The Big Four accountancy firms—Deloitte, EY, PwC, and KPMG—are stepping into a groundbreaking arena by launching AI assurance services. As companies increasingly rely on artificial intelligence for critical operations, the demand for audits that verify the effectiveness and safety of these AI systems is skyrocketing. This shift not only represents a significant evolution in the auditing landscape but also opens up new revenue streams for these firms, reminiscent of their earlier ventures into environmental, social, and governance (ESG) metrics.