"Please, don’t kill the only model that still feels human": Understanding the #Keep4o Backlash

When OpenAI replaced GPT-4o with GPT-5, it triggered the #Keep4o user resistance movement, revealing a conflict between rapid platform iteration and users’ deep socio-emotional attachments to AI systems. This paper presents a phenomenon-driven, mixed-methods investigation of this conflict, analyzing 1,482 social media posts. Thematic analysis reveals that resistance stems from two core investments: instrumental dependency, where the AI is deeply integrated into professional workflows, and relational attachment, where users form strong parasocial bonds with the AI as a unique companion. Quantitative analysis further shows that the coercive deprivation of user choice was a key catalyst, transforming individual grievances into a collective, rights-based protest. This study illuminates an emerging form of socio-technical conflict in the age of generative AI. Our findings suggest that for AI systems designed for companionship and deep integration, the process of change—particularly the preservation of user agency—can be as critical as the technological outcome itself.