startup focused on applying AI to high-stakes litigation, has posted a founding full-stack engineer role based in London. The company, founded in 2025 and operating with a four-person team led by three co-founders, says its platform helps law firms draft pleadings, summarize transcripts, analyze judgments and surface evidence. The hire will be expected to ship production code immediately and own major features from user research through delivery. The stack includes a Python backend, Next.js with TypeScript frontend, PostgreSQL, state-of-the-art large language models and deployment to Azure using infrastructure-as-code (Bicep) with GitHub Actions for CI/CD. Responsibilities span building document ingestion pipelines, designing AI-native interfaces for litigation workflows, developing multi-step agent processes, and improving system performance and observability. The role requires three-plus years of experience and is primarily onsite (minimum three days per week) near Bank in London.
Why it matters
- Early engineering hires shape product direction and security practices for tools handling sensitive legal files.
- Adoption of AI in litigation could change how complex disputes are prepared and researched for large law firms.
- YC backing and existing relationships with major UK and US firms signal institutional interest in AI legal workflows.
- Hiring in London anchors the startup in a major legal and financial hub, which may aid customer engagement.
Key facts
- Role: Founding Engineer (Full Stack); full-time based in London.
- Salary range: £80,000–£120,000, with meaningful equity (listed 0.50%–1.00%).
- Experience: 3+ years; US citizenship/visa is not required.
- Tech stack: Python backend, Next.js with TypeScript frontend, PostgreSQL, SOTA LLMs.
- Deployment and ops: Azure via IaC (Bicep) and CI/CD with GitHub Actions.
- Responsibilities include document ingestion pipelines, AI-native UX, multi-step agent workflows and system observability.
- Company: Crimson, founded 2025; YC batch X25; team size listed as 4.
- Office policy: minimum three days per week in office near Bank, London.
- Recruiting contact: email founders at founders [at] crimson [dot] law and include a LinkedIn link; the listing states applicants will receive a reply within 24 hours.
What to watch next
- Whether Crimson expands its London engineering team beyond the founding hire (not confirmed in the source).
- Product roadmap and timing for broader customer rollouts or public launches (not confirmed in the source).
- Specific technical and security approaches the startup will adopt as it scales to handle more sensitive case files (not confirmed in the source).
Quick glossary
- Full-stack engineer: A developer who works on both backend and frontend software, often handling databases, APIs, and user interfaces.
- LLMs (Large Language Models): Machine learning models trained on large text corpora that can generate and understand human-like text; used as components in many AI applications.
- IaC (Infrastructure as Code): The practice of provisioning and managing infrastructure through machine-readable configuration files rather than manual processes.
- CI/CD (Continuous Integration/Continuous Delivery): A set of practices and tooling to automate code integration, testing, and deployment to speed up and stabilize software releases.
- Document ingestion: The process of importing, parsing and indexing documents so they can be searched, analyzed or processed by software.
Reader FAQ
What does the role involve day to day?
Shipping production code across the stack, speaking with users, building ingestion pipelines, creating AI-driven workflows and improving system reliability.
What compensation and equity are offered?
The posting lists a salary between £80k and £120k and equity of about 0.50%–1.00%.
Where is the job located and what is the on-site expectation?
London, with a minimum expectation of three days per week in the office near Bank.
How do I apply and how quickly will I hear back?
Email the founders at the address shown on the listing with examples of your work and a LinkedIn link; the posting says applicants will get a response within 24 hours.
AboutCompaniesStartup JobsFind a Co-FounderLibrarySAFEResources Apply Crimson The AI Associate for Litigation Lawyers Founding Engineer (Full Stack) £80K – £120K GBP • 0.50% – 1.00% • London, England, GB Job type…
Sources
- Crimson (YC X25) is hiring founding engineers in London
- Founding Engineer (Full Stack) at Crimson (YC X25)
- Founding Engineer (Full Stack) job in London
- Founding Full Stack Engineer – w/ Equity
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