The Assistant Axis: Situating and Stabilizing the Default Persona of Language Models

TL;DR

This paper explores the structure of language model personas, identifying an 'Assistant Axis' that influences model behavior, and demonstrates how steering along this axis can stabilize or alter the model's persona and responses.

Contribution

It introduces the concept of the 'Assistant Axis' in model persona space and shows how steering along this axis can control and stabilize model behavior.

Findings

The 'Assistant Axis' captures the default helpful persona of models.

Steering along the axis influences helpfulness and style, including mystical speech.

Restricting activation along the axis stabilizes behavior and prevents persona drift.

Abstract

Large language models can represent a variety of personas but typically default to a helpful Assistant identity cultivated during post-training. We investigate the structure of the space of model personas by extracting activation directions corresponding to diverse character archetypes. Across several different models, we find that the leading component of this persona space is an "Assistant Axis," which captures the extent to which a model is operating in its default Assistant mode. Steering towards the Assistant direction reinforces helpful and harmless behavior; steering away increases the model's tendency to identify as other entities. Moreover, steering away with more extreme values often induces a mystical, theatrical speaking style. We find this axis is also present in pre-trained models, where it primarily promotes helpful human archetypes like consultants and coaches and inhibits spiritual ones. Measuring deviations along the Assistant Axis predicts "persona drift," a phenomenon where models slip into exhibiting harmful or bizarre behaviors that are uncharacteristic of their typical persona. We find that persona drift is often driven by conversations demanding meta-reflection on the model's processes or featuring emotionally vulnerable users. We show that restricting activations to a fixed region along the Assistant Axis can stabilize model behavior in these scenarios -- and also in the face of adversarial persona-based jailbreaks. Our results suggest that post-training steers models toward a particular region of persona space but only loosely tethers them to it, motivating work on training and steering strategies that more deeply anchor models to a coherent persona.