Simon Willison’s Weblog


Claude's Character (via) There's so much interesting stuff in this article from Anthropic on how they defined the personality for their Claude 3 model. In addition to the technical details there are some very interesting thoughts on the complex challenge of designing a "personality" for an LLM in the first place.

Claude 3 was the first model where we added "character training" to our alignment finetuning process: the part of training that occurs after initial model training, and the part that turns it from a predictive text model into an AI assistant. The goal of character training is to make Claude begin to have more nuanced, richer traits like curiosity, open-mindedness, and thoughtfulness.

But what other traits should it have? This is a very difficult set of decisions to make! The most obvious approaches are all flawed in different ways:

Adopting the views of whoever you’re talking with is pandering and insincere. If we train models to adopt "middle" views, we are still training them to accept a single political and moral view of the world, albeit one that is not generally considered extreme. Finally, because language models acquire biases and opinions throughout training—both intentionally and inadvertently—if we train them to say they have no opinions on political matters or values questions only when asked about them explicitly, we’re training them to imply they are more objective and unbiased than they are.

The training process itself is particularly fascinating. The approach they used focuses on synthetic data, and effectively results in the model training itself:

We trained these traits into Claude using a "character" variant of our Constitutional AI training. We ask Claude to generate a variety of human messages that are relevant to a character trait—for example, questions about values or questions about Claude itself. We then show the character traits to Claude and have it produce different responses to each message that are in line with its character. Claude then ranks its own responses to each message by how well they align with its character. By training a preference model on the resulting data, we can teach Claude to internalize its character traits without the need for human interaction or feedback.

There's still a lot of human intervention required, but significantly less than more labour-intensive patterns such as Reinforcement Learning from Human Feedback (RLHF):

Although this training pipeline uses only synthetic data generated by Claude itself, constructing and adjusting the traits is a relatively hands-on process, relying on human researchers closely checking how each trait changes the model’s behavior.

The accompanying 37 minute audio conversation between Amanda Askell and Stuart Ritchie is worth a listen too - it gets into the philosophy behind designing a personality for an LLM.