Deloitte, KPMG, PwC, and EY make up the Big Four professional services firms.Emanuele Cremaschi//Getty Images, Craig T Fruchtman/Getty Images, Joan Cros/NurPhoto,, Joan Cros/NurPhoto via Getty Images. AI took hold in the professional services industry in 2025. From who they hire to what they do, the industry is in a moment of transition. This is what Business Insider learned this year about how the Big Four are embracing AI. The Big Four professional services firms are grappling with AI on two fro ...