Toward an AI Personalization Index: A 157-Day Single-User Case Study

AI model benchmark performance has reached a saturation point. According to the Stanford 2025 AI Index Report, the performance gap among the top 10 models has narrowed to 5.4%, and the U.S.–China gap stands at only 1.70%. Yet the EY 2025 Work Reimagined Survey (29 countries, 15,000+ respondents) reveals that while 88% of employees use AI, only 5% engage in advanced utilization. This study proposes that the absence of personalization may be an important explanatory variable for this discrepancy. The author conducted an exploratory single-user manual personalization study over 157 days (~1,000 hours) on the Claude platform (Max plan). As the primary evidence, a same-time comparison on the identical model (Opus 4.6) between an established session (30 memory slots) and a new session (0 memory slots) revealed marked differences in context re-explanation frequency, correction requests, and time to first meaningful output. This study proposes a conceptual organizing framework—Experienced Performance ∝ Model Performance × Personalization Index—and preliminarily defines four candidate variables.