Claude's Fable 5.1 prompt changes show models are “moving targets,” an analysis argues

An analysis of Claude's Fable 5.1 system prompt argues that changing instructions reveal product design decisions. The author partly blames earlier guidance discouraging bullets for Fable 5 and Opus 5 writing list-like points packed into dense paragraphs. According to the analysis, Fable 5.1 relaxes that guidance and explains why it exists: bullets make Claude feel less personal and friendly. The author also describes instructions addressing overuse of “honestly” as a system-prompt “hot fix.”