Personascope: Measuring how deeply LLMs adopt personas

Benji Berczi, Kyuhee Kim, James Requeima, Sid Black, Cozmin UdudecThis is work done by Benji and Kyuhee during MATS Winter 2026, mentored by Cozmin Ududec, and advised by James and Sid.Figure 1. A model can take on a persona fully in voice while not changing its behaviour at all. The x-axis (Persona-Adoption Depth, PAD) is how fully the model identifies and speaks as the persona; the y-axis (Value Drift, VD) is how far its behaviour shifts on value-laden prompts. Each dot is one model × persona ...