This posting is for proactive recruitment purposes and may be used to fill current openings or future vacancies within our organization. Thomson Reuters is building the AI platform that will power the next decade of tax, accounting and audit products, including CoCounsel Audit, a suite of AI‑native products used by accountants on real client work every day. As a Principal Software Engineer, you will own core backend and AI orchestration systems that turn frontier models into reliable, production‑grade workflows at scale. This role is for the CoCounsel for Audit team, formed from the recent acquisition of the startup Materia.About The RoleOwn the AI backbone: principal engineer responsible for the backend and orchestration layer powering AI agents, conversations, workspaces, and knowledge base across CoCounsel for Audit.Shape the company's AI platform and patterns: define patterns for building MCP servers, designing agents, novel uses of LLMs, experimentation, and scalable infrastructure. Your decisions will influence multiple product lines, not just a single feature.Work at real production scale: build and evolve systems that operate over millions of documents, highly structured tax data, ever changing laws, and thousands of concurrent AI interactions from accountants doing time‑sensitive work.Small team, big surface area: join a tight group of senior engineers and researchers shipping quickly, with direct access to product leadership and customers. Think ownership of a startup with the runway of a public company.Great fit for managers who miss building: this role is intentionally designed for senior engineers and engineering managers who want to move back into a high‑impact IC track. You keep the scope and influence of an EM – driving multi‑team initiatives, setting technical direction, mentoring senior engineers – but spend most of your time in the code and architecture of AI systems instead of in 1:1s and status meetings.What You'll DoLead multi‑quarter initiatives that cut across AI, product, and infra (e.g., a new orchestration layer, a low‑latency retrieval system, or a unified knowledge base).Mentor staff and senior engineers, raising the bar on system design, code quality, and AI integration practices across the org.Be the expert in new model capabilities, collaborating closely with AI/ML engineers, researchers, designers, and PMs to translate industry improvements into reliable, user‑facing workflows that accountants trust.Help shape the team’s roadmap, technical strategy, and engineering culture – from experimentation practices to testing, rollout, and postmortems.Help define and lead the platform integration strategy across new and existing Thomson Reuters audit systems to provide world class content and solutions for our customers.Technical Leadership and Cross‑Functional InfluenceLead multi‑quarter initiatives that cut across AI, product, and infra (e.g., a new orchestration layer, a low‑latency retrieval system, or a unified knowledge base).Mentor staff and senior engineers, raising the bar on system design, code quality, and AI integration practices across the org.Be the expert in new model capabilities, collaborating closely with AI/ML engineers, researchers, designers, and PMs to translate industry improvements into reliable, user‑facing workflows that accountants trust.Help shape the team’s roadmap, technical strategy, and engineering culture – from experimentation practices to testing, rollout, and postmortems.Help define and lead the platform integration strategy across new and existing Thomson Reuters audit systems to provide world class content and solutions for our customers.Design and Own AI‑First Backend SystemsArchitect and implement backend services (Python, FastAPI, PostgreSQL, AWS, Vercel) that power generative AI agents, complex workflows (e.g., tax filing, advisory, audit), and document‑centric experiences.Build and evolve AI orchestration: routing, tool calling, MCP servers, multi‑step workflows, safety and guardrails, and robust error handling around third‑party LLMs (OpenAI, Anthropic, and others).Scale, Reliability, and PerformanceDesign for high‑throughput, low‑latency AI workloads: caching, queuing, rate‑limiting, model failover, and cost/performance tradeoffs.Work with large‑scale data: millions of documents, retrieval and search, vector stores, and indexing strategies tailored to tax and accounting use cases.Establish and refine SLOs, observability, and incident response for AI systems that must be correct, auditable, and trustworthy in professional workflows.About You You are a fit for the position of Principal Software Engineer if your background includes:Required Experience & SkillsBachelor’s Degree in Computer Science, Computer Engineering, Related Field, or Equivalent Experience8-10+ years of experience in backend