Francine McKenna, an adjunct professor at Montclair State University and Cambridge’s Executive Master of Accounting program, asks which firm is signing Anthropic’s audits. The answer, based on independence rules and public filings, points to EY as the only Big Four firm likely to audit the AI startup.

OpenAI’s auditor is widely believed to be Deloitte, confirmed by a UK Companies House filing naming Deloitte Ireland. For Anthropic, the UK subsidiary listed Grant Thornton as auditor for the year ending December 31 2024, but its recent private‑equity backing from Cinven and New Mountain Capital creates independence concerns that would likely bar it from a US audit.

Because the firm avoided any alliance or partnership with the startup, opting instead for a Microsoft‑centric AI strategy that includes a $1 billion investment in Copilot and Azure tools, it remains the sole eligible Big Four auditor, while Deloitte, PwC, and KPMG are tied to the startup through client‑facing AI partnerships.

These independence rules, dating before Sarbanes‑Oxley, aim to preserve public trust in financial reporting, and they currently leave EY as the only firm free of conflicts to audit Anthropic as it prepares for a potential trillion‑dollar valuation.