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
.

• Own the AI backbone
  :
  You will be the principal engineer responsible for the backend and orchestration layer powering AI agents, conversations, work spaces, 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 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 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.

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

• Lead multiquarter 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, userfacing workflows that accountants trust.
• Help shape the team's roadmap, technical strategy, and engineering culture - from experimentation practices to testing, rollout, and postmortems.

• Architect and implement backend services (Python, FastAPI, Postgre
  
  SQL, 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 third party LLMs (OpenAI, Anthropic, and others).

• Design for highthroughput, low latency AI workloads: caching, queuing, ratelimiting, 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.

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 (Postgre
  
  SQL 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
  .

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