Can synthetic users and AI personas replace talking to real customers?

No, but they have real uses. Synthetic users (AI-generated respondents) are good for desk research, generating hypotheses, rehearsing interview guides, and cheap early exploration, and over half of professional researchers now use them somewhere in their process. They fail exactly where founders need truth most: they give overly agreeable, plausible-sounding feedback and cannot reveal surprising real-world behaviour, so use them to sharpen the questions you then take to real customers, never to answer them.