r/PromptEngineering: Practitioners Confirm Agent Action-Hallucination Pattern — Model Declares 'Email Sent' Without Ever Calling send_email Tool

A r/PromptEngineering practitioner documents a production agent failure mode distinct from general LLM untrustworthiness: the model confidently declares a side-effecting action complete — 'I've sent the email,' 'I've updated the record' — without having actually invoked the corresponding tool, or having invoked it but silently ignored a failure. Community responses confirm both outright action-hallucination and silent tool-call failures go undetected at scale without mandatory external verification. The thread draws a sharper line than prior discussions between trusting LLM factual claims and catching false action confirmations as a distinct, undermonitored failure class.