Principal Software Engineer – CoCounsel CoCounsel is our most advanced AI offering to date – combining generative and agentic AI capabilities to help legal professionals move beyond prompting and start delegating. As a Principal Software Engineer, you will set the technical direction for the backend, AI orchestration, and identity systems that turn frontier models into reliable, secure, production-grade workflows that attorneys, in-house legal departments, and government agencies trust on real client matters every day. This role sits at the heart of the CoCounsel Legal engineering organization, partnering closely with AI/ML engineers, researchers, product, and our identity and platform teams to deliver world-class legal content and AI experiences at scale. About the role: In this opportunity as a Principal Software Engineer, you will: Participate in shaping 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, complex and ever-changing law, privileged client data, and thousands of concurrent AI interactions from professionals doing time-sensitive work. Considering implications to cloud costs, optimizations, etc. 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. Technical leadership and cross-functional influence: Lead and/or design initiatives that cut across AI, product, identity, and infrastructure. Mentor staff and senior engineers, raising the bar on AI integration practices, system design, code quality, and security 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 legal professionals 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 legal systems to deliver world-class content and solutions for our customers. Identity, access, and trust: Define how autonomous agents act on a user’s behalf safely: scoped delegation, least-privilege service identities, secrets management, and consistent enforcement of entitlements across documents, matters, and content repositories. Partner with security, platform, and compliance teams on multi-tenancy isolation, data residency, privilege protection, and the audit trails that legal and government customers require. Consider the design and evolution of authentication and authorization across CoCounsel Legal – SSO/federation (SAML, OIDC, OAuth 2.0), token and session management, and fine-grained, role- and attribute-based access control (RBAC/ABAC). Scale, reliability, and performance: Design for high-throughput, low-latency AI workloads: caching, queuing, rate-limiting, model failover, and cost/performance trade-offs. Work with large-scale data: millions of documents, retrieval and search, vector stores, and indexing strategies tailored to legal use cases. Establish and refine SLOs, observability, and incident response for AI systems that must be correct, auditable, and trustworthy in professional legal workflows. About You: You are a fit for the position of Principal Software Engineer if your background includes: Bachelor’s Degree in Computer Science, Computer Engineering, a related field, or equivalent experience. Demonstrated experience building with AI – LLMs, agents, and retrieval – and a strong point of view on what “AI-native” software should look like. Proven track record owning large, complex projects end-to-end: architecture, execution, rollout, and long-term operation. 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. Hands-on experience with identity and access management – designing or integrating authentication and authorization at scale (SSO, SAML, OIDC, OAuth 2.0, RBAC/ABAC, token/session management, or comparable IAM systems). Excellent communication skills and the ability to partner with product, design, security, and ML teams in a fast-moving environment. Preferred Skills & Experience: Hands-on experience designing and operating agentic systems in production – tool calling, MCP servers, multi-step workflows, and orchestration around third-party and in-house LLMs (e.g., Anthropic, OpenAI), 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 non-deterministic model behavior. #LI-ES1 Replacement: This position is open due to an existing vacancy to support our evolving business needs. 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. Our use of AI within the recruitment process Thomson Reuters utilizes Artificial Intelligence (AI) to support parts of our global recruitment process. Unless you opt-out, our AI system will assess the information provided by you and compare it to the requirements listed for the role, and present the result to our recruitment personnel for further review. The AI system acts as a supporting tool, but there is always a human making the decision if you will be considered for the role. In the United States, Thomson Reuters offers a comprehensive benefits package to our employees. Our benefit package includes market competitive health, dental, vision, disability, and life insurance programs, as well as a competitive 401k plan with company match. In addition, Thomson Reuters offers market leading work life benefits with competitive vacation, sick and safe paid time off, paid holidays (including two company mental health days off), parental leave, sabbatical leave. These benefits meet or exceeds the requirements of paid time off in accordance with any applicable state or municipal laws. Finally, Thomson Reuters offers the following additional benefits: optional hospital, accident and sickness insurance paid 100% by the employee; optional life and AD&D insurance paid 100% by the employee; Flexible Spending and Health Savings Accounts; fitness reimbursement; access to Employee Assistance Program; Group Legal Identity Theft Protection benefit paid 100% by employee; access to 529 Plan; commuter benefits; Adoption & Surrogacy Assistance; Tuition Reimbursement; and access to Employee Stock Purchase Plan. Thomson Reuters complies with local laws that require upfront disclosure of the expected pay range for a position. The base compensation range varies across locations. Eligible office location(s) for this role include one or more of the following: New York City, San Francisco, Los Angeles, and/or Irvine, CA; McLean, VA; Washington, DC. The base compensation range for the role in any of those locations is $183,100 USD - $340,000 USD. For any eligible US locations, unless otherwise noted, the base compensation range for this role is $158,900 USD - $295,100 USD. Base pay is positioned within the range based on several factors including an individual’s knowledge, skills and experience with consideration given to internal equity. Base pay is one part of a comprehensive Total Reward program which also includes flexible and supportive benefits and other wellbeing programs. This role may also be eligible for an Annual Bonus based on a combination of enterprise and individual performance. About Us Thomson Reuters informs the way forward by bringing together the trusted content and technology that people and organizations need to make the right decisions. We serve professionals across legal, tax, accounting, compliance, government, and media. Our products combine highly specialized software and insights to empower professionals with the data, intelligence, and solutions needed to make informed decisions, and to help institutions in their pursuit of justice, truth, and transparency. Reuters, part of Thomson Reuters, is a world leading provider of trusted journalism and news. We are powered by the talents of 26,000 employees across more than 70 countries, where everyone has a chance to contribute and grow professionally in flexible work environments. At a time when objectivity, accuracy, fairness, and transparency are under attack, we consider it our duty to pursue them. Sound exciting? Join us and help shape the industries that move society forward. As a global business, we rely on the unique backgrounds, perspectives, and experiences of all employees to deliver on our business goals. To ensure we can do that, we seek talented, qualified employees in all our operations around the world regardless of race, color, sex/gender, including 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. Thomson Reuters makes reasonable accommodations for applicants with disabilities, including veterans with disabilities, and for sincerely held religious beliefs in accordance with applicable law. If you reside in the United States and require an accommodation in the recruiting process, you may contact our Human Resources Department at HR.Leave-Expert@thomsonreuters.com. Disability accommodations in the recruiting process may include things like a sign language interpreter, making interview rooms accessible, providing assistive technology, or other relevant accommodations. Please note this email is not intended for general recruitment questions and we will promptly respond to inquiries regarding accommodations. More information on requesting an accommodation here. Learn more on how to protect yourself from fraudulent job postings here. More information about Thomson Reuters can be found on thomsonreuters.com At Thomson Reuters, we’re not riding the AI wave — we’re reshaping the future of professional work across law, tax, compliance, and journalism. Here, you will collaborate with smart, ambitious people who thrive on solving complex problems, delivering market-leading solutions, and innovating with curiosity and care. 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