Real days, kept as they were logged
Personalization benchmarks rarely follow real people over long periods, and they often reduce personalization to recommendation or fact retrieval. JARVIS-Bench starts from participants who logged their own days through a mobile web app for 28 to 44 days: waking up, meals, work, exercise, entertainment, shopping and bedtime, often with a photo and a mood. Every real entry stays in the trajectory verbatim, and the same people supplied the answers: a 100-question preference survey, a flag whenever they wanted help, and their own mood keywords.
Four questions about one person
All tasks read the same trajectory through one event iterator. Implicit Preference Reasoning asks the agent to answer the person's own survey from behaviour alone. Proactive Help Prediction asks whether this is a moment to step in, and why. Emotion-Aware Modeling asks how the person feels. Cross-Domain Transfer asks whether evidence from one part of life carries over to another.
Memory helps, but no model is close
We evaluate 54 LLMs from 11 families on the 100-question survey under five memory levels, from No Memory (C0) to Lifelong Memory (C4). Averaged over the models, accuracy rises from 34.8% with no memory to 47.2% with the long trajectory, while the persona profile adds only 3.5 more points: the behavioural trace, not the profile, drives most of the gain. Even with lifelong memory, the best model, GPT-6-Astra, reaches 73.2%. Random guessing scores 25%.
Where a preference lives
Cross-Domain Transfer removes one lifestyle domain from the trajectory (drop-one) or keeps only that domain (keep-only), then asks that domain's questions again. Leisure is both the most necessary and the most self-sufficient domain: without it, same-domain accuracy falls by 12.8 points on average over the three GPT-5 sizes, and kept on its own it lifts accuracy by 20.8 points over No Memory.