Principal Software Engineer - ai

Principal Software Engineer-AI

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 and accounting products, including CoCounsel for Tax and Accounting - a suite of AInative 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, productiongrade workflows at scale. This role is for the CoCounsel for Tax and Accounting team, formed from the recent acquisition of the startup Materia.

Why this role is different:

Own the AI backbone: You will be the principal engineer responsible for the backend and orchestration layer powering AI agents, conversations, workspaces, and knowledge base across CoCounsel for Tax and Accounting. 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 timesensitive 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 highimpact IC track. You keep the scope and influence of an EM - driving multiteam 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.

About the Role

In this role as a Principal Software Engineer-AI you will:

• Technical leadership and crossfunctional influence
• 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, userfacing workflows that accountants trust.
• Help shape the team's roadmap, technical strategy, and engineering culture - from experimentation practices to testing, rollout, and postmortems.
• Design and own AIfirst backend systems
• Architect and implement backend services (Python, FastAPI, PostgreSQL, AWS, Vercel) that power generative AI agents, complex workflows (e.g., tax filing, advisory, audit), and documentcentric experiences.
• Build and evolve AI orchestration: routing, tool calling, MCP servers, multistep workflows, safety and guardrails, and robust error handling around thirdparty LLMs (OpenAI, Anthropic, and others).
• Scale, reliability, and performance
• Design for highthroughput, lowlatency AI workloads: caching, queuing, ratelimiting, model failover, and cost/performance tradeoffs.
• Work with largescale 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,AI if your background includes:

• Bachelors Degree in Computer Science, Computer Engineering, Related Field, or Equivalent Experience
• 8-10+ 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 endtoend: architecture, execution, rollout, and longterm operation.
• Excellent communication skills and the ability to partner with product, design, and ML teams in a fastmoving environment.
• Demonstrated interest in AI systems and new engineering paradigms: LLMs, agents, retrieval, or similar - you care about what "AInative" software should look like.

Preferred Skills & Experience

• Handson experience integrating LLM APIs (e.g., OpenAI, Anthropic) into production applications, including prompt/response management, cost controls, and safety considerations.
• Experience with AIadjacent 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, 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.

Note if you are looking for roles at other levels, we are also hiring Staff and Senior engineers. Search for "Materia AI" within all open roles at Thomson Reuters.

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) 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.