Principal Engineer CoCounsel Audit

About the role

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.

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 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.

Technical leadership and cross‑functional influence.

• Lead 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 post‑mortems.
• 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.

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 document‑centric 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 high‑throughput, low‑latency AI workloads: caching, queuing, rate‑limiting, model fail‑over, and cost/performance trade‑offs.
• 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 if your background includes:

• Bachelor’s 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…