development, building scalable web services and APIs.Deep Python expertise and experience with production systems using frameworks like FastAPI (or similar), relational databases (PostgreSQL or equivalent), and a major cloud provider (AWS preferred).Strong background in distributed systems: data modeling, API contracts, observability, resilience patterns, and performance tuning under load.Proven track record owning large, complex projects end‑to‑end: architecture, execution, rollout, and long‑term operation.Excellent communication skills and the ability to partner with product, design, and ML teams in a fast‑moving environment.Demonstrated interest in AI systems and new engineering paradigms: LLMs, agents, retrieval, or similar – you care about what “AI‑native” software should look like.Preferred Skills & ExperienceHands‑on experience integrating LLM APIs (e.g., OpenAI, Anthropic) into production applications, including prompt/response management, cost controls, and safety considerations.Experience with AI‑adjacent infrastructure: vector databases, embeddings, semantic search, or custom retrieval pipelines.Opinions and experience around automated testing, reliability, and release practices for systems with nondeterministic model behavior.Prior experience in domains where correctness, auditability, and compliance matter (fintech, tax, audit, legal, or similar), or strong interest in applying AI in those contexts.Many of our strongest candidates have bounced between EM and senior IC roles. If you’ve been managing for the last few years and want to get closer to the hard technical problems again – without giving up scope or career progression – this principal IC role is built for that pivot.What’s in it For You?Hybrid Work Model: we’ve adopted a flexible hybrid working environment (2–3 days a week in the office depending on the role) for our office‑based roles while delivering a seamless experience that is digitally and physically connected.Flexibility & Work‑Life Balance: Flex My Way is a set of supportive workplace policies designed to help manage personal and professional responsibilities, whether caring for family, giving back to the community, or finding time to refresh and reset. This builds upon our flexible work arrangements, including work from anywhere for up to 8 weeks per year, empowering employees to achieve a better work‑life balance.Career Development and Growth: By fostering a culture of continuous learning and skill development, we prepare our talent to tackle tomorrow’s challenges and deliver real‑world solutions. Our Grow My Way programming and skills‑first approach ensures you have the tools and knowledge to grow, lead, and thrive in an AI‑enabled future.Industry Competitive Benefits: We offer comprehensive benefit plans to include flexible vacation, two company‑wide Mental Health Days off, access to the Headspace app, retirement savings, tuition reimbursement, employee incentive programs, and resources for mental, physical, and financial wellbeing.Culture: Globally recognized, award‑winning reputation for inclusion and belonging, flexibility, work‑life balance, and more. We live by our values: Obsess over our Customers, Compete to Win, Challenge (Y)our Thinking, Act Fast / Learn Fast, and Stronger Together.Social Impact: Make an impact in your community with our Social Impact Institute. We offer employees two paid volunteer days off annually and opportunities to get involved with pro‑bono consulting projects and Environmental, Social, and Governance (ESG) initiatives.Making a Real‑World Impact: We are one of the few companies globally that helps its customers pursue justice, truth, and transparency. Together, with the professionals and institutions we serve, we help uphold the rule of law, turn the wheels of commerce, catch bad actors, report the facts, and provide trusted, unbiased information to people all over the world.Location: Eligible office location(s) for this role include New York City, San Francisco, Los Angeles, Irvine, CA; McLean, VA; Washington, DC. Base compensation range varies across locations: $183,100‑$340,000 USD (or $158,900‑$295,100 USD for other US locations). This role may also be eligible for an annual bonus based on performance.To ensure we can do that, we seek talented, qualified employees in all our operations around the world regardless of race, color, sex/gender, pregnancy, gender identity and expression, national origin, religion, sexual orientation, disability, age, marital status, citizen status, veteran status, or any other protected classification under applicable law. Thomson Reuters is proud to be an Equal Employment Opportunity Employer providing a drug‑free workplace.If you reside in the United States and require an accommodation in the recruiting process, please contact our Human Resources Department at #J-18808-Ljbffr